Prenatal Care and Screening

• Immunologic tolerance and placental development: Pregnancy involves profound immunologic shifts to prevent rejection of the semi-allogeneic fetus, mediated by regulatory T cells (Tregs), altered Th1/Th2 balance, and production of immunosuppressive cytokines (IL-10, TGF-β). Deficient tolerance mechanisms lead to preeclampsia, recurrent miscarriage, and intrauterine growth restriction (IUGR), while excessive immunosuppression increases susceptibility to opportunistic infections. Screening for chronic infections (HIV, hepatitis B/C, syphilis) and assessment of immunity (rubella, varicella) identifies women at risk for vertical transmission or severe maternal disease. Vaccination during pregnancy against pertussis and influenza provides passive immunity to neonates before they can receive active immunization.

• Placental insufficiency and fetal development: The placenta develops via trophoblastic invasion of spiral arteries (completed by 18-20 weeks), transforming them into low-resistance vessels that accommodate increasing blood flow to support fetal growth. Inadequate remodeling leads to chronic placental insufficiency manifesting as preeclampsia, IUGR, stillbirth, and placental abruption. Serial ultrasound assessment of fetal biometry (growth), amniotic fluid volume, and umbilical artery Doppler studies identifies fetuses at risk for adverse outcomes. Maternal blood pressure monitoring, assessment of proteinuria, and detection of symptoms (headache, right upper quadrant pain, visual changes) enable early recognition of preeclampsia before maternal seizures or eclampsia occur.

• Metabolic and cardiovascular adaptations: Pregnancy induces insulin resistance (particularly in the third trimester), expanded plasma volume (40-50% increase), increased cardiac output, and decreased systemic vascular resistance. Screening for gestational diabetes mellitus (GDM) via oral glucose tolerance testing at 24-28 weeks detects impaired glucose metabolism that increases risk for macrosomia, birth trauma, neonatal hypoglycemia, and later type 2 diabetes in both mother and offspring. Blood pressure evaluation identifies chronic hypertension, gestational hypertension, and preeclampsia, which collectively affect 10-15% of pregnancies and require intensified monitoring and potential pharmacologic intervention.

• Chromosomal and structural abnormality detection: First-trimester combined screening (11-14 weeks) integrates maternal age, serum markers (PAPP-A, hCG), and nuchal translucency ultrasound to calculate individual risk for aneuploidy (trisomy 21, 18, 13) with detection rates of 85-90% for Down syndrome. Second-trimester quad screen (15-20 weeks) uses four serum markers (AFP, hCG, uE3, inhibin A) achieving similar detection rates. Cell-free fetal DNA (cfDNA) testing detects >99% of trisomy 21 with <0.1% false-positive rate, representing a paradigm shift in screening. Detailed anatomic ultrasound (18-24 weeks) visualizes fetal organs, measures biometric parameters, assesses amniotic fluid, and identifies structural anomalies (congenital heart disease, neural tube defects, renal abnormalities) allowing prenatal diagnosis, counseling, and preparation for specialized delivery or neonatal care.

• Infectious disease screening and prevention: Vertical transmission of infections (HIV, hepatitis B, syphilis, toxoplasmosis, cytomegalovirus) during pregnancy or at delivery causes severe fetal/neonatal disease. Serologic screening identifies affected mothers enabling interventions: antiretroviral therapy reducing HIV transmission from 15-45% to <2%, hepatitis B vaccination of neonates preventing chronic infection, penicillin G treatment of syphilis preventing congenital syphilis, and counseling regarding toxoplasmosis avoidance. Group B Streptococcal (GBS) colonization (occurring in 15-30% of women) causes neonatal sepsis, meningitis, and death; rectovaginal culture at 35-37 weeks identifies carriers requiring intrapartum antibiotic prophylaxis.

