# Seminar 8: Fetal Assessment and Surveillance ## Year 3: Obstetrics and Gynecology Clerkship --- ## Learning Objectives By the end of this seminar, students will be able to: 1. Describe methods of fetal surveillance 2. Interpret the nonstress test 3. Perform and interpret the biophysical profile 4. Evaluate Doppler studies 5. Recognize indications for antenatal testing 6. Apply contraction stress test principles --- ## Seminar Outline ### I. Principles of Fetal Assessment The fundamental goal of antenatal fetal surveillance is to identify fetuses at risk for adverse outcomes, particularly stillbirth and neurologic injury, in time to intervene before irreversible damage occurs. Effective surveillance allows clinicians to optimize the timing of delivery, balancing the risks of prematurity against the risks of continued intrauterine exposure to a hostile environment. When testing is normal, it provides reassurance that the fetus is well-oxygenated and unlikely to suffer intrauterine death or significant injury in the near future. All surveillance methods share a common principle: they have very high negative predictive value (a normal test strongly predicts a healthy fetus) but relatively modest positive predictive value (an abnormal test may occur in a fetus that is actually healthy), which is why abnormal results typically prompt further evaluation rather than immediate delivery. The fetal response to hypoxia progresses through a predictable sequence of physiologic adaptations that forms the basis for understanding antenatal testing. Acute hypoxia initially manifests as fetal heart rate decelerations as chemoreceptors detect reduced oxygen and trigger parasympathetic reflexes to conserve oxygen. Chronic hypoxia leads to behavioral changes including decreased fetal movement and breathing movements as the fetus conserves energy, along with oligohydramnios from reduced renal perfusion and urine output. More severe hypoxia results in loss of fetal heart rate variability as the central nervous system becomes depressed and is unable to modulate heart rate normally. The most severe compromise leads to metabolic acidosis with loss of fetal tone, which is among the last biophysical parameters to become abnormal and indicates profound compromise. The physiologic basis of fetal surveillance rests on the understanding that a well-oxygenated fetus with an intact central nervous system will demonstrate certain predictable behaviors and responses. A reactive fetus showing heart rate accelerations demonstrates intact neurologic function and adequate oxygenation of the brainstem and autonomic nervous system. Non-reactive patterns may reflect fetal sleep cycles, maternal sedation, extreme prematurity, or true hypoxia; distinguishing among these possibilities often requires additional testing or extended monitoring. The false positive rate of antenatal testing is relatively high, meaning that many fetuses with abnormal test results will ultimately be delivered healthy; this reflects the tests' sensitivity for detecting abnormality at the expense of specificity. The false negative rate is quite low, with stillbirth occurring within one week of a normal test result in fewer than 1-2 per 1000 tested pregnancies. The timing of initiating antenatal testing depends on the gestational age at which intervention would be considered and the underlying condition prompting surveillance. For most high-risk conditions, testing begins at 32 weeks gestation, when the likelihood of intact survival after delivery is high and the benefits of identifying fetal compromise outweigh the risks of iatrogenic prematurity. Very high-risk conditions such as severe growth restriction or significant fetal anomalies may warrant earlier testing beginning at 26-28 weeks, particularly at centers with excellent neonatal outcomes at these gestational ages. Post-term pregnancies typically begin surveillance at 41 weeks when the risk of stillbirth begins to increase. Testing frequency is usually weekly for most conditions, increasing to twice weekly for higher-risk situations including post-term pregnancy, severe growth restriction, or diabetes with suboptimal control. Panel A: Goals of antenatal surveillance showing identification of at-risk fetus, delivery timing optimization, and test performance characteristics including negative and positive predictive values. Panel B: Fetal hypoxia response progression from acute decelerations through chronic behavioral changes to severe acidosis with loss of tone. Panel C: Physiologic basis of testing showing relationship between central nervous system oxygenation and reactive heart rate patterns. Panel D: Testing initiation timeline by condition severity showing standard 32-week initiation, earlier testing for high-risk conditions, and frequency recommendations. --- ### II. Nonstress Test The nonstress test (NST) is the most commonly used method of antenatal fetal surveillance, based on the principle that a well-oxygenated fetus with an intact neurologic system will exhibit heart rate accelerations in response to fetal movement. The test is performed using external fetal heart rate monitoring with the patient in a semi-recumbent or lateral position to avoid supine hypotension from vena cava compression. Monitoring typically continues for 20-40 minutes, during which time the fetal heart rate tracing is assessed for baseline rate, variability, accelerations, and decelerations. The name "nonstress test" reflects that no external stress such as uterine contractions is applied to the fetus; the test simply observes