# Seminar 01: Normal Pregnancy and Prenatal Care ## Year 3: Obstetrics and Gynecology Clerkship --- ## Learning Objectives By the end of this seminar, students will be able to: 1. Calculate gestational age and estimated date of delivery 2. Describe physiologic changes of pregnancy 3. Apply prenatal visit schedule and components 4. Interpret routine prenatal laboratory tests 5. Counsel patients on nutrition and lifestyle in pregnancy 6. Recognize teratogenic exposures --- ## Seminar Outline ### I. Pregnancy Dating and Terminology The terminology used to describe a woman's reproductive history provides essential clinical information that guides prenatal care. Gravidity refers to the total number of pregnancies a woman has experienced, including the current pregnancy, while parity describes the number of pregnancies that have reached viability, typically defined as 20 weeks or greater gestational age. The TPAL system offers a more detailed breakdown of obstetric history by documenting Term deliveries, Preterm deliveries, Abortions (both spontaneous and induced), and Living children. Understanding this terminology enables clinicians to identify patients at higher risk for complications based on their reproductive history and to counsel appropriately regarding anticipated outcomes. Gestational age calculation forms the foundation of obstetric care and is measured from the first day of the last menstrual period (LMP), while fetal age (also called conceptual age) is approximately two weeks less than gestational age since conception typically occurs around day 14 of a 28-day menstrual cycle. Naegele's rule provides a simple method to calculate the estimated date of delivery (EDD) by adding 7 days to the LMP date, subtracting 3 months, and adding 1 year. This calculation assumes a 28-day menstrual cycle with ovulation occurring on day 14, which represents the average but not universal pattern. When the LMP is uncertain or menstrual cycles are irregular, ultrasound dating becomes essential for establishing accurate gestational age. First trimester ultrasound provides the most accurate dating, with crown-rump length (CRL) measurement being highly precise before 9 weeks, yielding accuracy within 3-5 days. Between 9 and 14 weeks, either CRL or biparietal diameter (BPD) can be used for dating purposes. In the second trimester from 14 to 20 weeks, multiple parameters including BPD, head circumference, abdominal circumference, and femur length are combined to estimate gestational age, though accuracy decreases to plus or minus 7-10 days. Beyond 20 weeks, ultrasound dating becomes progressively less accurate due to normal biological variation in fetal size, and composite measurements should be used with the understanding that the margin of error increases to 2-3 weeks. The pregnancy timeline is divided into three trimesters that correlate with distinct phases of fetal development and maternal adaptation. The first trimester spans from conception through 13 weeks and represents the period of organogenesis when teratogenic exposures carry the highest risk. The second trimester extends from 14 to 27 weeks and is characterized by rapid fetal growth and the development of fetal movement perceptible to the mother. The third trimester from 28 to 40 weeks involves continued maturation of organ systems, particularly the lungs, and significant fetal weight gain. Term pregnancy is defined as 37 to 42 weeks, with post-term pregnancy occurring after 42 completed weeks and carrying increased risks of placental insufficiency and fetal compromise. Panel A: Diagram illustrating Naegele's rule calculation with calendar showing LMP date and EDD calculation. Panel B: Ultrasound images demonstrating crown-rump length measurement in first trimester embryo with calipers placed appropriately. Panel C: Comparison chart showing gestational age dating parameters by trimester with accuracy ranges. Panel D: Timeline graphic depicting the three trimesters with key developmental milestones marked. --- ### II. Physiologic Changes in Pregnancy The cardiovascular system undergoes remarkable adaptations to meet the metabolic demands of pregnancy and the growing fetus. Cardiac output increases by 30-50% above pre-pregnancy levels, achieved through both increased heart rate (10-20 beats per minute higher than baseline) and increased stroke volume. Blood volume expands by 40-50%, beginning in the first trimester and reaching maximum around 32-34 weeks, which serves to protect against hemorrhage at delivery and supply the uteroplacental circulation. Blood pressure typically decreases during the first and second trimesters due to reduced systemic vascular resistance from progesterone-mediated vasodilation, then returns toward pre-pregnancy baseline in the third trimester. These changes explain why pregnant women may experience palpitations, lower extremity edema, and orthostatic symptoms that are normal physiologic responses rather than pathology. Respiratory adaptations ensure adequate oxygen delivery to both mother and fetus while facilitating carbon dioxide elimination. Tidal volume increases significantly while respiratory rate remains essentially unchanged, resulting in increased minute ventilation that creates a state of compensated