10.1 Routine Antenatal Care, Screening & Fetal Assessment

Routine Antenatal Care & The Caribbean Healthcare Framework

Routine antenatal care (ANC) serves as the primary clinical vehicle for risk stratification, early detection of maternal-fetal pathology, nutritional optimization, and birth preparedness. While the World Health Organization (WHO) 2016 model recommends a minimum of eight antenatal contacts—scheduled at booking (< 12 weeks), 20, 26, 30, 34, 36, 38, and 40 weeks—many regional primary healthcare networks across the English-speaking Caribbean combine this framework with the traditional visit schedule (every 4 weeks until 28 weeks, every 2 weeks until 36 weeks, and weekly thereafter until delivery).

The initial booking visit establishes baseline clinical parameters, validates gestational age, and stratifies obstetric risk:

• Accurate Gestational Dating: Accurate determination of the expected date of delivery (EDD) is essential. While Naegele's rule calculates the EDD by adding 7 days and 9 months (or 1 year minus 3 months) to the first day of the last normal menstrual period (LNMP), early first-trimester ultrasonography measuring crown-rump length (CRL, accurate to within +/- 5 to 7 days between 7 and 13+6 weeks) represents the definitive diagnostic gold standard.
• Baseline Maternal Hemodynamics & Anthropometry: Baseline blood pressure measurement before 20 weeks is critical to differentiate preexisting chronic hypertension from pregnancy-induced hypertensive disorders. Body mass index (BMI) calculation guides gestational weight gain targets and identifies patients requiring early metabolic surveillance.
• Social, Medical, and Obstetric History: Systematic documentation of previous cesarean sections, uterine surgery, recurrent miscarriages, prior preterm birth, history of postpartum hemorrhage, and chronic maternal conditions (cardiac disease, renal impairment, epilepsy, hemoglobinopathies).

First-Trimester Booking Investigations & Hemoglobinopathy Screening

A standardized laboratory panel must be performed at the initial antenatal visit to screen for asymptomatic infections, hematological disorders, and maternal alloimmunization risks:

ABO and Rhesus (RhD) Typing & Antibody Screen

Maternal blood grouping and indirect Coombs testing (red cell antibody screen) must be performed at booking. In non-sensitized RhD-negative women carrying an RhD-positive fetus, transplacental fetomaternal hemorrhage can trigger maternal anti-D IgG alloantibody production. These IgG antibodies cross the placenta in subsequent pregnancies, causing fetal hemolytic disease of the fetus and newborn (HDFN), severe fetal anemia, erythroblastosis fetalis, and hydrops fetalis.

• Prophylaxis: Routine antenatal anti-D immunoglobulin prophylaxis (RAADP) is administered at 28 weeks of gestation as a single dose of 1,500 IU (300 mcg) or split into two doses (at 28 and 34 weeks). A further 1,500 IU dose is given within 72 hours of delivery if the infant is confirmed to be RhD-positive.
• Sensitizing Events: Assess bleeding, pregnancy loss, ectopic pregnancy, invasive testing, abdominal trauma and external cephalic version promptly. Give anti-D within 72 hours when indicated, using the gestation- and event-specific local protocol, particularly in early pregnancy. At or beyond 20 weeks, quantify fetomaternal hemorrhage with a Kleihauer-Betke test or flow cytometry to guide additional doses; do not delay the initial dose for the result.
• Sensitized Patients: If maternal anti-D titers are elevated (>= 1:16 or >= 1:32), anti-D immunoglobulin is ineffective. Management requires serial maternal antibody titration and middle cerebral artery (MCA) Doppler peak systolic velocity (PSV) surveillance; MCA-PSV > 1.5 multiples of the median (MoM) suggests significant fetal anemia and prompts fetal-medicine assessment, usually fetal blood sampling with preparation for intrauterine transfusion if anemia is confirmed and delivery is not safer.

