22.1 Prenatal Care: Diagnosis of Pregnancy, Maternal Physiology, Dating, Nutrition & Supplements, Screening Tests and the DOH Antenatal Package

Why this area matters

TOS area B asks you to:

• recognize the burden of unplanned pregnancy;
• describe the physiologic changes of pregnancy, prenatal nutrition and supplements, routine laboratory tests and the schedule of prenatal consultations;
• recognize signs of normal and abnormal fetal development;
• counsel against toxicants, pollutants and unsafe foods;
• choose screening and diagnostic tests that detect fetal anomalies and maternal risks.

Early, regular antenatal care is the foundation of the DOH maternal health program. Complications found early (anemia, hypertension, diabetes, infection, malpresentation) can be managed or referred before labor. Unplanned pregnancies, especially among adolescents, often start care late, so every visit is also a chance to plan the next pregnancy.

Diagnosis of pregnancy

• hCG is made by the syncytiotrophoblast. It roughly doubles every 48 hours in early viable pregnancy and peaks at 8 to 10 weeks.
• A gestational sac is seen on transvaginal ultrasound at about 4.5 to 5 weeks, a yolk sac at about 5.5 weeks and cardiac activity at about 6 weeks.

Maternal Physiologic Adaptations to Pregnancy

Pregnancy triggers profound systemic anatomical and physiologic alterations designed to support embryonic growth, optimize fetal oxygenation, and prepare the maternal organism for parturition.

Cardiovascular Alterations

• Plasma Volume and Hematology: Maternal blood volume increases by 40% to 50% above non-pregnant levels, beginning as early as 6 weeks of gestation and peaking between 28 and 32 weeks. Erythrocyte mass increases by only 20% to 30%, driven by elevated erythropoietin. This disproportionate fluid expansion results in physiologic dilutional anemia of pregnancy. Normal hemoglobin thresholds shift downward: the lower limit of normal is 11.0 g/dL in the first and third trimesters, and 10.5 g/dL in the second trimester.
• Cardiac Output: Cardiac output ($CO = HR \times SV$) increases by 30% to 50%. In early pregnancy, this rise is primarily driven by an increased stroke volume (SV). Later in gestation, resting heart rate increases by 10 to 15 beats per minute (bpm). Cardiac output peaks immediately postpartum due to autotransfusion from the contracted uterus and relief of inferior vena cava compression.
• Systemic Vascular Resistance (SVR) and Blood Pressure: High levels of circulating progesterone, along with enhanced endothelial release of nitric oxide and prostacyclin ($PGI_2$), induce widespread vascular smooth muscle relaxation. Consequently, SVR falls by up to 30%. Maternal blood pressure declines early in the first trimester, reaching a nadir at 24 to 28 weeks of gestation (diastolic pressure typically drops by 10 to 15 mmHg), before gradually returning to non-pregnant baseline levels at term.
• Supine Hypotensive Syndrome: In the supine position after mid-gestation, the gravid uterus compresses the inferior vena cava (IVC) and descending aorta. This reduces venous return to the right atrium, precipitously lowering cardiac output and causing maternal hypotension, diaphoresis, syncope, and fetal bradycardia. It is rapidly alleviated by placing the patient in the left lateral decubitus position.

Respiratory Adaptations

• Progesterone exerts a direct stimulatory effect on the medullary respiratory center, increasing respiratory drive.
• Ventilatory Mechanics: Diaphragmatic elevation of up to 4 cm occurs as the gravid uterus expands, reducing Functional Residual Capacity (FRC) and residual volume by approximately 20%. Compensatory flaring of the lower ribs broadens the subcostal angle and increases chest circumference.
• Minute Ventilation and Acid-Base Status: Maternal respiratory rate remains essentially unchanged, but tidal volume ($V_T$) increases by 30% to 40%. This drives a 30% to 50% increase in minute ventilation, causing chronic physiologic hyperventilation. Arterial blood gas (ABG) analysis in normal pregnancy reveals a compensated chronic respiratory alkalosis:
  • Arterial pH: 7.40 to 7.45
  • $p\text{CO}_2$: 27 to 32 mmHg
  • Plasma $\text{HCO}_3^-$: 18 to 22 mEq/L (due to compensatory renal excretion of bicarbonate)
  • $p\text{O}_2$: 100 to 105 mmHg
• This physiologic maternal hypocapnia creates a steep transplacental carbon dioxide concentration gradient, facilitating the diffusion of $CO_2$ from fetal blood into maternal circulation.