respiratory alkalosis with PCO2 decreasing from approximately 40 to 30 mmHg. This relative alkalosis facilitates carbon dioxide transfer from the fetal to the maternal circulation across the placenta. Functional residual capacity decreases as the enlarging uterus elevates the diaphragm, which can lead to dyspnea of pregnancy, a common symptom affecting up to 75% of pregnant women. The oxygen consumption of the mother and fetus increases by approximately 20%, necessitating these respiratory adaptations to maintain adequate oxygenation. Hematologic changes in pregnancy create a hypercoagulable state that protects against hemorrhage but increases the risk of venous thromboembolism (VTE). Plasma volume expansion exceeds the increase in red blood cell mass, resulting in the physiologic anemia of pregnancy with hemoglobin levels typically 1-2 g/dL lower than pre-pregnancy values. White blood cell counts increase, with mild leukocytosis up to 15,000/microL being normal, which can make the diagnosis of infection more challenging. Clotting factors VII, VIII, X, and fibrinogen increase substantially, while protein S decreases, creating a 4-5 fold increased risk of VTE during pregnancy and the postpartum period. This hypercoagulable state, combined with venous stasis from uterine compression of the inferior vena cava, underlies the recommendation for VTE prophylaxis in certain high-risk obstetric situations. Renal function adapts to pregnancy through significant increases in glomerular filtration rate (GFR), which rises by approximately 50% above pre-pregnancy levels. This increased filtration results in lower serum creatinine (normal in pregnancy is less than 0.8 mg/dL) and blood urea nitrogen levels than in non-pregnant women. Glucosuria may occur normally in pregnancy due to the increased filtered glucose load exceeding tubular reabsorption capacity. Urinary frequency is common throughout pregnancy due to both increased GFR in early pregnancy and mechanical bladder compression in later pregnancy. Physiologic hydronephrosis, more pronounced on the right side due to dextrorotation of the uterus, occurs from progesterone-mediated smooth muscle relaxation and mechanical compression of the ureters. Panel A: Diagram of cardiovascular changes showing increased cardiac output, blood volume expansion, and decreased systemic vascular resistance with directional arrows. Panel B: Illustration of respiratory physiology changes including elevated diaphragm, increased tidal volume, and decreased PCO2 values. Panel C: Graphic representation of hematologic changes depicting plasma volume expansion exceeding RBC mass increase with coagulation factor alterations. Panel D: Anatomical diagram showing renal adaptations including physiologic hydronephrosis and increased GFR with representative laboratory values. --- ### III. Prenatal Visit Schedule and Components The frequency of prenatal visits follows a standardized schedule that increases as pregnancy progresses to allow for closer monitoring during the higher-risk late third trimester. From the initial visit through 28 weeks, visits typically occur every 4 weeks, providing adequate surveillance while minimizing burden on low-risk patients. Between 28 and 36 weeks, visit frequency increases to every 2 weeks to monitor for complications such as preeclampsia, gestational diabetes complications, and preterm labor. From 36 weeks until delivery, weekly visits allow for assessment of fetal well-being, cervical status, and signs of labor onset. High-risk pregnancies may require more frequent visits, sometimes weekly or twice weekly throughout the third trimester, with the schedule individualized based on the specific risk factors present. The initial prenatal visit is comprehensive and establishes the foundation for all subsequent care. A thorough history encompasses medical conditions, surgical history, detailed obstetric history including prior complications, family history of genetic conditions and pregnancy complications, and social history including substance use and domestic violence screening. The physical examination includes a complete general examination along with pelvic examination to assess uterine size, cervical appearance, and obtain specimens for Pap smear if due. Initial laboratory testing includes complete blood count, blood type and Rh status with antibody screen, rubella immunity, hepatitis B surface antigen, HIV testing, syphilis screening (RPR), and urinalysis with culture to identify asymptomatic bacteriuria. Genetic screening options are discussed and offered based on gestational age and patient preferences. Subsequent prenatal visits follow a structured format that efficiently identifies developing complications while providing ongoing patient education. At each visit, weight is documented to track appropriate gain, blood pressure is measured to screen for hypertensive disorders, and urine is tested for protein as an additional preeclampsia screen. After 20 weeks, fundal height is measured in centimeters, which should correlate with gestational age in weeks (plus or minus 2-3 cm). Fetal heart tones are confirmed at each visit using Doppler auscultation, typically audible by 10-12 weeks with handheld Doppler. Fetal movement (quickening) is