the fetal heart rate response to the fetus's own spontaneous movements. A reactive NST at 32 weeks gestation or beyond requires the presence of at least two accelerations of the fetal heart rate within a 20-minute window. Each acceleration must reach a peak of at least 15 beats per minute above the baseline and must last at least 15 seconds from the beginning of the acceleration to the return to baseline. Before 32 weeks gestation, the criteria are modified to account for the physiologic immaturity of the fetal autonomic nervous system; accelerations of 10 beats per minute above baseline lasting at least 10 seconds are considered reactive in the preterm fetus. A reactive NST is reassuring and indicates that the fetus is well-oxygenated at the time of testing, with a very low likelihood of intrauterine death in the subsequent week when the clinical situation is stable. A non-reactive NST is defined as failure to meet reactive criteria after 40 minutes of monitoring. The most common cause of a non-reactive NST is a fetal sleep cycle, as fetuses normally alternate between active and quiet sleep states with cycles lasting 20-40 minutes. Maternal sedating medications including narcotics, benzodiazepines, and magnesium sulfate can suppress fetal heart rate reactivity. Extreme prematurity before 28 weeks may result in physiologically non-reactive patterns due to neurologic immaturity. True fetal hypoxia or acidosis can cause non-reactivity as central nervous system depression prevents the normal accelerative response. When an NST is non-reactive, extending the monitoring period, applying vibroacoustic stimulation to awaken the fetus, or proceeding to biophysical profile or contraction stress test helps distinguish sleep from hypoxia. Additional findings on the NST beyond reactivity provide important clinical information. Variable decelerations, characterized by abrupt onset and offset with variable shape and timing relative to contractions, may indicate umbilical cord compression and warrant evaluation of amniotic fluid volume. Late decelerations, characterized by gradual onset and offset occurring after the peak of contractions, suggest uteroplacental insufficiency and are concerning even when mild and infrequent. Prolonged decelerations lasting more than 2 minutes require immediate evaluation and may indicate cord compression, placental abruption, or other acute events. Absent variability (amplitude range less than 5 beats per minute) is concerning for fetal hypoxia or acidosis when it persists. Sinusoidal pattern, characterized by smooth sine-wave oscillations without short-term variability, is associated with severe fetal anemia and represents an ominous finding requiring urgent evaluation. Panel A: NST methodology showing patient positioning, monitoring equipment placement, and tracing components assessed. Panel B: Reactive NST criteria demonstrating acceleration parameters at term (15x15) and preterm (10x10) with example tracings. Panel C: Non-reactive NST causes including fetal sleep, medications, prematurity, and hypoxia with management algorithm. Panel D: Additional NST findings showing variable decelerations, late decelerations, absent variability, and sinusoidal pattern with clinical significance. --- ### III. Biophysical Profile The biophysical profile (BPP) is a comprehensive assessment combining five parameters of fetal well-being, providing a more thorough evaluation than the NST alone. The five components are the nonstress test, fetal breathing movements, fetal body movements, fetal tone, and amniotic fluid volume. Each parameter is scored as either 2 points (normal/present) or 0 points (abnormal/absent), yielding a total score ranging from 0 to 10. The BPP is based on the concept that multiple fetal behaviors are controlled by different areas of the central nervous system that are differentially sensitive to hypoxia, so assessment of multiple parameters provides a more complete picture of fetal status than any single test. The individual components of the biophysical profile assess both acute and chronic markers of fetal well-being. The NST component is scored as 2 points if reactive according to standard criteria, or 0 points if non-reactive. Fetal breathing movements receive 2 points if at least one episode of sustained breathing lasting 30 seconds or more is observed within the 30-minute observation period. Fetal body movements are scored as 2 points if three or more discrete body or limb movements occur during the observation period. Fetal tone receives 2 points if at least one episode of active extension with return to flexion of a limb or trunk, or opening and closing of a hand, is observed. Amniotic fluid volume is assessed as the maximum vertical pocket (MVP), with 2 points assigned if MVP is 2 cm or greater, and 0 points if MVP is less than 2 cm, indicating oligohydramnios. The interpretation and management of BPP scores follows established guidelines based on extensive outcome data. A score of 8-10 with normal amniotic fluid is considered normal and indicates a very low probability of fetal hypoxia or acidosis; routine follow-up is appropriate. A score of 6 is equivocal, and the BPP should be repeated within 24 hours; if the repeat score is 6 or less, delivery should be considered in a term or near-term fetus. A score of 4 is abnormal and indicates possible fetal asphyxia; delivery should be strongly considered if the fetus is viable and the gestational age is appropriate. A score of 0-2 is highly abnormal and indicates probable fetal asphyxia; delivery is generally indicated if