Factors requiring increased prenatal surveillance and intervention

• Maternal age extremes: Women ≤19 years and ≥35 years experience increased rates of adverse outcomes. Maternal age ≥35 (advanced maternal age) dramatically increases aneuploidy risk—trisomy 21 risk rises from 1/1,500 at age 20 to 1/350 at age 35 and 1/100 at age 40, representing exponential increase driven by maternal meiotic nondisjunction. Adolescent pregnancies carry elevated risks of preeclampsia, preterm birth, and small-for-gestational-age (SGA) infants. Both extremes benefit from earlier and more intensive fetal screening, growth monitoring, and in some cases, delivery at tertiary centers.

• Medical comorbidities: Chronic hypertension increases risk for preeclampsia, placental abruption, IUGR, and preterm birth; diabetes (pregestational type 1/2) increases congenital anomalies (neural tube defects, cardiac malformations, caudal regression syndrome) and fetal macrosomia; maternal autoimmune conditions (systemic lupus erythematosus, antiphospholipid syndrome) increase early pregnancy loss, IUGR, and stillbirth; cardiac disease, renal disease, and pulmonary hypertension may severely compromise pregnancy tolerance.

• Prior obstetric history: Previous preeclampsia increases recurrence risk to 20-50% (depending on prior severity and gestational age of onset); previous preterm birth raises recurrence risk to 15-30%; previous stillbirth (especially unexplained) increases antepartum fetal surveillance requirements; previous intrauterine growth restriction suggests placental dysfunction warranting serial ultrasound and Doppler studies; multiple prior cesarean deliveries increase risks of placental abnormalities (previa, accreta) and uterine rupture.

• Infections and serology: HIV-positive status requires antiretroviral therapy optimization to achieve undetectable viral load (<50 copies/mL) preventing vertical transmission; hepatitis B surface antigen positivity mandates neonatal vaccination and hepatitis B immunoglobulin; syphilis (RPR+, FTA-ABS+) requires penicillin treatment with close monitoring of titers; cytomegalovirus seropositivity in immunocompromised women raises intrauterine infection risk; toxoplasmosis exposure (especially in endemic regions) requires serologic documentation and counseling; varicella seronegative status in non-immune pregnant women may warrant isolation precautions or postpartum vaccination.

• Genetic and family history factors: Personal or family history of genetic disorders (cystic fibrosis, sickle cell disease, hemophilia, muscular dystrophy) may warrant carrier screening, genetic counseling, and prenatal diagnosis; prior child with chromosomal abnormality or congenital anomaly increases recurrence risk and warrants detailed fetal ultrasound; ancestral background influences carrier frequencies (Ashkenazi Jewish, Mediterranean, African ancestry for specific genetic conditions).

• Substance use and behavioral risks: Cigarette smoking increases IUGR, preterm birth, placental abruption, and sudden infant death syndrome risk; alcohol use (especially heavy) causes fetal alcohol spectrum disorder with microcephaly, intellectual disability, and characteristic facial features; illicit drug use (cocaine, amphetamines, opioids) increases preterm birth, IUGR, placental abruption, and neonatal withdrawal; maternal obesity (BMI ≥30 kg/m²) increases gestational diabetes, preeclampsia, cesarean delivery, and thromboembolic complications.

• Reproductive tract anatomy: Uterine anomalies (septate, bicornuate, unicornuate uterus) increase early pregnancy loss and preterm birth; cervical insufficiency history necessitates consideration of cervical cerclage or progesterone supplementation; prior cervical procedures (cone biopsy, LEEP) may increase preterm birth risk; fibroids (particularly submucosal or intracavitary) may cause miscarriage or preterm birth depending on size and location.

• Vaginal bleeding: First trimester bleeding occurs in 20-25% of pregnancies and may indicate threatened miscarriage, complete or incomplete abortion, ectopic pregnancy, or gestational trophoblastic disease. Second and third trimester bleeding suggests placenta previa (painless bleeding), placental abruption (painful bleeding with contractions), or cervical pathology. Quantifying bleeding volume, associated pain, passage of tissue, and vital sign stability guides urgency of evaluation and potential intervention.