typically first perceived by the mother between 16-20 weeks, with primigravidas often noting movement later than multiparous women. Several milestone visits occur at specific gestational ages to perform targeted screening and interventions. Between 11-14 weeks, first trimester screening including nuchal translucency ultrasound may be performed for aneuploidy risk assessment. The quad screen for neural tube defects and aneuploidy is offered between 15-20 weeks if first trimester screening was not done. The anatomy ultrasound at 18-22 weeks evaluates fetal structures for anomalies and confirms placental location. Glucose tolerance testing for gestational diabetes is performed at 24-28 weeks, with earlier screening for women with risk factors. Group B Streptococcus culture is obtained at 35-37 weeks to guide intrapartum antibiotic prophylaxis, and cervical examination begins at 36 weeks or later to assess ripeness and dilation. Panel A: Timeline graphic showing prenatal visit schedule from first trimester through delivery with visit frequency at each stage. Panel B: Checklist illustration of initial prenatal visit components including history, exam, and laboratory testing. Panel C: Diagram of routine assessment at each prenatal visit showing maternal and fetal parameters checked. Panel D: Calendar-style image highlighting milestone visits at specific gestational ages with corresponding tests performed. --- ### IV. Prenatal Laboratory Testing First visit laboratory testing establishes baseline values and identifies conditions requiring intervention or additional monitoring. Complete blood count identifies anemia, which is common in pregnancy and may require iron supplementation, as well as thrombocytopenia that could indicate underlying conditions requiring further evaluation. Blood type and Rh determination is essential for identifying Rh-negative women who will require Rh immune globulin at 28 weeks and after delivery of an Rh-positive infant. Antibody screening detects alloantibodies such as anti-Kell or anti-D that could cause hemolytic disease of the fetus and newborn, necessitating serial monitoring of antibody titers and possibly fetal surveillance. Rubella non-immunity identifies women who should receive MMR vaccination postpartum to protect future pregnancies. Infectious disease screening protects both mother and infant through early identification and treatment. Hepatitis B surface antigen testing identifies chronic carriers whose infants will require hepatitis B immune globulin and vaccination at birth to prevent vertical transmission. HIV screening is offered to all pregnant women, as antiretroviral therapy during pregnancy and delivery can reduce vertical transmission from approximately 25% to less than 1%. Syphilis screening with RPR identifies infected women who require penicillin treatment to prevent congenital syphilis, a devastating condition causing stillbirth, hydrops, and multisystem abnormalities in surviving infants. Urinalysis with culture detects asymptomatic bacteriuria, which occurs in 2-10% of pregnant women and, if untreated, progresses to pyelonephritis in up to 30% of cases, making treatment of asymptomatic infection standard of care. Trimester-specific screening options allow patients to receive information about fetal chromosomal and structural abnormalities. First trimester combined screening includes nuchal translucency measurement by ultrasound along with maternal serum markers (PAPP-A and free beta-hCG), providing approximately 85% detection of trisomy 21 with a 5% false positive rate. Cell-free fetal DNA (cfDNA or NIPT) can be performed from 10 weeks gestation and offers greater than 99% detection of trisomy 21 with lower false positive rates, though it remains a screening test rather than diagnostic. Second trimester quad screening measures alpha-fetoprotein, hCG, estriol, and inhibin A to screen for neural tube defects and trisomies, detecting approximately 80% of trisomy 21 cases. Sequential or integrated screening combines first and second trimester markers for improved detection rates. Glucose screening for gestational diabetes is universally recommended at 24-28 weeks, with earlier screening for women with risk factors such as obesity, prior gestational diabetes, or strong family history. The one-hour glucose challenge test uses a 50-gram glucose load regardless of fasting status, with a threshold of 130-140 mg/dL indicating need for further testing. Women exceeding the threshold undergo a three-hour glucose tolerance test with a 100-gram glucose load after fasting, with diagnosis of gestational diabetes requiring two or more abnormal values (fasting greater than 95, one-hour greater than 180, two-hour greater than 155, three-hour greater than 140 mg/dL). Group B Streptococcus culture obtained at 36-37 weeks by combined vaginal-rectal swab identifies colonized women who will receive intrapartum penicillin prophylaxis to prevent neonatal early-onset GBS sepsis. Panel A: Organized display of first visit laboratory tests showing tubes, requisition forms, and corresponding conditions screened. Panel B: Flowchart of genetic screening options by trimester with detection rates and decision points. Panel C: Diagram illustrating two-step glucose