the fetus is viable. Notably, oligohydramnios (MVP less than 2 cm) warrants evaluation and possible intervention regardless of the total score, as it may indicate chronic uteroplacental insufficiency. The modified biophysical profile (mBPP) combines the NST with amniotic fluid assessment, providing a more efficient alternative to the full BPP that maintains excellent predictive value. The mBPP combines an acute marker (NST representing current fetal oxygenation status) with a chronic marker (amniotic fluid index reflecting longer-term placental function and fetal renal perfusion). A normal mBPP requires a reactive NST plus amniotic fluid index of 5 cm or greater (or MVP of 2 cm or greater), which together are considered equivalent to a BPP score of 8/8 or 10/10. The mBPP can be performed more quickly than the full BPP and is often used for routine surveillance, with the full BPP reserved for situations where the mBPP is abnormal or equivocal. The predictive value of the mBPP for adverse outcomes is similar to that of the full BPP when both components are normal. Panel A: Five components of the biophysical profile showing NST, breathing, movement, tone, and amniotic fluid with scoring criteria for each. Panel B: Scoring matrix showing normal (2 points) versus abnormal (0 points) criteria for each BPP component with examples. Panel C: BPP score interpretation chart showing management recommendations for scores 8-10, 6, 4, and 0-2 with consideration of gestational age. Panel D: Modified BPP comparison showing combination of NST and AFI, criteria for normal result, and efficiency compared to full BPP. --- ### IV. Amniotic Fluid Assessment Amniotic fluid volume assessment is an essential component of fetal surveillance that reflects both acute and chronic fetal and placental status. The two primary methods of ultrasound assessment are the amniotic fluid index (AFI) and the maximum vertical pocket (MVP or single deepest pocket). The AFI is calculated by summing the deepest vertical pocket measurements in each of four quadrants of the uterus, with the ultrasound transducer held perpendicular to the floor. The MVP is simply the measurement of the single largest vertical pocket of amniotic fluid, measured with the transducer perpendicular to the floor and free of umbilical cord or fetal parts. Normal AFI ranges from 5 to 24 cm, while normal MVP ranges from 2 to 8 cm; values outside these ranges indicate oligohydramnios or polyhydramnios. Oligohydramnios, defined as AFI less than 5 cm or MVP less than 2 cm, indicates reduced amniotic fluid volume that may reflect underlying fetal or placental pathology. In the second and third trimesters, common causes include uteroplacental insufficiency with reduced fetal renal perfusion and urine output, preterm premature rupture of membranes with ongoing fluid loss, and fetal renal anomalies such as bilateral renal agenesis or obstructive uropathy. Post-term pregnancy is commonly associated with oligohydramnios due to declining placental function. Intrauterine growth restriction is frequently accompanied by oligohydramnios as both conditions reflect uteroplacental insufficiency. Oligohydramnios increases the risk of umbilical cord compression during labor, and severe oligohydramnios in the second trimester can lead to pulmonary hypoplasia and limb contractures from prolonged fetal compression. Polyhydramnios, defined as AFI greater than 24 cm or MVP greater than 8 cm, indicates excessive amniotic fluid volume and warrants evaluation for underlying causes. Maternal diabetes, particularly when poorly controlled, is a common cause, as fetal hyperglycemia leads to osmotic diuresis and increased urine output. Fetal anomalies that impair swallowing, such as esophageal atresia, duodenal atresia, or neurologic conditions affecting swallowing coordination, can cause polyhydramnios. Multiple gestation, particularly monochorionic twins complicated by twin-twin transfusion syndrome, may present with polyhydramnios in the recipient twin. Fetal anemia from any cause can lead to high-output cardiac failure and increased urine production. Idiopathic polyhydramnios without identifiable cause accounts for approximately 50% of cases. Polyhydramnios increases the risk of preterm labor from uterine overdistension, malpresentation from excessive fetal mobility, umbilical cord prolapse, and placental abruption. The clinical implications of amniotic fluid abnormalities extend beyond the immediate diagnosis to influence management decisions. Oligohydramnios identified on antenatal surveillance warrants thorough evaluation including review of the clinical history, assessment for rupture of membranes, detailed fetal anatomic survey if not recently performed, and consideration of underlying causes. Management depends on gestational age, severity, and underlying etiology; severe oligohydramnios at term generally indicates delivery, while earlier gestational ages may warrant close surveillance with consideration of amnioinfusion in some cases. Polyhydramnios similarly requires evaluation for underlying causes including glucose screening, detailed fetal anatomic survey, and consideration of fetal echocardiography. Amnioreduction (therapeutic amniocentesis to remove excess fluid) may be indicated for symptomatic polyhydramnios causing maternal respiratory compromise or preterm contractions, though the benefit is typically temporary as fluid reaccumulates. Panel A: Amniotic fluid assessment techniques showing AFI four-quadrant measurement and MVP single deepest pocket measurement with transducer