• Abdominal or pelvic pain: First trimester pain raises concern for ectopic pregnancy (unilateral cramping, possible shoulder pain from hemoperitoneum), miscarriage, or appendicitis; severe pain with bleeding suggests abruption. Round ligament pain (unilateral, self-limited) represents normal pregnancy physiology. Right upper quadrant pain in the third trimester suggests preeclampsia with hepatic involvement. Recurrent contractions (after 20 weeks) may represent preterm labor.

• Hypertension and symptoms of preeclampsia: Blood pressure elevation, particularly rapid rise from baseline, triggers further evaluation. Symptoms including severe headache, visual disturbances (scotomata, blurred vision), right upper quadrant or epigastric pain, and rapidly progressive edema suggest preeclampsia. Eclampsia presents with seizures (generalized tonic-clonic) in preeclamptic women, representing a medical emergency. HELLP syndrome (hemolysis, elevated liver enzymes, low platelets) causes right upper quadrant pain, nausea, jaundice, and represents severe preeclampsia.

• Decreased fetal movement: Maternal perception of fetal movement typically begins at 16-20 weeks and increases through pregnancy. Acute decrease in movements (subjectively reported) warrants fetal monitoring via non-stress test (NST) or biophysical profile to exclude fetal distress or demise. Stillbirth risk increases substantially when fetal movement ceases.

• Vaginal discharge changes: Increased clear or slightly turbid discharge represents normal physiologic changes from estrogen stimulation and cervical edema. Purulent, malodorous, or blood-tinged discharge suggests infection (bacterial vaginosis, trichomoniasis, cervicitis) or cervical pathology. Severe itching suggests candidal vulvovaginitis, common in pregnancy due to vaginal glycogen accumulation. Copious discharge with foul odor and pelvic pain suggests intrauterine infection (chorioamnionitis).

• Lower extremity edema and leg pain: Mild bilateral ankle edema is common in the third trimester from reduced venous return and plasma volume expansion. Unilateral leg swelling, pain, warmth, and palpable cord suggest deep vein thrombosis (DVT), with 5-10 times increased risk in pregnancy and the postpartum period due to venous stasis, endothelial injury, and hypercoagulability. Pelvic veins are most commonly affected; presentation may be subtle.

• Shortness of breath and chest pain: Dyspnea is common in pregnancy (from elevated diaphragm, increased minute ventilation), but acute dyspnea with chest pain, tachycardia, and hypoxemia suggests pulmonary embolism (massive pregnancy risk factor), amniotic fluid embolism, or peripartum cardiomyopathy—all requiring urgent evaluation and intervention.

Initial visit (typically <13 weeks 6 days)

• Detailed obstetric and medical history establishes baseline: age, gravity, parity, prior pregnancy outcomes (live births, miscarriages, ectopic, terminations), prior cesarean deliveries with indications and complications, prior preterm births, prior stillbirths, and detailed reasons for each. Medical history includes diabetes, hypertension, cardiac disease, renal disease, thromboembolism, neurologic conditions, and psychiatric history. Medication review identifies teratogens requiring counseling or adjustment. Surgical history documents prior abdominal/pelvic operations. Family history elicits genetic disorders, consanguinity, and advanced paternal age (increasing aneuploidy risk). Exposure history includes cigarettes, alcohol, illicit drugs, and occupational exposures.

• Dating of pregnancy: Accurate gestational age determination is critical for appropriate screening timing, growth assessment, and delivery planning. Last menstrual period (LMP) confirms dating if cycles are regular; accuracy is ±3-4 days. First trimester ultrasound (before 14 weeks) achieves accuracy of ±3-5 days via measurement of crown-rump length (CRL). Second trimester ultrasound (14-20 weeks) via biparietal diameter (BPD) and femur length (FL) is accurate to ±1-2 weeks. Third trimester dating is least accurate (±3-4 weeks) and should not be used to revise dates established in first trimester without compelling reason.

• Vital signs and baseline measurements: Blood pressure (establishes baseline for hypertension assessment), weight (calculates BMI; excessive gain increases gestational diabetes and preeclampsia risk, while inadequate gain increases IUGR risk), and height. Pelvic examination includes cervical inspection (discharge, lesions, cervicitis), Pap smear if not current, and bimanual examination to assess uterine size (should correlate with dates), adnexal masses, and nodularity. Pelvic adequacy assessment (diagonal conjugate, pelvic inlet diameter estimation) may predict cephalopelvic disproportion, though clinical pelvimetry is increasingly replaced by imaging when disproportion is suspected.