screening process with threshold values and timing. Panel D: Illustration of GBS screening technique showing vaginal-rectal swab collection with positive culture result and intrapartum prophylaxis protocol. --- ### V. Genetic Screening and Diagnostic Testing The distinction between screening and diagnostic testing is fundamental to genetic counseling in pregnancy and patient decision-making. Screening tests identify patients at increased risk for a condition but cannot definitively diagnose or exclude the condition, requiring consideration of sensitivity, specificity, and positive predictive value in interpretation. Diagnostic tests such as chorionic villus sampling (CVS) and amniocentesis provide definitive chromosome analysis through direct examination of fetal cells but carry procedural risks including pregnancy loss. All patients should be offered screening, and those with positive screening results or other indications should be offered diagnostic testing with thorough counseling about the implications of results. The decision to pursue testing is deeply personal and should be guided by the patient's values, beliefs, and desire for information without judgment from the healthcare team. First trimester screening combines ultrasound and biochemical markers to assess risk for chromosomal abnormalities. Nuchal translucency (NT) measurement between 11 and 14 weeks evaluates the fluid collection at the fetal neck, with increased thickness associated with trisomy 21, other aneuploidies, and structural anomalies including cardiac defects. PAPP-A (pregnancy-associated plasma protein A) and free beta-hCG are maternal serum markers that show characteristic patterns in affected pregnancies, with low PAPP-A and elevated beta-hCG seen in trisomy 21. Combined first trimester screening achieves approximately 85% detection of trisomy 21 with a 5% false positive rate. Patients with abnormal first trimester screening or increased NT should be offered diagnostic testing and may benefit from detailed anatomy ultrasound and fetal echocardiography. Cell-free DNA screening (cfDNA, also called non-invasive prenatal testing or NIPT) represents a significant advancement in prenatal genetic assessment. This test analyzes fragments of placental DNA circulating in maternal blood, which can be detected from as early as 10 weeks gestation. Detection rates exceed 99% for trisomy 21 and are also high for trisomies 18 and 13, with very low false positive rates compared to traditional serum screening. However, cfDNA remains a screening test and is not diagnostic; positive results require confirmation with diagnostic testing before any irreversible decisions. The test can also detect sex chromosome abnormalities (Turner syndrome, Klinefelter syndrome) and, in some panels, select microdeletion syndromes, though positive predictive values for these conditions are lower. Diagnostic testing through CVS and amniocentesis provides definitive karyotype analysis and increasingly comprehensive genetic information. CVS is performed between 10-13 weeks by obtaining a sample of placental tissue either transcervically or transabdominally, allowing earlier diagnosis and decision-making. Amniocentesis, typically performed at 15-20 weeks, samples amniotic fluid containing fetal cells shed from skin, respiratory, and urinary tracts. Both procedures carry approximately a 0.5-1% risk of pregnancy loss, though some studies suggest the risk may be lower with experienced operators. Indications for diagnostic testing include positive screening results, advanced maternal age (traditionally 35 years, though screening is now offered to all), prior affected pregnancy, known parental carrier status, or ultrasound findings suggesting anomalies. Panel A: Comparison diagram showing screening versus diagnostic testing with sensitivity, specificity, and risk characteristics. Panel B: Ultrasound image demonstrating nuchal translucency measurement with appropriate caliper placement and normal versus abnormal thresholds. Panel C: Illustration of cfDNA technology showing placental DNA in maternal circulation with analysis methodology. Panel D: Procedural diagrams of CVS (transcervical and transabdominal approaches) and amniocentesis with labeled anatomy. --- ### VI. Nutrition and Weight Gain Recommendations Weight gain recommendations during pregnancy are stratified by pre-pregnancy body mass index (BMI) to optimize maternal and fetal outcomes. Women who are underweight (BMI less than 18.5) are recommended to gain 28-40 pounds to support adequate fetal growth and reduce the risk of preterm birth and low birth weight. Normal weight women (BMI 18.5-24.9) should aim for 25-35 pounds of weight gain, which correlates with optimal birth weight and lowest complication rates. Overweight women (BMI 25-29.9) benefit from more modest gains of 15-25 pounds, while obese women (BMI 30 or greater) should limit gain to 11-20 pounds to reduce risks of gestational diabetes, preeclampsia, cesarean delivery, and macrosomia. Women carrying twins require greater weight gain, with 37-54 pounds recommended for those with normal pre-pregnancy BMI. Nutritional requirements increase during pregnancy to support fetal development and maternal tissue expansion. Caloric intake