positioning. Panel B: Oligohydramnios causes and consequences including uteroplacental insufficiency, PPROM, renal anomalies, cord compression risk, and pulmonary hypoplasia. Panel C: Polyhydramnios etiology showing diabetes, fetal anomalies, twin-twin transfusion, and fetal anemia with associated complications. Panel D: Clinical management algorithm for fluid abnormalities showing evaluation steps and intervention considerations based on severity and gestational age. --- ### V. Doppler Velocimetry Doppler velocimetry uses ultrasound to assess blood flow velocity waveforms in fetal and uteroplacental vessels, providing information about vascular resistance and fetal cardiovascular status. The umbilical artery Doppler is the most commonly used and best-validated application, assessing blood flow through the umbilical cord as a reflection of placental vascular resistance. Normal umbilical artery waveforms show continuous forward flow throughout the cardiac cycle, including during diastole, indicating low resistance in the placental vascular bed. The systolic-to-diastolic (S/D) ratio quantifies the relationship between peak systolic and end-diastolic flow velocities; elevated ratios indicate increased placental resistance and are associated with intrauterine growth restriction and adverse perinatal outcomes. Progressive abnormalities of umbilical artery Doppler flow correlate with increasing severity of placental dysfunction and fetal compromise. Elevated S/D ratio above the 95th percentile for gestational age represents the mildest abnormality, indicating increased placental vascular resistance. Absent end-diastolic velocity (AEDV) indicates severe placental vascular resistance such that forward flow ceases during diastole; this finding is associated with significantly increased perinatal morbidity and mortality. Reversed end-diastolic velocity (REDV) is the most severe abnormality, indicating that blood actually flows backward in the umbilical artery during diastole due to extremely high placental resistance; fetal mortality risk is very high, and delivery is typically indicated unless the fetus is extremely premature and stable. The progression from elevated S/D ratio to AEDV to REDV often occurs over days to weeks, allowing for optimization of timing of delivery with corticosteroid administration when possible. Middle cerebral artery (MCA) Doppler provides complementary information to umbilical artery assessment and serves specific clinical purposes. The MCA peak systolic velocity (PSV) is used to screen for fetal anemia in cases of red blood cell alloimmunization, parvovirus infection, or other causes of fetal anemia; elevated PSV above 1.5 multiples of the median for gestational age indicates moderate to severe anemia with sensitivity approaching 100%. The MCA pulsatility index reflects cerebral vascular resistance and is used in assessment of growth-restricted fetuses. Brain-sparing or cerebral redistribution occurs when the fetus preferentially shunts blood to the brain in response to hypoxia, manifested as decreased MCA pulsatility index (indicating cerebral vasodilation) relative to umbilical artery resistance. The cerebroplacental ratio (CPR), calculated as MCA pulsatility index divided by umbilical artery pulsatility index, provides an integrated assessment of fetal adaptation to placental dysfunction. The ductus venosus is a fetal vessel connecting the umbilical vein to the inferior vena cava, and its Doppler waveform provides information about fetal cardiac function. Normal ductus venosus flow shows forward flow throughout the cardiac cycle, including during atrial contraction (the a-wave). Abnormal ductus venosus flow, manifested as absent or reversed flow during atrial contraction, indicates elevated central venous pressure and impaired cardiac function. In the severely growth-restricted fetus, abnormal ductus venosus flow represents an advanced stage of deterioration and is often used to guide delivery timing, particularly at early gestational ages when delaying delivery even briefly may improve neonatal outcomes. Ductus venosus assessment is also used in first-trimester screening for aneuploidy, where reversed a-wave flow is associated with increased risk of chromosomal abnormalities and cardiac defects. Panel A: Umbilical artery Doppler methodology showing waveform acquisition and S/D ratio calculation with normal flow pattern. Panel B: Progressive umbilical artery abnormalities showing elevated S/D ratio, absent end-diastolic velocity, and reversed end-diastolic velocity with clinical significance. Panel C: Middle cerebral artery Doppler applications showing PSV measurement for fetal anemia screening and pulsatility index for cerebral redistribution assessment. Panel D: Ductus venosus Doppler showing normal forward a-wave flow and abnormal reversed a-wave flow with clinical implications for growth restriction and aneuploidy screening. --- ### VI. Contraction Stress Test The contraction stress test (CST), also known as the oxytocin challenge test, assesses the fetal heart rate response to the transient hypoxia induced by uterine contractions. During contractions, blood flow through the intervillous space of the placenta is temporarily reduced, causing a brief decrease in oxygen delivery to the fetus. A healthy fetus with adequate placental reserve tolerates this transient hypoxia without adverse effects on heart rate. A fetus with marginal placental reserve may develop late decelerations in response to the added stress of contractions, indicating inability to maintain oxygenation during the