# Prenatal and Perinatal Preventive Services

## Overview

Prenatal care is one of the most effective preventive health interventions, reducing maternal and neonatal morbidity and mortality. Key components include preconception counseling, risk assessment, screening for genetic and infectious conditions, chronic disease management, and anticipatory guidance. Advances in prenatal screening (cell-free DNA, expanded carrier screening) have transformed genetic risk assessment. Preeclampsia prevention with low-dose aspirin is a major evidence-based intervention. Postpartum period is increasingly recognized as critical for maternal health screening and intervention. Significant disparities exist in prenatal care access and outcomes by race, ethnicity, and socioeconomic status.

## Preconception Counseling

### Key Components

**Folic acid supplementation**: 400-800 mcg daily for all women of childbearing age; 4 mg daily for high-risk women (prior neural tube defect, antiepileptic drugs) **Medication review**: teratogen assessment (isotretinoin, warfarin, valproic acid, ACEi/ARBs, methotrexate, lithium) **Chronic disease optimization**: diabetes (A1c <6.5% before conception), epilepsy, hypertension, thyroid disease. **Substance use screening**: tobacco, alcohol (no safe level in pregnancy), illicit drugs. **Immunization update**: MMR and varicella if non-immune (live vaccines -- administer before conception); Tdap in each pregnancy (27-36 weeks) **Genetic counseling referral**: advanced maternal age, family history of genetic disorders, consanguinity, ethnic-specific carrier screening.

### Carrier Screening

**ACOG recommendation**: offer carrier screening for cystic fibrosis, SMA, and hemoglobinopathies to all pregnant women or those planning pregnancy. **Expanded carrier screening panels**: screen for 100+ autosomal recessive conditions simultaneously; increasingly adopted. **Ethnic-specific screening**: Tay-Sachs (Ashkenazi Jewish), beta-thalassemia (Mediterranean, Southeast Asian), sickle cell (African descent)

## First Trimester Screening and Interventions

### Genetic Screening Options

**Combined first-trimester screening** (11-14 weeks): nuchal translucency ultrasound + serum markers (PAPP-A, free beta-hCG) Detection rate for trisomy 21: ~82-87%; false positive rate ~5%. **Cell-free DNA (cfDNA) / NIPT** (Non-Invasive Prenatal Testing): analyzes fetal DNA fragments in maternal blood. Available from 10 weeks gestation. Detection rate for trisomy 21: ~99%; false positive rate <0.1%. Also screens for trisomy 18, trisomy 13, and sex chromosome aneuploidies. ACOG (2020): offer to all pregnant women regardless of age/risk (changed from high-risk only) Limitations: screening test (not diagnostic); positive results require confirmatory amniocentesis or CVS. Lower PPV in low-risk populations and for rare aneuploidies; not validated for microdeletions in average-risk populations. Confined placental mosaicism can cause false positives.

| Prenatal Screening Test | Timing | Detection Rate (T21) | False Positive Rate | Type |
|---|---|---|---|---|
| Combined first-trimester (NT + serum) | 11-14 weeks | 82-87% | ~5% | Screening |
| Cell-free DNA / NIPT | ≥10 weeks | ~99% | <0.1% | Screening (not diagnostic) |
| Quad screen (second trimester) | 15-22 weeks | ~81% | ~5% | Screening |
| CVS | 10-13 weeks | Definitive | Miscarriage ~0.1-0.3% | Diagnostic |
| Amniocentesis | 15-20 weeks | Definitive | Miscarriage ~0.1-0.3% | Diagnostic |

### Diagnostic Testing

**Chorionic villus sampling (CVS)**: 10-13 weeks; placental tissue; karyotype and genetic analysis. **Amniocentesis**: 15-20 weeks; amniotic fluid; gold standard for definitive diagnosis. Risk of miscarriage: ~0.1-0.3% for both procedures (lower than historical estimates) Chromosomal microarray analysis: detects submicroscopic copy number variants not seen on standard karyotype.

### First Trimester Infections Screening

HIV (universal, opt-out) Hepatitis B surface antigen (universal) Syphilis (universal; repeat in third trimester and at delivery in high-risk) Rubella immunity. Hepatitis C (universal screening now recommended by ACOG and CDC) Chlamydia and gonorrhea (all pregnant women <25 and those at risk)

## Preeclampsia Prevention

### Risk Assessment

High-risk factors (any one = aspirin indicated): prior preeclampsia, chronic hypertension, type 1 or 2 diabetes, renal disease, autoimmune disease, multifetal gestation. Moderate-risk factors (>=2 = aspirin indicated): nulliparity, obesity (BMI >=30), family history of preeclampsia, age >=35, prior adverse pregnancy outcome, IVF, Black race. USPSTF B recommendation: low-dose aspirin (81 mg daily) starting at 12-16 weeks and continuing through delivery for women at high risk.

### Evidence

ASPRE trial: aspirin 150 mg/day from 11-14 weeks reduced preterm preeclampsia by 62%. Meta-analyses: aspirin started before 16 weeks reduces preeclampsia by ~24% overall and preterm preeclampsia by ~50-60%. No significant increase in bleeding complications at 81-150 mg doses. Must be initiated before 16 weeks for maximal placentation benefit.