Complete Blood Count & Hemoglobinopathy Evaluation

Physiological plasma volume expansion (40% to 50%) exceeds the increase in red cell mass (20% to 30%), resulting in physiological "hemodilution anemia." The WHO defines anemia in pregnancy as:

• First Trimester: Hemoglobin < 11.0 g/dL (Hematocrit < 33%)
• Second Trimester: Hemoglobin < 10.5 g/dL (Hematocrit < 32%)
• Third Trimester: Hemoglobin < 11.0 g/dL (Hematocrit < 33%)

Nutritional iron deficiency anemia is characterized by microcytic, hypochromic red cells with serum ferritin < 30 mcg/L. However, across the Caribbean population, high frequencies of sickle cell disease (HbSS, HbSC, HbS-beta-thalassemia) and alpha/beta-thalassemia traits mandate routine hemoglobin electrophoresis (or HPLC) at the booking visit. Women with sickle cell trait (HbAS) require continuous monitoring for asymptomatic bacteriuria and urinary tract infections. Mothers with homozygous sickle cell disease (HbSS) face extreme risks of acute chest syndrome, vaso-occlusive bone crises, placental infarction, severe fetal growth restriction, and pre-eclampsia, requiring coordinated maternal-fetal subspecialist care, supplemental folic acid (5 mg daily), and avoidance of dehydration and cold exposure.

Infectious Disease & Asymptomatic Bacteriuria Screening

• Syphilis Serology: Universal screening with non-treponemal tests (VDRL or RPR) confirmed by treponemal testing (TPHA or FTA-ABS). Untreated maternal syphilis leads to congenital syphilis, spontaneous abortion, non-immune hydrops, stillbirth, and neonatal skeletal/neurological defects. Intramuscular Benzathine Penicillin G (2.4 million units IM single dose for primary/secondary/early latent; weekly for 3 consecutive weeks for late latent or unknown duration) is the only proven therapy that prevents vertical transmission; penicillin-allergic gravidas must undergo hospital desensitization.
• HIV Universal Opt-Out Screening: Early identification enables combination antiretroviral therapy (cART) that suppresses maternal plasma viral load to undetectable levels (< 50 copies/mL), reducing vertical transmission rates from > 25% to < 0.5%. Cesarean section is indicated if viral load exceeds 1,000 copies/mL at 36 weeks.
• Hepatitis B Surface Antigen (HBsAg): Identifies chronic maternal carrier status. Neonates born to HBsAg-positive mothers must receive both the Hepatitis B vaccine and Hepatitis B immune globulin (HBIG 0.5 mL IM) at separate anatomical sites within 12 hours of birth, followed by completion of the vaccine series, achieving > 95% protection against perinatal transmission.
• Rubella IgG Immunity: Live-attenuated MMR vaccine is strictly contraindicated during pregnancy due to theoretical teratogenicity. Non-immune women (rubella IgG negative) must avoid contact with rash illnesses and receive postpartum MMR vaccination prior to discharge, with advice to avoid pregnancy for at least 4 weeks.
• Asymptomatic Bacteriuria (ASB): High levels of progesterone cause smooth muscle relaxation, ureteral dilatation, and urinary stasis. A midstream clean-catch urine culture is mandatory at booking (diagnostic threshold: >= 10^5 CFU/mL of a single uropathogen, most commonly Escherichia coli). Untreated ASB progresses to acute maternal pyelonephritis in up to 30% to 40% of cases, triggering preterm labor, sepsis, and low birth weight. Treatment requires a 3 to 7-day course of pregnancy-safe oral antimicrobials (nitrofurantoin [avoid in G6PD deficiency and at term], amoxicillin-clavulanate, or cephalexin), followed by a repeat test-of-cure culture.

Gestational Diabetes Mellitus: Screening, Diagnosis & Glycemic Control

Gestational diabetes mellitus (GDM) is hyperglycemia first detected during pregnancy that is below the diagnostic range for overt diabetes in pregnancy. Human placental lactogen (hPL), progesterone, cortisol, and placental growth hormone exert potent anti-insulinogenic effects that peak during the late second trimester (24 to 28 weeks).

Universal Screening & Diagnostic Criteria

Universal screening is conducted between 24 and 28 weeks of gestation using the 75 g 2-hour Oral Glucose Tolerance Test (OGTT) after an 8 to 14-hour overnight fast. High-risk women (pre-pregnancy BMI >= 30 kg/m², prior macrosomic neonate >= 4.0 kg, history of GDM, polycystic ovary syndrome, or strong first-degree family history of type 2 diabetes) undergo early 75 g OGTT testing at booking; if negative, testing is repeated at 24 to 28 weeks.