periods of reduced placental perfusion. The CST thus provides a stress test of the fetoplacental unit analogous to cardiac stress testing in adults. The methodology of the CST involves inducing uterine contractions until an adequate contraction pattern is achieved, then monitoring the fetal heart rate response. An adequate test requires at least three contractions within a 10-minute window, each lasting 40-60 seconds. Contractions may be induced through nipple stimulation, which causes endogenous oxytocin release from the posterior pituitary, or through intravenous oxytocin infusion starting at low doses and titrating upward. Nipple stimulation is performed by having the patient massage one nipple through clothing for 2 minutes, repeating as needed until adequate contractions are achieved. Continuous fetal heart rate monitoring is performed throughout the test and for 10 minutes after the final contraction to assess for late decelerations. The interpretation of CST results is based on the presence or absence of late decelerations and the quality of the tracing. A negative CST shows no late decelerations with adequate contractions and represents a reassuring result indicating adequate placental reserve. A positive CST shows late decelerations following more than 50% of contractions and indicates possible uteroplacental insufficiency; delivery should be considered if the fetus is at or near term. Equivocal-suspicious results show intermittent late decelerations or significant variable decelerations, requiring further evaluation or repeat testing. Equivocal-hyperstimulatory results show decelerations occurring with contractions more frequent than every 2 minutes or lasting more than 90 seconds; the test should be repeated without the excessive stimulation. An unsatisfactory test fails to achieve adequate contractions and is non-diagnostic. The CST has largely been replaced by the NST and BPP as the primary methods of antenatal surveillance in contemporary practice due to practical considerations. The CST is more time-consuming, typically requiring 1-2 hours compared to 20-40 minutes for an NST. The need to induce contractions carries theoretical risks including preterm labor and, rarely, uterine hyperstimulation or rupture. Contraindications to the CST include conditions where labor or contractions could be harmful, such as placenta previa, vasa previa, prior classical cesarean delivery or extensive uterine surgery, preterm labor in the current pregnancy, and preterm premature rupture of membranes. However, the CST may provide valuable information in specific clinical scenarios when other testing is equivocal or when the clinical question specifically relates to placental reserve under conditions of uterine stress. Panel A: CST physiologic principle showing uterine contraction effects on intervillous blood flow and fetal heart rate response in normal versus compromised placental reserve. Panel B: CST methodology comparing nipple stimulation and oxytocin induction techniques with monitoring requirements. Panel C: CST interpretation categories showing negative (no late decels), positive (late decels >50%), equivocal-suspicious, equivocal-hyperstimulatory, and unsatisfactory results. Panel D: CST contraindications and contemporary role showing placenta previa, prior uterine surgery, preterm conditions, and comparison to NST/BPP. --- ### VII. Indications for Antenatal Testing Maternal conditions that increase the risk of uteroplacental insufficiency or fetal compromise constitute major indications for antenatal fetal surveillance. Pregestational diabetes mellitus, whether type 1 or type 2, warrants testing beginning at 32 weeks due to the increased risk of stillbirth, particularly with poor glycemic control or vascular complications. Chronic hypertension requires surveillance due to the risks of superimposed preeclampsia and placental insufficiency, with testing typically starting at 32 weeks or earlier if complications develop. Preeclampsia mandates immediate initiation of surveillance at the time of diagnosis regardless of gestational age, as the disease can progress rapidly. Systemic lupus erythematosus and antiphospholipid antibody syndrome carry increased risks of placental dysfunction and fetal demise. Chronic kidney disease, cyanotic heart disease, and severe anemia all compromise oxygen delivery to the fetus and warrant surveillance. Pregnancy-specific complications that compromise fetal well-being also require antenatal testing. Intrauterine growth restriction (IUGR) indicates placental insufficiency and requires surveillance beginning at the time of diagnosis, with frequency and intensity of testing based on severity. Oligohydramnios without obvious cause such as ruptured membranes warrants evaluation and ongoing surveillance due to its association with placental dysfunction. Decreased fetal movement reported by the patient requires immediate evaluation, as it may herald impending stillbirth. Post-term pregnancy beyond 41 weeks is associated with increasing stillbirth risk and declining amniotic fluid, necessitating surveillance. Prior stillbirth places women at increased risk for recurrent stillbirth, and testing typically begins at 32 weeks or earlier based on the circumstances of the prior loss. Complicated multiple gestations, particularly monochorionic twins at risk for twin-twin transfusion syndrome, require specialized surveillance protocols. The frequency of antenatal testing is determined by the underlying indication and the severity of the condition being monitored. Weekly testing is