## Gestational Diabetes Screening

### Two-Step Approach (Most Common in U.S.)

Step 1: 50 g glucose challenge test (GCT) at 24-28 weeks; threshold >=130 or 140 mg/dL (varies by institution) Step 2: 100 g, 3-hour oral glucose tolerance test (OGTT) if GCT positive; GDM diagnosed if >=2 values meet thresholds (Carpenter-Coustan or NDDG criteria)

### One-Step Approach (IADPSG/WHO)

75 g, 2-hour OGTT at 24-28 weeks; GDM if any one value elevated. Diagnoses more women (~18% vs. ~7% with two-step) ACOG currently recommends the two-step approach; WHO and IADPSG favor the one-step. Controversy: whether the one-step approach improves outcomes enough to justify the increased diagnosis burden and cost.

### Early Screening

Consider early screening (first trimester) for women with BMI >=30, prior GDM, PCOS, family history of diabetes, high-risk race/ethnicity. If early testing meets diabetes criteria (FPG >=126, A1c >=6.5%), classify as preexisting (not gestational) diabetes.

## Prenatal Infections and Vaccinations

### Group B Streptococcus (GBS)

Universal vaginal-rectal culture at 36-37 weeks. Intrapartum antibiotic prophylaxis (penicillin G) for GBS-positive women to prevent early-onset neonatal sepsis. Reduced early-onset GBS disease by ~80% since implementation.

### Tdap Vaccination

Recommended during each pregnancy at 27-36 weeks (regardless of prior vaccination) Provides passive antibody transfer to protect newborn from pertussis in first months of life. Safe and effective; no increased adverse pregnancy outcomes.

### Influenza and COVID-19 Vaccination

Inactivated influenza vaccine: recommended for all pregnant women during flu season. COVID-19 vaccination: recommended during pregnancy (mRNA vaccines); reduces risk of severe maternal illness and provides neonatal passive immunity. RSV vaccine (Abrysvo): FDA-approved for pregnant women at 32-36 weeks (seasonal, September-January) to prevent RSV in infants.

## Postpartum Preventive Services

### Postpartum Depression Screening

USPSTF B recommendation: screen all pregnant and postpartum women for depression. Edinburgh Postnatal Depression Scale (EPDS): validated 10-item screening tool; score >=10 suggests possible depression. PHQ-9: also validated for perinatal depression screening. Prevalence: ~10-20% of postpartum women; higher in those with prior depression, socioeconomic disadvantage, traumatic birth. Treatment: psychotherapy (CBT, IPT), SSRIs (sertraline preferred for breastfeeding), brexanolone (IV, severe PPD), zuranolone (oral, FDA-approved 2023 for PPD)

### Postpartum Visit and "Fourth Trimester"

ACOG recommends contact within 3 weeks postpartum with comprehensive visit by 12 weeks. Address: mood, breastfeeding, contraception, chronic disease management, recovery, future pregnancy planning. Interpret the postpartum period as a window for long-term cardiovascular and metabolic risk assessment (GDM, preeclampsia as risk factors)

<image>A flowchart showing the prenatal genetic screening pathway: starting with first-trimester combined screening or cfDNA/NIPT, branching based on results to diagnostic testing (CVS or amniocentesis) or reassurance. Detection rates, false-positive rates, and timing for each option are annotated. A decision node illustrates patient counseling about the difference between screening and diagnostic testing. Prenatal genetic screening education illustration.</image>

<image>A timeline of key prenatal preventive services across trimesters: preconception (folic acid, medication review, carrier screening), first trimester (genetic screening, infection screening, aspirin initiation for preeclampsia prevention), second trimester (anatomy scan, GDM screening at 24-28 weeks, amniocentesis if indicated), third trimester (Tdap vaccination, GBS culture at 36-37 weeks, RSV vaccine), and postpartum (depression screening, contraception, chronic disease follow-up). Each intervention is mapped to its recommended gestational age range. Prenatal care timeline education illustration.</image>

<image>A risk stratification diagram for preeclampsia prevention showing high-risk factors (any one sufficient) and moderate-risk factors (two or more needed) that indicate low-dose aspirin prophylaxis. The evidence base (ASPRE trial: 62% reduction in preterm preeclampsia) and timing (initiate at 12-16 weeks) are annotated. A bar graph overlay compares preeclampsia rates with and without aspirin in high-risk women. Preeclampsia prevention education illustration.</image>

## Clinical Pearls

Cell-free DNA (NIPT) has the highest sensitivity for trisomy 21 (~99%) but remains a screening test -- a positive cfDNA result must be confirmed by amniocentesis or CVS before any irreversible decision. Low-dose aspirin for preeclampsia prevention must be started before 16 weeks gestation to be effective -- the window of benefit is during trophoblast invasion and placentation. GDM and preeclampsia are now recognized as cardiovascular risk factors -- the postpartum period should include counseling about long-term cardiometabolic risk. Universal opt-out HIV screening in pregnancy is standard of care -- identifying HIV-positive mothers and initiating ART reduces vertical transmission to <1%. For boards: know the cfDNA detection rates and limitations (PPV varies by prevalence), aspirin dosing and timing for preeclampsia, the two-step vs. one-step GDM screening debate, and GBS prophylaxis protocol.

## References

- ACOG. Practice Bulletin No. 226: Screening for fetal chromosomal abnormalities. Obstet Gynecol. 2020;136(4):e48-e69.
- Rolnik DL, et al. Aspirin versus placebo in pregnancies at high risk for preterm preeclampsia (ASPRE). N Engl J Med. 2017;377(7):613-622.
- USPSTF. Screening for preeclampsia: preventive medication. JAMA. 2017;317(16):1661-1667.
- USPSTF. Screening for depression and anxiety in perinatal women. JAMA. 2023;329(8):667-678.
- ACOG. Committee Opinion No. 822: Screening for bacterial vaginosis and Group B Streptococcus. Obstet Gynecol. 2021.