should increase by approximately 300 kcal per day during the second and third trimesters, with minimal increase needed in the first trimester. Protein requirements increase to 60-70 grams daily to support fetal growth, placental development, and expansion of maternal blood volume and uterine tissue. The diet should emphasize complex carbohydrates, lean proteins, fruits, vegetables, and whole grains while limiting processed foods and added sugars. Women with restricted diets (vegetarian, vegan) may require additional counseling and supplementation to ensure adequate intake of iron, vitamin B12, calcium, and essential amino acids. Prenatal vitamins provide essential micronutrients that are difficult to obtain in adequate amounts through diet alone. Folic acid supplementation of 400-800 mcg daily is critical for preventing neural tube defects and should ideally begin before conception; women with prior affected pregnancies or on certain medications (antiepileptics) require 4 mg daily. Iron supplementation of 27 mg daily prevents iron deficiency anemia, which becomes more likely as pregnancy progresses due to expanded blood volume and fetal iron requirements. Calcium intake of 1000-1300 mg daily supports fetal skeletal development while maintaining maternal bone density. DHA (docosahexaenoic acid), an omega-3 fatty acid, supports fetal brain and retinal development, with 200-300 mg daily recommended either through fish consumption or supplementation. Certain foods should be avoided during pregnancy due to risks of infection or toxic exposure. Raw or undercooked fish, meat, and eggs carry risks of parasitic and bacterial infections including Toxoplasma, Salmonella, and Listeria. Unpasteurized dairy products and soft cheeses, as well as deli meats and hot dogs unless heated to steaming, are associated with Listeria monocytogenes, which can cause miscarriage, stillbirth, and severe neonatal infection. High-mercury fish including shark, swordfish, king mackerel, and tilefish should be avoided due to neurotoxic effects on the developing fetus; low-mercury options like salmon, shrimp, and canned light tuna can be consumed up to 12 ounces weekly. Raw sprouts and unwashed produce may harbor harmful bacteria and should be thoroughly washed or avoided. Panel A: Chart displaying weight gain recommendations stratified by pre-pregnancy BMI with target ranges and trajectory curves. Panel B: Plate illustration showing optimal pregnancy nutrition with appropriate portions of protein, carbohydrates, fruits, vegetables, and dairy. Panel C: Diagram of prenatal vitamin components with corresponding benefits and recommended doses. Panel D: Visual guide of foods to avoid during pregnancy with associated pathogens and health risks. --- ### VII. Common Pregnancy Discomforts First trimester discomforts relate primarily to hormonal changes and the metabolic demands of early pregnancy. Nausea and vomiting (morning sickness) affects up to 80% of pregnant women, typically beginning around 6 weeks and resolving by 12-14 weeks, and is managed with small frequent meals, ginger, vitamin B6, and doxylamine (the combination approved as Diclegis/Bonjesta). Profound fatigue is nearly universal in the first trimester, resulting from elevated progesterone levels and the metabolic demands of placentation and organogenesis, and generally improves in the second trimester. Breast tenderness and enlargement occur early due to hormonal stimulation and proliferation of mammary tissue in preparation for lactation. Urinary frequency results from both increased renal blood flow and GFR as well as the enlarging uterus pressing on the bladder before it rises into the abdomen. Second trimester symptoms often relate to the mechanical effects of the growing uterus and continued hormonal influences. Round ligament pain presents as sharp, jabbing discomfort in the lower lateral abdomen with position changes or sudden movements, caused by stretching of the ligaments supporting the uterus. Back pain affects more than half of pregnant women due to postural changes, weight redistribution, and ligamentous laxity from relaxin hormone, and is managed with proper posture, supportive footwear, exercise, and physical therapy. Heartburn and gastroesophageal reflux result from progesterone-mediated relaxation of the lower esophageal sphincter combined with increased intra-abdominal pressure, responding to small meals, antacids, H2 blockers, or proton pump inhibitors. Constipation occurs from progesterone effects on intestinal motility and iron supplementation, managed with increased fiber, fluids, and stool softeners. Third trimester complaints often intensify as the uterus reaches maximum size and the metabolic demands peak. Lower extremity edema affects up to 75% of women by the third trimester due to venous compression by the uterus and increased capillary permeability; elevation and compression stockings help, though sudden or severe edema warrants evaluation for preeclampsia. Shortness of breath occurs as the diaphragm is elevated up to 4 cm by the enlarging uterus, reducing functional residual capacity; this is managed with positioning and reassurance that oxygenation remains normal. Leg cramps, particularly at night, may relate to calcium, magnesium, or