Under the internationally validated International Association of Diabetes and Pregnancy Study Groups (IADPSG) and WHO criteria, GDM is diagnosed if one or more plasma glucose values meet or exceed the following thresholds on the 75 g OGTT:

• Fasting Plasma Glucose (FPG): 5.1 to 6.9 mmol/L (92 to 125 mg/dL)
• 1-Hour Plasma Glucose: >= 10.0 mmol/L (180 mg/dL)
• 2-Hour Plasma Glucose: 8.5 to 11.0 mmol/L (153 to 199 mg/dL). Fasting glucose >= 7.0 mmol/L or 2-hour glucose >= 11.1 mmol/L instead meets the diabetes-in-pregnancy range and requires prompt specialist management.

Maternal-Fetal Morbidity

Maternal glucose readily traverses the placenta via facilitated diffusion (GLUT transporters), whereas maternal insulin does not cross. Uncontrolled maternal hyperglycemia drives fetal pancreatic beta-cell hyperplasia and secondary hyperinsulinism (the Pedersen hypothesis). Insulin functions as a potent fetal anabolic growth hormone, yielding:

• Fetal Macrosomia & Asymmetric Overgrowth: Disproportionate deposition of adipose tissue around the fetal shoulders and abdomen (abdominal circumference > 90th percentile), predisposing to severe shoulder dystocia, clavicular fracture, and brachial plexus avulsion (Erb-Duchenne palsy).
• Neonatal Metabolic Collapse: Immediate post-delivery neonatal hypoglycemia resulting from abruptly severed maternal glucose supply in the presence of autonomous fetal hyperinsulinism.
• Respiratory Distress Syndrome (RDS): Elevated fetal insulin levels directly inhibit cortisol-mediated fibroblast-pneumocyte factor production, arresting pulmonary surfactant synthesis in type II pneumocytes despite biological term maturity.
• Polycythemia & Hyperbilirubinemia: Fetal tissue hypoxia drives erythropoietin secretion, causing severe neonatal polycythemia (hematocrit > 65%), microvascular sludging, and hyperbilirubinemia.
• Hypertrophic Cardiomyopathy: Transient hypertrophy of the interventricular septum, potentially obstructing the left ventricular outflow tract.

Therapeutic Protocols & Glycemic Targets

First-line therapy consists of Medical Nutrition Therapy (MNT) with a registered dietitian, structuring complex carbohydrates across three main meals and two to three snacks, combined with 30 minutes of daily moderate-intensity walking. Capillary blood glucose is monitored four times daily (fasting and 1 or 2 hours postprandially). The target glycemic levels are:

• Fasting Plasma Glucose: < 5.3 mmol/L (95 mg/dL)
• 1-Hour Postprandial: < 7.8 mmol/L (140 mg/dL)
• 2-Hour Postprandial: < 6.7 mmol/L (120 mg/dL)

If lifestyle modifications fail to maintain target glucose levels within 1 to 2 weeks (>= 20% of readings above target), pharmacological therapy is indicated. Metformin (500 mg orally once or twice daily, titrated up to 2,000 mg daily) is widely utilized as an effective oral agent. If metformin is insufficient, contraindicated, or if marked fetal abdominal circumference overgrowth is evident on ultrasound, subcutaneous insulin is initiated (neutral protamine Hagedorn [NPH] or detemir as basal insulin; regular human insulin or rapid-acting insulin aspart/lispro as preprandial boluses).

Clinical & Biophysical Fetal Surveillance

Symphysiofundal Height (SFH)

Symphysiofundal height measurement remains the primary clinical screening tool for fetal growth abnormalities in resource-conscious health settings. Using a non-elastic tape measure, distance is recorded along the midline of the maternal abdomen from the superior margin of the pubic symphysis to the uppermost palpable border of the uterine fundus, with the metric markings placed facedown to avoid examiner bias. Between 20 and 36 weeks of gestation, the SFH in centimeters corresponds to gestational age in weeks within +/- 2 to 3 cm:

• SFH > 2 to 3 cm Below Dates: Suggests fetal growth restriction (FGR), oligohydramnios, transverse fetal lie, or mistaken dating.
• SFH > 2 to 3 cm Above Dates: Suggests fetal macrosomia, polyhydramnios, multiple pregnancy, pelvic masses (leiomyoma), or mistaken dating.

Any significant SFH discrepancy warrants urgent formal ultrasound biometry measuring biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) to derive the Estimated Fetal Weight (EFW).