• Laboratory screening and serology (first visit):
• Complete blood count (CBC): Hemoglobin <11 g/dL in first/second trimester or <10.5 g/dL in third trimester indicates anemia; iron supplementation is standard in pregnancy. Platelet count baseline (<150,000/μL suggests thrombocytopenia requiring monitoring for preeclampsia-related thrombocytopenia).
• Blood type and antibody screen: ABO/Rh status identifies Rh-negative women (13% of white, 7% of black, 1% of Asian populations) at risk for alloimmunization; indirect Coombs test detects unexpected antibodies. Rh-negative unsensitized women receive RhIG (300 μg IM) at 28 weeks and postpartum if infant is Rh-positive; additional doses given after events causing fetomaternal hemorrhage (bleeding, procedures).
• Infectious disease serology: HIV antibody (fourth-generation antigen/antibody test detects >99% of infections; undetectable viral load with antiretroviral therapy prevents vertical transmission); hepatitis B surface antigen (positive results mandate neonatal vaccination and immunoglobulin); hepatitis C antibody and/or RNA (vertical transmission risk approximately 5-6%, higher with HCV viremia); syphilis serology—RPR or VDRL (nontreponemal test) followed by FTA-ABS or TP-PA (treponemal confirmatory test); varicella antibody (seronegative women counseled on avoidance; postpartum varicella vaccination considered). Rubella serology confirms immunity (titers ≥1:8 protective); seronegative women receive postpartum vaccination. Toxoplasmosis serology considered in endemic areas or with exposure history.
• Complete metabolic panel: Glucose (baseline fasting or random), creatinine (elevated baseline suggests chronic kidney disease), BUN, electrolytes.
• Urinalysis:

Universal first-line measures (ACOG, USPSTF, CDC/ACIP)

• Folic acid supplementation: 400–800 mcg daily preconception through the first trimester (USPSTF); 4 mg daily if a prior child had a neural tube defect. Folate is required for methylation and thymidylate synthesis during neural tube closure, which is complete by ~28 days — supplementation started after a positive pregnancy test is often too late.
• Low-dose aspirin 81 mg daily, begun between 12 and 28 weeks (ideally before 16 weeks) for women at high or multiple moderate risk of preeclampsia (USPSTF and ACOG). Aspirin irreversibly acetylates platelet COX-1, shifting the thromboxane–prostacyclin balance and improving spiral artery perfusion.
• Vaccination (ACIP): inactivated influenza vaccine in any trimester; Tdap in every pregnancy at 27–36 weeks to maximize transplacental IgG against pertussis; COVID-19 vaccine; and maternal RSV prefusion F vaccine seasonally in late pregnancy.
• Iron and prenatal vitamins for physiologic and iron-deficiency anemia.

Screen-triggered therapy

• Syphilis: parenteral penicillin G benzathine is the only accepted regimen; penicillin-allergic patients require desensitization, not a cephalosporin substitution (CDC STI Treatment Guidelines).
• HIV: combination antiretroviral therapy to viral suppression, plus intrapartum zidovudine and cesarean delivery if viral load remains high.
• Asymptomatic bacteriuria: treat with a culture-directed antibiotic to prevent pyelonephritis and preterm birth.
• Rh-negative, unsensitized: anti-D immune globulin 300 mcg at 28 weeks and postpartum, and after any sensitizing event.
• Gestational diabetes (ACOG/ADA): medical nutrition therapy and exercise first; insulin is the preferred pharmacologic agent, with metformin as an alternative.
• Chronic hypertension: beta blocker (labetalol) or dihydropyridine calcium channel blocker (nifedipine XL); methyldopa is second-line.
• Short cervix: vaginal progesterone; cerclage for cervical insufficiency.