appropriate for most stable high-risk conditions including controlled diabetes, chronic hypertension without complications, and history of stillbirth. Twice-weekly testing is recommended for higher-risk situations including post-term pregnancy, preeclampsia, severe or poorly controlled diabetes, and intrauterine growth restriction. Daily testing may be indicated for the most severely compromised fetuses, such as those with severe IUGR and abnormal Doppler studies, when delivery is being delayed to allow further fetal maturation. The frequency of testing should be increased if the clinical situation deteriorates, maternal symptoms change, or test results become concerning. The decision to deliver based on antenatal test results must integrate the test findings with gestational age, underlying diagnosis, and overall clinical context. A persistently non-reactive NST or low BPP score in a term fetus generally indicates delivery, as the risks of continued pregnancy outweigh the minimal risks of delivery at term. In a very preterm fetus, abnormal testing may prompt intensification of surveillance, hospitalization, corticosteroid administration, and close observation rather than immediate delivery. Absent or reversed end-diastolic flow on umbilical artery Doppler in a severely growth-restricted preterm fetus requires balancing the risks of extreme prematurity against the risk of intrauterine demise. Category III fetal heart rate tracings (absent variability with recurrent late or variable decelerations, or sinusoidal pattern) indicate probable fetal hypoxia or acidosis and require expedited delivery unless rapidly reversible causes can be identified and corrected. Panel A: Maternal condition indications showing diabetes, hypertension, preeclampsia, lupus, and chronic kidney disease with testing initiation timing. Panel B: Pregnancy complication indications showing IUGR, oligohydramnios, decreased fetal movement, post-term, and prior stillbirth. Panel C: Testing frequency recommendations showing weekly for stable conditions, twice weekly for higher-risk situations, and daily for severe compromise. Panel D: Delivery decision framework integrating test results with gestational age and underlying diagnosis showing term versus preterm considerations. --- ### VIII. Fetal Movement Counting Fetal movement counting, also known as kick counts, represents the simplest method of fetal surveillance that engages patients in monitoring their own pregnancies between formal testing appointments. The principle underlying kick counting is that a healthy, well-oxygenated fetus demonstrates regular movement as part of normal behavioral patterns, while a compromised fetus may reduce movement to conserve energy. Decreased fetal movement has been associated with adverse outcomes including stillbirth, and maternal perception of decreased movement is one of the few warning signs that may precede intrauterine demise. Patient education about fetal movement counting is recommended for all pregnant women beginning at 28 weeks gestation, with clear instructions about when and how to perform counts and when to seek medical evaluation. The most widely used method of fetal movement counting instructs patients to count fetal movements during a time of typical fetal activity, usually in the evening after dinner when fetuses tend to be most active. The patient is instructed to focus attention on fetal movements while in a comfortable position, typically lying on her side or in a reclined position. The goal is to perceive 10 distinct fetal movements within a 2-hour period; most women will achieve this count in much less time, often within 30-60 minutes. If 10 movements are not perceived within 2 hours, the patient should contact her healthcare provider for further evaluation. Some providers use alternative methods such as counting for a specified time period and recording the number of movements, though the count-to-10 method is most commonly recommended. When a patient reports decreased fetal movement, formal evaluation with NST or BPP should be performed to assess fetal status. In most cases, testing will be reassuring, and the perceived decrease in movement represents normal fetal sleep cycles, changes in maternal attention to fetal activity, or anterior placental position muffling the perception of movement. However, in some cases, evaluation will reveal concerning findings such as oligohydramnios, non-reactive NST, or abnormal BPP, prompting further evaluation or intervention. The threshold for evaluation should be low, as the consequences of missing a fetus in distress are severe and the testing to evaluate decreased movement is non-invasive and readily available. Despite its intuitive appeal and widespread recommendation, the evidence supporting formal fetal movement counting programs as a strategy to prevent stillbirth is limited. Large randomized trials have not consistently demonstrated that formal kick counting protocols reduce stillbirth rates compared to usual care. Concerns have been raised that formal counting may increase maternal anxiety and lead to unnecessary interventions without proven benefit. However, instruction about fetal movement awareness and a low threshold for evaluation of decreased movement remains standard practice, as it may prompt evaluation that detects fetal compromise in some cases. The key is to counsel patients appropriately about the normal variability of fetal movement, the meaning of counting instructions, and when to seek evaluation, to maximize potential benefits while minimizing unnecessary