Cardiotocography / Non-Stress Test (NST)

The Non-Stress Test monitors fetal heart rate (FHR) acceleration in response to spontaneous fetal movement, reflecting an intact, non-acidotic autonomic nervous system. Over a standard 20-minute window, criteria are:

• Reactive (Normal): Presence of >= 2 accelerations peaking at least 15 bpm above baseline and lasting >= 15 seconds from baseline to return (the "15 x 15 rule" for >= 32 weeks; for 28 to 32 weeks, "10 x 10" is accepted), with normal baseline rate (110 to 160 bpm) and moderate variability (6 to 25 bpm).
• Non-Reactive: Fewer than 2 accelerations over 20 minutes. The tracing is immediately extended to 40 minutes to account for the physiological fetal sleep cycle (fetal quiet sleep typically lasts 20 to 40 minutes). Persistent non-reactivity requires progression to formal biophysical profile testing.

Biophysical Profile (BPP - Manning Score)

The Manning BPP integrates acute and chronic markers of fetal hypoxemia by combining ultrasound observation over 30 minutes with an external cardiotocograph. Each parameter receives 2 points if normal and 0 points if abnormal (maximum score: 10/10):

1. Non-Stress Test: Reactive tracing with >= 2 accelerations (+2).
2. Fetal Breathing Movements: At least one episode of continuous fetal breathing lasting >= 30 seconds (+2).
3. Gross Body Movements: At least three discrete body or limb movements (+2).
4. Fetal Tone: At least one episode of active limb/spine extension with prompt return to flexion, or opening and closing of a fetal hand (+2).
5. Amniotic Fluid Volume: Single deepest vertical pocket (DVP) of fluid >= 2 cm free of umbilical cord loops (+2). (Amniotic Fluid Index [AFI] 5 to 25 cm is also used).

Biophysical activities develop sequentially in embryonic life and are extinguished in reverse order under progressive asphyxia: fetal tone arises first (at 8 weeks) and is the last to vanish in severe hypoxemia; fetal breathing appears at 21 weeks and disappears early under mild hypoxemia. Amniotic fluid volume reflects chronic uteroplacental perfusion: chronic hypoxemia redirects fetal cardiac output away from kidneys to the brain and heart, diminishing fetal urine production and producing oligohydramnios.

• Score 8/10 or 10/10 with Normal Fluid: Reassuring. Oligohydramnios requires further assessment and possible delivery regardless of the total score.
• Score 6/10: Equivocal; repeat within 24 hours when preterm and otherwise stable; consider delivery at term or with additional concerns.
• Score <= 4/10: Abnormal and concerning for fetal compromise; obtain urgent specialist assessment. Delivery is usually indicated, but management before 32 weeks depends on repeat surveillance, gestational age and the clinical situation.

Umbilical Artery Doppler Velocimetry in Fetal Growth Restriction

Umbilical artery Doppler velocimetry measures resistance within the fetoplacental microcirculation. In a healthy placenta, low vascular resistance yields high continuous forward flow throughout diastole, reflected by a low systolic-to-diastolic (S/D) ratio and low pulsatility index (PI).

In placental insufficiency and fetal growth restriction (FGR), progressive microvascular obliteration of tertiary placental villi elevates downstream resistance, producing sequential hemodynamic deterioration:

1. Elevated Resistance: Decreased end-diastolic velocity yielding elevated S/D ratio and PI (> 95th percentile).
2. Absent End-Diastolic Flow (AEDF): Absent diastolic flow indicates severe placental resistance. Increase Doppler surveillance to 2 to 3 times weekly and intensify CTG monitoring, often as an inpatient. If stable, plan delivery at 33 to 34 weeks; deliver earlier for deterioration.
3. Reversed End-Diastolic Flow (REDF): Reversed diastolic flow indicates severe placental insufficiency and a high risk of fetal compromise. Admit to a specialist centre, give antenatal corticosteroids if preterm delivery is expected, and monitor CTG at least once or twice daily. If stable, delivery is generally planned at 30 to 32 weeks; abnormal fetal testing or maternal deterioration can require earlier birth. Give magnesium sulfate for neuroprotection when delivery before 32 weeks is likely. Cesarean delivery is usually appropriate with these major Doppler abnormalities, according to the full clinical picture.
4. Ductus Venosus Doppler: An absent or reversed a-wave is a late warning of fetal cardiovascular compromise. Specialist early-FGR protocols combine this with gestational age and computerized CTG to decide delivery; it is not an isolated universal hours-to-delivery rule.

Antenatal Routine Booking & Surveillance Protocols