potassium imbalances and respond to stretching, adequate hydration, and sometimes supplementation. Braxton Hicks contractions (practice contractions) increase in frequency and intensity and must be distinguished from true labor by their irregular timing, lack of progressive cervical change, and response to hydration and rest. Warning signs require immediate evaluation to rule out serious complications that can threaten maternal or fetal well-being. Vaginal bleeding may indicate placenta previa, placental abruption, or labor onset and requires urgent assessment with ultrasound and fetal monitoring. Severe headache, especially if accompanied by visual disturbances such as scotomata or blurred vision, may signal preeclampsia and warrants blood pressure measurement and laboratory evaluation. Persistent or severe abdominal pain could represent abruption, preterm labor, or other emergencies requiring evaluation. Decreased fetal movement after the period of quickening should prompt immediate fetal assessment with nonstress testing or biophysical profile. Fluid leaking from the vagina suggests rupture of membranes, which requires evaluation with sterile speculum examination and testing for amniotic fluid. Panel A: Timeline showing common discomforts organized by trimester with self-care management strategies. Panel B: Anatomical illustration depicting round ligament stretching, uterine compression of bladder, and diaphragm elevation. Panel C: Comparison graphic distinguishing Braxton Hicks contractions from true labor contractions. Panel D: Warning signs infographic with red flag symptoms and recommended immediate actions. --- ### VIII. Teratogenic Exposures Understanding teratogenic principles is essential for counseling pregnant women about medication safety and environmental exposures. The critical period for teratogenesis is during organogenesis, weeks 3-8 after conception (5-10 weeks gestational age), when major organ systems are forming and susceptibility to structural malformations is highest. Dose-response relationships exist for many teratogens, with higher exposure levels generally correlating with greater risk and severity of effects. Some agents exhibit threshold effects below which adverse outcomes are unlikely, while others, such as alcohol, have no established safe level. Genetic susceptibility creates individual variation in response to teratogenic exposures, explaining why some exposed pregnancies are affected while others are not. Category X medications are absolutely contraindicated in pregnancy due to clear evidence of fetal harm that outweighs any potential benefit. Isotretinoin (Accutane) causes a characteristic pattern of craniofacial, cardiac, and central nervous system defects, with approximately 25% of exposed fetuses affected; women must use two forms of contraception and have negative pregnancy tests before each prescription. Methotrexate, used for rheumatoid arthritis and cancer, causes limb defects, craniofacial abnormalities, and central nervous system malformations and must be stopped well before conception. Thalidomide, historically responsible for thousands of cases of phocomelia (limb reduction defects), is now used for multiple myeloma under strict prescribing controls. Warfarin causes nasal hypoplasia, stippled epiphyses, and central nervous system abnormalities, particularly with first trimester exposure; low molecular weight heparin provides a safe alternative for anticoagulation. Non-medication teratogenic exposures include substances and infections that cause significant fetal harm. Alcohol is the leading preventable cause of intellectual disability in the United States, causing fetal alcohol spectrum disorder characterized by facial dysmorphism, growth restriction, and neurocognitive deficits; there is no established safe amount of alcohol in pregnancy. Tobacco use causes intrauterine growth restriction, preterm birth, and placental abruption, and increases the risk of sudden infant death syndrome. Cocaine causes placental abruption, growth restriction, and prematurity. Radiation exposure above 10 rad (100 mGy) is concerning for fetal harm, though diagnostic imaging rarely approaches this threshold; a single CT abdomen delivers approximately 2-3 rad. TORCH infections (Toxoplasma, Other [syphilis, varicella], Rubella, Cytomegalovirus, Herpes) cause various patterns of congenital anomalies, growth restriction, and developmental disability. Many commonly used medications are considered safe in pregnancy and should be continued when indicated for maternal health. Acetaminophen is the analgesic of choice for pain and fever, with extensive safety data supporting its use throughout pregnancy. For nausea, doxylamine, vitamin B6, and ondansetron are considered safe, with ondansetron reserved for refractory cases due to possible small increase in cleft palate risk. Antacids, H2 receptor blockers (ranitidine, famotidine), and proton pump inhibitors can be used for gastroesophageal reflux. Second-generation antihistamines such as loratadine and cetirizine are preferred for allergies. Asthma medications including inhaled corticosteroids and beta-agonists should be continued, as poorly controlled asthma poses greater risk to the pregnancy than the