anxiety. Panel A: Fetal movement counting rationale showing relationship between fetal well-being, activity levels, and hypoxia-related movement reduction. Panel B: Count-to-10 methodology showing timing recommendations, patient positioning, counting technique, and action threshold of 10 movements in 2 hours. Panel C: Decreased fetal movement evaluation flowchart showing initial assessment, NST/BPP testing, and management based on results. Panel D: Evidence and limitations discussion showing trial results, anxiety considerations, and appropriate counseling approach. --- ### IX. Ultrasound in Fetal Assessment Routine obstetric ultrasound examinations serve specific purposes at different gestational ages and form the foundation of prenatal diagnosis and fetal assessment. First-trimester ultrasound confirms intrauterine pregnancy location, establishes gestational age through crown-rump length measurement, determines number of fetuses and chorionicity in multiple gestations, and may include assessment of nuchal translucency for aneuploidy screening. The dating scan is most accurate in the first trimester, when embryonic size shows the least variation among normally growing pregnancies. Accurate dating is essential for interpretation of subsequent growth assessments, appropriate timing of antenatal testing, and management of conditions where gestational age influences decision-making such as preterm labor or postdates pregnancy. The detailed anatomy ultrasound, typically performed between 18 and 22 weeks gestation, provides comprehensive evaluation of fetal structures to identify anomalies that may require specialized prenatal care, affect delivery planning, or influence management decisions. The fetal brain is evaluated for ventricular size, midline structures including the corpus callosum, and the cerebellum for size and configuration. The face is assessed for normal lip and palate development. The fetal heart receives detailed attention with assessment of the four-chamber view, outflow tracts, and great vessel relationships; abnormal findings prompt referral for fetal echocardiography. The spine is evaluated for continuity and absence of defects. Abdominal structures including the stomach, kidneys, bladder, and abdominal wall insertion of the umbilical cord are assessed. The extremities are evaluated for presence and normal development of long bones. Third-trimester ultrasound for growth assessment utilizes multiple biometric measurements to estimate fetal weight and evaluate growth trajectory. The biparietal diameter (BPD) measures the fetal head at the level of the thalami and cavum septi pellucidi, representing head width. The head circumference (HC) measures the outer perimeter of the fetal skull at the same level. The abdominal circumference (AC) is measured at the level of the umbilical vein and stomach, representing the most variable measurement that is most sensitive to nutritional status. The femur length (FL) measures the ossified portion of the femoral shaft. These measurements are entered into standardized equations to calculate estimated fetal weight (EFW), which is then plotted against gestational age-specific curves to determine percentile. Growth assessment interpretation requires understanding of normal variation and recognition of patterns suggesting pathology. Appropriate for gestational age (AGA) indicates estimated fetal weight between the 10th and 90th percentiles, representing normal growth. Small for gestational age (SGA) indicates estimated fetal weight below the 10th percentile and requires evaluation to distinguish constitutionally small but healthy fetuses from those with pathologic growth restriction. Large for gestational age (LGA) indicates estimated fetal weight above the 90th percentile and is associated with increased birth trauma risk, particularly in diabetic pregnancies. Serial growth assessments are more informative than single measurements, as the trajectory of growth over time distinguishes normal variation from concerning patterns. A fetus crossing percentile lines (either falling or rising) warrants evaluation even if the absolute measurements remain within normal range. Panel A: First-trimester ultrasound purposes showing location confirmation, crown-rump length dating, multiple gestation assessment, and nuchal translucency screening. Panel B: Anatomy survey components showing systematic evaluation of brain, face, heart, spine, abdomen, and extremities with key structures assessed. Panel C: Growth biometry measurements showing BPD, HC, AC, and FL with landmarks and EFW calculation. Panel D: Growth percentile interpretation showing AGA, SGA, and LGA classifications with serial assessment importance and trajectory concerns. --- ### X. Special Testing Situations Multiple gestation pregnancies require tailored surveillance protocols based on chorionicity, which determines the risks and monitoring needs. Dichorionic twins (either di-di or same-sex dichorionic twins) require growth assessment every 4 weeks to monitor for discordant growth, as each fetus has its own placenta and the risk of twin-twin transfusion syndrome does not apply. Monochorionic twins share a single placenta with vascular connections and require more intensive surveillance with growth assessment every 2 weeks and careful evaluation for signs of twin-twin transfusion syndrome including discordant amniotic fluid volumes, discordant fetal sizes, and abnormal Doppler studies. Antenatal testing with NST or BPP is indicated when complications arise or growth abnormalities are detected, and earlier delivery