Deliver evidence-based antenatal care and routine screening

In one line

Antenatal care is a structured, goal-directed screening and surveillance programme that runs from early booking to delivery; its modern justification is hard-edged — a minimum of eight contacts reduces perinatal mortality compared with the older four-visit model — and in South Africa it is delivered through BANC-Plus, where universal HIV and syphilis screening, early dating, and pre-eclampsia risk assessment with aspirin matter more than the number of visits the woman actually attends.

The groundwork — what a booking history covers, how to date a pregnancy, the normal physiology of the visit — is assumed here. Revise it at the antenatal booking visit. This chapter is about the consultant judgement: which screening tests earn their place and on what evidence, where the major schedule models diverge and why, and how to run a programme that detects the women who will deteriorate before they do.

Mechanism & pathophysiology

Antenatal care does not treat a disease; it converts an asymptomatic population into a screened one, and almost every controversy in the field is a screening-theory problem wearing obstetric clothes. The logic that governs it is the logic of secondary prevention: a test is worth doing only if the condition has a detectable preclinical phase, the test performs adequately in that phase, and acting on a positive result changes outcome. Each routine investigation in pregnancy has to clear that bar, and several historically entrenched ones do not.

The deeper rationale for frequency — the eight-versus-four argument — is a Bayesian one. Pregnancy complications are not static; pre-eclampsia, fetal growth restriction, malpresentation and gestational diabetes declare themselves across the third trimester, so the pre-test probability of finding a serious abnormality rises as gestation advances. That is precisely why the WHO model loads contacts into the third trimester (30, 34, 36, 38 and 40 weeks) rather than spacing them evenly — the surveillance density should track the hazard rate. The four-visit Focused ANC model thinned the late-pregnancy net at the exact point the disease incidence was climbing, which is the mechanistic explanation for the perinatal-mortality signal that eventually overturned it.

Dating sits upstream of everything. An accurate gestational age, established by first-trimester crown–rump length, is the denominator for every later judgement: whether growth is restricted, whether labour is preterm or post-term, whether a screening result is interpretable. Get the dates wrong and every downstream surveillance decision inherits the error — a falsely "post-term" pregnancy induced unnecessarily, or a genuinely growth-restricted fetus reassured as small-for-dates because the menstrual dates were optimistic. The accuracy of CRL (±5–7 days to 13⁺⁶ weeks) versus the much wider error of later biometry or recalled last menstrual period is the reason early booking is the single highest-leverage act in the schedule.

Risk stratification is the organising principle that makes a one-size schedule safe. The model assumes a low-risk population by default and uses the booking assessment to pull out the women who do not belong in it — prior pre-eclampsia, prior stillbirth, chronic hypertension, diabetes, significant medical disease, HIV, multiple pregnancy — and route them to a more intensive, often specialist-led, pathway. The midwife-led "normal" track and the consultant-led "high-risk" track are not two services but two arms of one triage system, and the booking visit is the triage point. Stratification is also not a one-time act: a woman can enter the low-risk track and earn her way out of it at any contact — a rising blood pressure, a lagging fundal height, a new medical diagnosis — which is why the schedule re-screens rather than simply re-visits.

The final mechanistic point is that screening tests have characteristics, and a consultant reasons in those terms rather than treating a test as a binary truth. Symphysis–fundal height has poor sensitivity for growth restriction; a normal smear in a woman with a visible cervical lesion is a false reassurance; a single non-reactive HIV test at booking does not exclude an infection acquired in the third trimester. The discipline is to know each test's blind spot and to cover it — with serial measurement, a lower threshold for definitive imaging, and the scheduled repeat test — rather than to trust a single negative result to clear a whole pregnancy.

Assessment

The booking contact is the most consequential of the schedule and should happen early — NICE asks for the first appointment by 10⁺⁰ weeks; the WHO model's first contact is within the first trimester (up to 12 weeks). In South Africa the persistent reality is the opposite: a large fraction of women book in the second trimester or later, which forfeits accurate dating, first-trimester aneuploidy screening, and the window in which aspirin prophylaxis works. Late booking is not a footnote in SA practice — it is the dominant failure mode, and counselling the community to present early is a public-health intervention in its own right.

The booking history and examination establish risk, not just background. Beyond standard obstetric, medical, surgical, drug and social history, the assessment is actively looking for the stratifiers above, for previous pregnancy complications that recur, for medications that need review against teratogenicity, and — a mandatory SA element folded into BANC-Plus — sensitive enquiry for intimate-partner violence. Booking BMI, baseline blood pressure and urinalysis anchor later trend interpretation; a single late blood pressure has no baseline to be read against.

Gestational dating is by ultrasound where available: crown–rump length in the first trimester, head circumference in the early second. The dating scan reduces inductions for apparent post-term pregnancy and is the reference against which all later growth assessment is judged. Where early ultrasound is not accessible — a real constraint at many SA district facilities — symphysis–fundal height and clinical estimation carry more weight, and the uncertainty must be acknowledged rather than papered over.

Booking bloods and their interpretation:

• Full blood count / haemoglobin — to detect and treat anaemia (common in SA from iron deficiency, and compounded by HIV); ferritin clarifies iron status where the picture is mixed. Anaemia at booking is both a direct risk (cardiac reserve in the event of haemorrhage) and a marker.
• Rhesus (D) blood group by rapid test identifies the rhesus-negative woman, who then needs atypical-antibody testing at 26, 34 and 40 weeks and anti-D after delivery and after any sensitising event (the SA regimen is set out under management below). A red-cell antibody screen follows a rhesus-negative result rather than being sent routinely for every woman; a clinically significant antibody moves her onto the alloimmunisation pathway developed in Rhesus alloimmunisation. A full ABO group is sent by indication, mainly when transfusion is anticipated, not as a routine booking screen.
• HIV — universal, opt-out testing at booking, then repeated at roughly four-weekly scheduled visits (about 20, 26, 30, 34 and 38 weeks) and again at labour or delivery if negative, because seroconversion during pregnancy is a major driver of vertical transmission in a high-incidence setting. SA uses PVT (prevention of vertical transmission) framing; a positive result triggers ART and the full PVT pathway, not merely a note in the file.
• Syphilis — universal screening at booking, then retested at the same roughly four-weekly scheduled visits as HIV (about 20, 26, 30, 34 and 38 weeks) and at delivery if the first test was negative, because untreated maternal syphilis causes stillbirth and congenital syphilis that early treatment prevents. Point-of-care dual HIV/syphilis rapid tests are increasingly used at SA primary-care antenatal facilities to close the treatment gap that lab turnaround creates, so a reactive result is treated at the same visit.
• Hepatitis B surface antigen — identifies the infant needing birth-dose vaccine ± immunoglobulin and the mother who may need antiviral therapy to reduce transmission.
• Rubella serology — not a routine booking test in the SA public system; it is sent by indication, chiefly contact with a known case. Where a woman is known to be susceptible she is flagged for postpartum vaccination, because the vaccine is live and contraindicated antenatally, closing the loop for the next pregnancy.