Renal and Urinary Adaptations

• Renal Hemodynamics: Renal plasma flow increases by up to 75%, and Glomerular Filtration Rate (GFR) rises by 50% starting in the first trimester. This marked hyperfiltration lowers normal serum markers:
  • Normal pregnancy serum creatinine: about 0.4 to 0.8 mg/dL; a value above about 0.9 mg/dL is abnormal for pregnancy and suggests renal disease.
  • Normal pregnancy Blood Urea Nitrogen (BUN): 8 to 10 mg/dL.
• Anatomical Dilation: Progesterone-induced smooth muscle relaxation, combined with mechanical compression by the dextrorotated gravid uterus at the pelvic brim, causes physiologic hydroureter and hydronephrosis (predominantly right-sided). This urinary stasis significantly increases the risk of progression from asymptomatic bacteriuria to acute pyelonephritis.
• Glucosuria and Proteinuria: Filtered glucose load exceeds tubular reabsorptive capacity, producing mild physiologic glucosuria. Normal urinary protein excretion rises up to 300 mg per 24 hours.

Hematologic and Hemostatic Changes

• Pregnancy represents an acquired hypercoagulable state:
  • Marked increases occur in fibrinogen (Factor I, doubling to 400-600 mg/dL), Factors VII, VIII, IX, X, XII, and von Willebrand factor.
  • Protein S levels decrease, and resistance to activated protein C increases.
  • Fibrinolytic activity is suppressed antepartum, recovering rapidly after placental separation.
• These changes serve as an evolutionary adaptation to prevent exsanguination during placental detachment, but they elevate the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE) fivefold antepartum and up to twentyfold in the postpartum puerperium.
• Mild leukocytosis is normal during gestation (white blood cell count 5,000 to 12,000/$\mu\text{L}$), rising up to 25,000/$\mu\text{L}$ or higher during active labor and the immediate postpartum period without signifying infection.

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Antenatal Care, Dating & Clinical Surveillance

Comprehensive antenatal care aims to detect risk factors, screen for congenital and maternal disease, and optimize maternal and neonatal outcomes.

Gestational Age Dating and Clinical Assessment

• Naegele's Rule: In women with regular 28-day menstrual cycles, the Estimated Date of Confinement (EDC) is calculated from the first day of the Last Normal Menstrual Period (LNMP): $\text{EDC} = \text{LNMP} + 7\text{ days} - 3\text{ months} + 1\text{ year}$
• Ultrasonic Dating: First-trimester transvaginal ultrasound measuring the crown-rump length (CRL) is the single most accurate method for establishing gestational age (margin of error $\pm 3\text{ to } 5\text{ days}$). When ultrasound dating differs from menstrual dating by more than 5 days before 9 weeks, or more than 7 days between 9 and 14 weeks, the ultrasound date supersedes the LNMP.
• McDonald's Rule (Fundal Height Measurement): The distance from the superior border of the pubic symphysis to the top of the uterine fundus correlates with gestational age in centimeters between 20 and 36 weeks (gestational age in weeks $\approx$ fundal height in cm $\pm 2\text{ cm}$):
  • 12 weeks: Uterus palpable just above the pubic symphysis.
  • 16 weeks: Fundus midway between the pubic symphysis and the umbilicus.
  • 20 weeks: Fundus at the level of the umbilicus (20 cm).
  • 36 weeks: Fundus at the xiphoid process.
• Leopold's Maneuvers: A systematic four-step abdominal palpation protocol performed after 28 weeks:
  1. First Maneuver (Fundal Grip): Identifies which fetal pole occupies the uterine fundus. The fetal head is hard, round, smooth, and ballottable; the breech is softer, irregular, nodular, and non-ballottable.
  2. Second Maneuver (Umbilical Grip): Palpates the lateral uterine walls to locate the fetal back (firm, convex, smooth resistance) and fetal small parts (irregular, nodular extremities).
  3. Third Maneuver (Pawlik's Grip): Grasps the lower uterine pole above the pubic symphysis using the thumb and fingers of one hand to determine whether the presenting part is engaged within the pelvic inlet.
  4. Fourth Maneuver (Pelvic Grip): The examiner faces the patient's feet and presses deep into the lower quadrants toward the pelvic inlet to confirm presentation, assess the degree of cephalic descent, and identify the cephalic prominence.