medications. When prescribing in pregnancy, clinicians should consult current resources such as LactMed and Reprotox rather than relying on the outdated FDA letter categories. Panel A: Timeline diagram showing critical periods of organogenesis with organ-specific vulnerability windows. Panel B: Collection of images showing characteristic features of fetal alcohol spectrum disorder, warfarin embryopathy, and isotretinoin effects. Panel C: Chart of TORCH infections with associated fetal manifestations and transmission routes. Panel D: Reference table of commonly used medications with safety data in pregnancy organized by indication. --- ### IX. Lifestyle Counseling in Pregnancy Exercise recommendations emphasize maintaining physical activity throughout pregnancy with appropriate modifications for safety. The American College of Obstetricians and Gynecologists recommends at least 150 minutes of moderate-intensity aerobic activity per week for pregnant women without contraindications. Safe activities include walking, swimming, stationary cycling, prenatal yoga, and low-impact aerobics, all of which provide cardiovascular benefits without excessive impact or balance risk. Activities to avoid include contact sports, activities with high fall risk (skiing, horseback riding), scuba diving (risk of fetal decompression sickness), and exercising in the supine position after 20 weeks (potential vena cava compression). Contraindications to exercise include placenta previa, preterm labor risk, severe preeclampsia, and certain cardiac or pulmonary conditions; these patients should be counseled individually about activity restrictions. Work considerations involve balancing the benefits of continued employment with potential occupational hazards and pregnancy-related limitations. Most women can safely continue working throughout pregnancy with appropriate accommodations. Jobs involving prolonged standing, heavy lifting (generally greater than 25-50 pounds repeatedly), or exposure to toxic substances may require modification or reassignment. Radiation exposure in healthcare workers should be monitored to ensure doses remain well below teratogenic thresholds (typically less than 500 mrad cumulative). Women should receive education about their legal rights regarding workplace accommodations and maternity leave. Adequate rest is important, and women experiencing excessive fatigue or pregnancy complications may need reduced hours or modified duties. Travel is generally safe during pregnancy with appropriate precautions and timing considerations. Air travel is considered safe until 36 weeks for domestic travel and often 32-35 weeks for international flights, though airline policies vary and should be verified. During flights, pregnant women should walk frequently (every 1-2 hours), stay well hydrated, and consider compression stockings for longer flights to reduce venous thromboembolism risk. Seat belts should be worn with the lap portion below the belly across the hips and pelvis, not across the abdomen. International travel requires consideration of destination-specific risks including endemic infections (Zika virus in affected areas should be avoided), availability of medical care, and recommended vaccinations. Live vaccines (MMR, varicella, yellow fever) are generally contraindicated in pregnancy, though inactivated vaccines (Tdap, influenza, COVID-19) are safe and recommended. Sexual activity is generally safe throughout pregnancy in the absence of specific contraindications. Intercourse does not harm the fetus, cause infection, or induce labor in normal pregnancies, and couples should be reassured about continued intimacy. Contraindications to intercourse include placenta previa (bleeding risk), preterm labor or shortened cervix (theoretically could trigger contractions), ruptured membranes (infection risk), and unexplained vaginal bleeding. Orgasm causes uterine contractions that are not harmful and do not cause preterm labor in normal pregnancies. Positions may need modification in later pregnancy for comfort. Couples should be counseled that changes in libido are normal during pregnancy due to hormonal fluctuations, body image changes, and fatigue. Panel A: Illustrations of pregnant women engaging in safe exercises (swimming, walking, prenatal yoga) with technique pointers. Panel B: Workplace safety diagram showing proper ergonomics, lifting techniques, and hazard avoidance for pregnant workers. Panel C: Travel safety infographic including seat belt positioning, in-flight DVT prevention, and destination considerations. Panel D: Educational diagram addressing sexual activity safety with contraindications clearly marked. --- ### X. Prenatal Care in Special Populations Advanced maternal age, defined as 35 years or older at delivery, carries specific considerations for prenatal care and counseling. The risk of chromosomal abnormalities, particularly trisomy 21, increases exponentially with maternal age, from approximately 1 in 1,250 at age 25 to 1 in 100 at age 40. Women of advanced maternal age also face higher rates of gestational diabetes, preeclampsia, placenta previa, cesarean delivery, and stillbirth. Cell-free DNA screening or invasive diagnostic testing should be offered to all women but is