Complications of the underlying pregnancy that screening is designed to catch

• Preeclampsia with severe features / eclampsia — emergency. Defective spiral artery remodeling releases antiangiogenic factors (sFlt-1) causing endothelial dysfunction; signaled by new severe-range hypertension with headache, scotomata, or right upper quadrant pain. Seizure means eclampsia and mandates magnesium sulfate and delivery.
• HELLP syndrome — emergency. Microangiopathic hemolysis with schistocytes, rising transaminases, and falling platelets; hepatic capsular hemorrhage can rupture.
• Rh alloimmunization and hydrops fetalis: maternal anti-D IgG crosses the placenta and hemolyzes fetal RBCs; signaled by a rising antibody titer and elevated MCA peak systolic velocity on Doppler.
• Congenital infection: untreated syphilis (hepatosplenomegaly, snuffles, saber shins), untreated HBV (chronic carriage), and GBS colonization (early-onset neonatal sepsis/meningitis).
• Undiagnosed GDM: fetal hyperinsulinemia drives macrosomia, shoulder dystocia, and neonatal hypoglycemia after cord clamping.

Complications of screening and treatment

• Invasive diagnostic testing: amniocentesis and CVS carry a small but real procedure-related pregnancy loss risk; CVS performed before 10 weeks has been linked to limb-reduction defects. Signaled by leaking fluid, cramping, or bleeding after the procedure.
• False-positive serum screening: the quad screen and combined screen have appreciable false-positive rates, prompting unnecessary invasive testing and parental anxiety. Cell-free DNA has a very low false-positive rate but a positive predictive value that falls sharply in low-risk, young patients; confined placental mosaicism, vanishing twin, and rarely maternal malignancy produce discordant results.
• Magnesium sulfate toxicity — emergency: loss of deep tendon reflexes precedes respiratory depression and cardiac arrest; treat with IV calcium gluconate.
• Insulin therapy: maternal hypoglycemia, particularly with postpartum drop in insulin resistance.
• Penicillin for syphilis: Jarisch–Herxheimer reaction with fever, contractions, and transient fetal heart rate abnormalities — monitor, do not withhold treatment.
• Anaphylaxis to intrapartum penicillin — emergency: treat with intramuscular epinephrine 0.3 mg.

• Elevated maternal serum AFP: the single best next step is an ultrasound to confirm dating — incorrect gestational age is the most common cause. Other causes are open neural tube defects, ventral wall defects (omphalocele/gastroschisis), multiple gestation, and fetal demise.
• Quad screen patterns: trisomy 21 = low AFP, low estriol, high hCG, high inhibin A; trisomy 18 = low AFP, low estriol, low hCG with normal inhibin A. Increased nuchal translucency points to aneuploidy but also to Turner syndrome (cystic hygroma) and congenital heart disease even with a normal karyotype.
• cfDNA is a screening test, not a diagnostic test. A positive result must be confirmed with CVS or amniocentesis before any irreversible decision — this is the most heavily tested distractor. Its PPV is low in young, low-risk women despite >99% sensitivity for trisomy 21.
• Low-dose aspirin 81 mg is the intervention examiners want for a woman with prior preeclampsia, chronic hypertension, pregestational diabetes, renal disease, autoimmune disease, or multifetal gestation (USPSTF/ACOG).
• Rh-negative mother: anti-D immune globulin at 28 weeks and postpartum. It prevents sensitization but does not help an already-sensitized woman with a positive antibody screen — that pregnancy is followed with MCA Doppler.
• GBS: rectovaginal culture in the late third trimester (ACOG specifies 36 0/7–37 6/7 weeks) with intrapartum IV penicillin G. Prophylaxis is given without culture if there is GBS bacteriuria this pregnancy or a prior infant with invasive GBS disease.
• Two-step GDM screening at 24–28 weeks (50 g glucose challenge, then 100 g 3-hour OGTT) is the ACOG-preferred approach; screen early if obesity or other risk factors are present.
• Common trap: a hypertensive pregnant patient on an ACE inhibitor must be switched — labetalol or nifedipine, never an ACEI/ARB, and captopril's short half-life does not make it safe in pregnancy.