Evidence-Based Antenatal Screening Schedule

• First Trimester (Initial Visit): Complete Blood Count (CBC), blood typing and Rh antibody screen, Urinalysis and quantitative urine culture (screening for asymptomatic bacteriuria), Rubella IgG titer, Hepatitis B surface antigen (HBsAg), rapid plasma reagin (RPR) or VDRL for syphilis, HIV screening.
• 24 to 28 Weeks of Gestation:
  • Screening for Gestational Diabetes Mellitus (GDM) using the 75g 2-hour Oral Glucose Tolerance Test (OGTT).
  • Repeat CBC for maternal anemia screening.
  • Repeat antibody screen in Rh-negative unsensitized women; administer Rho(D) immune globulin (300 $\mu\text{g}$) at 28 weeks.
• 36 to 37 Weeks of Gestation: Universal screening for Group B Streptococcus (GBS, Streptococcus agalactiae) via a single combined swab of the lower vagina and rectum (through the anal sphincter). Intrapartum antibiotic prophylaxis (IV Crystalline Penicillin G 5 million units loading dose, then 2.5-3.0 million units q4h until delivery; or IV Ampicillin 2g loading then 1g q4h) is administered during labor if:
  • Positive GBS rectovaginal screening culture in the current pregnancy.
  • Documented GBS bacteriuria at any time during the current pregnancy.
  • History of a previous infant with invasive early-onset GBS sepsis.
  • Unknown GBS status with risk factors: labor $<37$ weeks, intrapartum fever $\ge 38.0^\circ\text{C}$ ($100.4^\circ\text{F}$), or rupture of membranes $\ge 18$ hours.

The DOH antenatal care package

• Schedule: at least eight antenatal contacts, at least one in the first trimester, two in the second and five in the third. This replaced the older minimum of four visits.
• Records: visits are recorded in the Mother and Child Book. PhilHealth covers antenatal care in accredited facilities.
• Supplements:
  • iron 60 mg elemental with folic acid 400 mcg once daily for 6 months (180 tablets), started as soon as pregnancy is diagnosed;
  • calcium carbonate where dietary calcium is low, which also reduces preeclampsia risk;
  • iodized salt.
  • Folic acid ideally starts before conception to prevent neural tube defects: 400 mcg daily, or 4 mg daily after a previous NTD-affected pregnancy.
• Tetanus-diphtheria (Td) immunization: pregnant women without documented doses get the 5-dose schedule. Two doses at least 4 weeks apart, the second given at least 2 weeks before delivery, protect the newborn against neonatal tetanus.
• Counseling at each visit:
  • danger signs: vaginal bleeding, severe headache or blurred vision, convulsions, fever, severe abdominal pain, reduced fetal movement and leaking of fluid;
  • a birth plan for facility-based delivery with a skilled birth attendant;
  • breastfeeding and postpartum family planning.

Nutrition, weight gain and things to avoid

• Recommended weight gain depends on pre-pregnancy BMI:
  • underweight: 12.5 to 18 kg;
  • normal weight: 11.5 to 16 kg;
  • overweight: 7 to 11.5 kg;
  • obese: 5 to 9 kg.
• An extra 300 kcal per day is needed in the second and third trimesters.
• Foods: avoid alcohol, raw or undercooked meat and eggs, and unpasteurized milk and soft cheese (Listeria, Toxoplasma). Limit large predatory fish because of their mercury. Limit caffeine to about 200 mg per day.
• Toxicants and pollutants:
  • tobacco smoke, including secondhand smoke, causes low birth weight and abruption;
  • lead from batteries and old paint impairs neurodevelopment;
  • mercury from small-scale gold mining and contaminated fish damages the fetal brain;
  • pesticides, solvents and ionizing radiation are other exposures.
• Drugs with known teratogenic effects:
  • isotretinoin: craniofacial and cardiac defects;
  • warfarin: nasal hypoplasia and stippled epiphyses;
  • valproate: neural tube defects;
  • phenytoin: fetal hydantoin syndrome;
  • ACE inhibitors and ARBs: renal dysgenesis and oligohydramnios;
  • tetracyclines: teeth discoloration;
  • methotrexate;
  • thalidomide: limb defects.

Screening for fetal abnormalities

• First-trimester screening (11 to 14 weeks): nuchal translucency plus PAPP-A and free beta-hCG. In trisomy 21, PAPP-A is low and hCG is high.
• Second-trimester quadruple test (15 to 22 weeks): in trisomy 21, AFP and estriol are low while hCG and inhibin A are high. A raised maternal serum AFP suggests an open neural tube or abdominal wall defect, multiple gestation or wrong dates.
• Cell-free DNA testing is the most sensitive screening test for common trisomies.
• Diagnostic tests: chorionic villus sampling (10 to 13 weeks) and amniocentesis (from 15 weeks).
• Anomaly ultrasound at 18 to 22 weeks surveys fetal structure and the placenta. Fundal height that lags by more than 3 cm, or poor weight gain, prompts an ultrasound for growth restriction or oligohydramnios.