particularly relevant for those of advanced maternal age given their higher baseline risk. These pregnancies may warrant additional monitoring in the third trimester, with some practitioners recommending antenatal testing or earlier delivery, though management should be individualized. Adolescent pregnancy presents unique medical and psychosocial challenges requiring comprehensive support. Nutritional needs are particularly high as the teenage mother may still be growing herself, requiring careful attention to adequate caloric intake and micronutrient supplementation. Social support assessment is critical, as adolescents may face unstable housing, limited financial resources, and relationship challenges; connections to social services, educational programs, and support groups are essential. Complications including preterm birth, low birth weight, and preeclampsia occur at higher rates in adolescent pregnancies. Confidentiality considerations are important, as minors have rights to consent for prenatal care in most jurisdictions; however, involving supportive family members when possible generally improves outcomes. Obesity in pregnancy is increasingly common and significantly impacts maternal and fetal outcomes. Weight gain recommendations are lower for obese women (11-20 pounds for BMI 30 or greater), though achieving these goals can be challenging and dietary counseling is important. Obese women face substantially increased risks of gestational diabetes, preeclampsia, fetal macrosomia, cesarean delivery, wound complications, and stillbirth. Early glucose screening at the first prenatal visit is recommended due to higher rates of undiagnosed pre-existing diabetes. Low-dose aspirin (81 mg daily starting at 12-16 weeks) is recommended for preeclampsia prevention in women with BMI greater than 30 who have additional risk factors. Antenatal testing may be considered in the third trimester given the increased stillbirth risk, though protocols vary among institutions. Multifetal gestation requires intensified prenatal surveillance due to significantly elevated complication rates. Twin pregnancies should be classified by chorionicity (number of placentas) and amnionicity (number of amniotic sacs) early in pregnancy, as monochorionic twins face unique risks including twin-twin transfusion syndrome. Prenatal visits and ultrasounds are more frequent, with growth assessment every 4 weeks for dichorionic twins and every 2 weeks for monochorionic twins. Nutritional requirements are substantially higher, with recommended weight gains of 37-54 pounds for women with normal pre-pregnancy BMI carrying twins. Risks of preterm birth, preeclampsia, gestational diabetes, and growth restriction are markedly increased. Delivery timing varies by chorionicity and presence of complications, with uncomplicated dichorionic twins typically delivered at 38 weeks and monochorionic twins at 36-37 weeks. Panel A: Graph showing risk of trisomy 21 by maternal age with counseling decision points for screening and diagnostic testing. Panel B: Adolescent pregnancy care model showing multidisciplinary team including obstetric, nutritional, social work, and educational support. Panel C: Obesity risk infographic displaying complication rates compared to normal weight with prevention strategies. Panel D: Twin pregnancy diagram showing dichorionic-diamniotic versus monochorionic placentation with corresponding surveillance protocols. --- ## Summary - Dating: Naegele's rule (LMP + 7 days - 3 months) provides EDD; early ultrasound with CRL is most accurate for gestational age - Physiologic changes: Cardiac output increases 30-50%, blood volume increases 40-50%, physiologic anemia develops, GFR increases 50% - Visit schedule: Every 4 weeks until 28 weeks, every 2 weeks until 36 weeks, then weekly until delivery - First visit labs: CBC, type/screen, rubella, hepatitis B, HIV, syphilis, urinalysis with culture; Pap if due - Genetic screening: cfDNA has greater than 99% detection for trisomy 21 but is screening, not diagnostic - GDM screening: 1-hour glucose challenge at 24-28 weeks; 3-hour GTT if abnormal - GBS culture: 36-37 weeks vaginal-rectal swab; positive results require intrapartum antibiotic prophylaxis - Weight gain: 25-35 pounds for normal BMI; 11-20 pounds for obese women - Folic acid: 400-800 mcg daily (4 mg if high-risk) to prevent neural tube defects - Teratogens: Isotretinoin, methotrexate, warfarin, alcohol (no safe amount), tobacco --- ## Key Terms | Term | Definition | |------|------------| | Gravidity | Total number of pregnancies including current pregnancy | | Parity | Number of pregnancies reaching viability (20 weeks or greater) | | Naegele's rule | Method to calculate EDD: LMP + 7 days - 3 months + 1 year | | Crown-rump length | First trimester ultrasound measurement for gestational age dating | | NIPT | Non-invasive prenatal testing using cell-free fetal DNA in maternal blood | | Gestational diabetes | Glucose intolerance first recognized during pregnancy | | Group B Streptococcus | Vaginal-rectal colonizing bacteria requiring intrapartum prophylaxis | | Neural tube defect | Failure of neural tube closure prevented by folic acid supplementation | --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*