Obstetrics – normal pregnancy, prenatal care and physiology
Introduction
This domain tests normal maternal adaptation, the Czech antenatal visit schedule and screening programme, and your ability to read routine laboratory results against pregnancy-specific reference ranges.
Maternal physiology
- Plasma volume rises 40–50% by about 32 weeks while red-cell mass rises only 20–30%, so haemoglobin falls to a dilutional nadir of roughly 105–110 g/L.
- Cardiac output increases 30–50%; systemic vascular resistance falls, so blood pressure is lowest in mid-pregnancy and returns to non-pregnant values at term.
- GFR rises about 50%: creatinine 35–70 µmol/L and urea are lower than outside pregnancy, and mild glycosuria is common.
- Uterine perfusion reaches 500–750 mL/min at term, roughly one fifth of cardiac output.
- Progesterone relaxes smooth muscle: reflux, constipation, right-sided hydronephrosis and a compensated respiratory alkalosis with PCO2 4.0–4.3 kPa.
- Fibrinogen rises to 4–6 g/L and protein S falls; VTE risk is 4–5 times higher.
Antenatal care
- Booking before 11+0 weeks: history, BP, BMI, blood group and RhD, CBC, ferritin, TSH, syphilis serology, HBsAg, HIV, HCV, urine culture, cervical cytology if due.
- Visits every 4 weeks to 28 weeks, every 2 weeks to 36, then weekly or every 3–4 days to delivery.
- Every visit: BP, weight, urine dipstick, fundal height from 24 weeks, fetal heart; CTG only on indication.
Screening
- First-trimester combined screening at 11+0–13+6: nuchal translucency, free β-hCG, PAPP-A, nasal bone; trisomy 21 detection near 90%.
- Detailed anomaly scan at 18–22 weeks; second-trimester serum screening at 16–20 weeks where combined screening was not performed.
- 75-g oral glucose tolerance test at 24–28 weeks.
- RhD-negative women: antibody screen at booking and at 28 weeks, anti-D 250–300 µg at 28 weeks.
- Group B streptococcus swab at 35–37 weeks.
Worked example
A RhD-negative primigravida books at 9 weeks; the antibody screen is negative. At 28 weeks the screen is repeated and is still negative, so routine antenatal anti-D (300 µg, about 1500 IU, intramuscularly) is given. At delivery the cord blood is grouped: if the neonate is RhD-positive she needs a second dose within 72 hours. The antibody screen is always taken before the injection, otherwise passive anti-D masks a genuinely sensitised woman. Had she undergone amniocentesis, or surgical management of a first-trimester loss, a dose would have been due at that time; Kleihauer testing quantifies fetomaternal haemorrhage and large bleeds need extra vials.
Traps
- Labelling Hb 105 g/L at 30 weeks anaemia without a ferritin.
- Using non-pregnant creatinine or TSH ranges (first-trimester TSH upper limit about 2.5–3.0 mIU/L).
- Forgetting the repeat blood group and antibody screen at 28 weeks.
- Withholding an indicated X-ray or CT: the fetal risk from a diagnostic study is far below the risk of a missed diagnosis.