is typically planned for monochorionic twins due to the ongoing risks of the shared placentation. Post-term pregnancy, defined as pregnancy extending to or beyond 42 weeks (42 weeks 0 days) gestation, carries increased risks that mandate surveillance and consideration of delivery. The stillbirth rate increases approximately 2-fold after 42 weeks compared to delivery at 39-40 weeks, and the rate continues to rise with advancing gestational age. Placental function declines in post-term pregnancy, manifested as decreasing amniotic fluid volume and increasing risk of meconium-stained fluid. Fetal surveillance should begin at 41 weeks with twice-weekly NST or modified BPP, with close attention to amniotic fluid volume. Delivery is recommended by 42 weeks gestation at the latest, and induction of labor between 41 and 42 weeks is associated with improved outcomes compared to expectant management with continued surveillance. Decreased fetal movement reported by the patient requires prompt evaluation regardless of the results of any recent formal testing. Maternal perception of decreased movement may precede detectable abnormalities on testing and has been associated with adverse outcomes in numerous studies. Evaluation typically begins with NST, with progression to BPP if the NST is non-reactive or if clinical suspicion remains high despite reactive NST. Detailed ultrasound examination should assess amniotic fluid volume and may include growth assessment if not recently performed. If all testing is reassuring, the patient can be discharged with instructions to return immediately if movement continues to be decreased. If testing is abnormal, management is guided by the specific findings and gestational age. Prior stillbirth places women at increased risk for recurrent stillbirth in subsequent pregnancies, warranting heightened surveillance and often earlier delivery. The recurrence risk depends on the cause of the prior stillbirth; unexplained stillbirths and those related to placental insufficiency carry higher recurrence risk than stillbirths due to cord accidents or fetal anomalies that are not present in the current pregnancy. Testing typically begins at the gestational age of the prior stillbirth or at 32 weeks, whichever is earlier. Weekly or twice-weekly testing is performed depending on the circumstances. Delivery timing is individualized but is often planned by 39 weeks even if the pregnancy is uncomplicated, given the psychological burden of continuing pregnancy and the difficulty of predicting recurrence. Thorough counseling and psychological support are essential components of care for these families. Panel A: Multiple gestation surveillance comparing dichorionic twin monitoring (growth every 4 weeks) to monochorionic twin monitoring (growth every 2 weeks, TTTS surveillance, Doppler studies). Panel B: Post-term pregnancy management showing stillbirth risk increase, surveillance protocol starting at 41 weeks, and delivery recommendations by 42 weeks. Panel C: Decreased fetal movement evaluation algorithm showing immediate NST, progression to BPP, detailed ultrasound, and management based on findings. Panel D: Prior stillbirth management showing recurrence risk factors, early testing initiation, and delivery timing considerations with psychological support needs. --- ## Summary - NST reactive criteria at 32 weeks or greater: at least 2 accelerations of 15 bpm above baseline lasting at least 15 seconds within 20 minutes - NST non-reactive: criteria not met after 40 minutes; extend monitoring, apply vibroacoustic stimulation, or proceed to BPP - BPP has 5 components scored 0 or 2 points each: NST, fetal breathing, fetal movement, fetal tone, and amniotic fluid (MVP 2 cm or greater) - BPP scores 8-10 are normal; score of 6 requires repeat in 24 hours; scores of 4 or less are abnormal and typically warrant delivery if viable - Modified BPP combines NST plus AFI; reactive NST plus AFI 5 cm or greater is normal - Normal AFI is 5-24 cm; oligohydramnios is AFI less than 5 cm or MVP less than 2 cm; polyhydramnios is AFI greater than 24 cm or MVP greater than 8 cm - Umbilical artery Doppler is used for IUGR evaluation; absent or reversed end-diastolic velocity indicates severe placental dysfunction - MCA Doppler PSV greater than 1.5 MoM indicates fetal anemia; used for Rh alloimmunization and other causes of fetal anemia - Antenatal testing typically begins at 32 weeks for high-risk conditions, with weekly or twice-weekly frequency depending on severity - Fetal movement counting: 10 movements in 2 hours is normal; decreased movement warrants immediate evaluation with NST or BPP --- ## Key Terms | Term | Definition | |------|------------| | Nonstress test | Fetal heart rate monitoring assessing accelerations in response to fetal movement | | Reactive | NST showing appropriate accelerations meeting gestational age-specific criteria | | Biophysical profile | Five-component fetal assessment including NST, breathing, movement, tone, and amniotic fluid | | Amniotic fluid index | Sum of deepest vertical pockets in four quadrants of the uterus | | Oligohydramnios | Decreased amniotic fluid with AFI less than 5 cm or MVP less than 2 cm | | Doppler velocimetry | Ultrasound assessment of blood flow velocity patterns in fetal and uteroplacental vessels | | AREDV | Absent or reversed end-diastolic velocity in the umbilical artery indicating severe placental dysfunction | | MCA PSV | Middle cerebral artery peak systolic velocity used to screen for fetal anemia | --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*