O&G SAQs · Antenatal care — timing of birth
Post-term pregnancy — structured SAQ (15 marks)
FRANZCOG-format structured SAQ on post-term pregnancy: definition, the rising stillbirth risk by gestation (Muglu), the Cochrane induction evidence, and structured shared decision-making including the woman who declines induction. Per-sub-part marking rubric included.
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Prompt
You are the antenatal clinic registrar. A 29-year-old low-risk primigravida attends at 41+3 weeks with a reassuring first-trimester dating scan. She has not laboured. She is well, with normal blood pressure, a reactive CTG and normal amniotic fluid volume. She asks whether she has to be induced. (a) Define post-term pregnancy and distinguish it from late-term pregnancy. (2 marks) (b) Quantify how the risk of stillbirth changes with advancing gestation at term, citing the relevant evidence. (3 marks) (c) Outline the evidence for a policy of induction at or beyond 41 weeks versus expectant management. (4 marks) (d) Describe your structured counselling and the management options you would offer this woman, including how you would manage a decision to decline induction. (6 marks)
How this SAQ is marked
Twelve SAQs, 180 marks, two 2-hour papers — roughly 15 marks and 20 minutes each. Marks come from specifics: the definition, the named evidence with its effect sizes, and the structured shared-decision counselling. Write in short labelled points, not prose paragraphs. Answer the sub-part you are asked. [4]
Reveal model answer and mark schemeShowHide
(a) Definition (2 marks)
One mark for the post-term definition, one for distinguishing late-term. [1]
- Post-term (prolonged) pregnancy: 42+0 weeks (294 days) and beyond.
- Late term: 41+0 to 41+6 weeks — a distinct band; do not confuse the two.
- (Optional depth: early term 37+0 to 38+6, full term 39+0 to 40+6, from the term-gestation classification.)[1]
(b) Stillbirth risk by gestation (3 marks)
One mark for the source, one for the direction/magnitude, one for the specific numbers. [1]
- The Muglu 2019 systematic review and meta-analysis (13 cohort studies, 15 million pregnancies, 17,830 stillbirths) quantified the prospective risk of stillbirth by gestational age at term.
- The risk is non-linear: low and nearly flat to 40 weeks, then rising steeply.
- It rises from 0.11 per 1000 at 37 weeks (95% CI 0.07 to 0.15) to 3.18 per 1000 at 42 weeks (95% CI 1.84 to 4.35).
- One additional stillbirth occurs for every 1449 pregnancies (95% CI 1237 to 1747) that continue from 40 to 41 weeks.
- Neonatal mortality also rises: RR 1.87 (95% CI 1.07 to 2.86) for delivery at 42 versus 41 weeks.[1]
(c) Evidence for induction at or beyond 41 weeks vs expectant management (4 marks)
One mark each for the named trial/review, the perinatal death effect, the caesarean effect, and the ARRIVE context. [2]
- Gülmezoglu 2012 Cochrane review (22 trials, 9383 women): a policy of induction at or beyond term versus expectant management.
- Perinatal death: RR 0.31 (95% CI 0.12 to 0.88); NNT 410 (95% CI 322 to 1492) to prevent one perinatal death.
- Caesarean section: RR 0.89 (95% CI 0.81 to 0.97) — induction does NOT raise caesarean, contrary to old dogma. Meconium aspiration syndrome also reduced (RR 0.50); no significant difference in NICU admission.
- ARRIVE (Grobman 2018, NEJM): induction at 39 weeks in low-risk nulliparas gave a lower caesarean rate (18.6% vs 22.2%, RR 0.84) and a primary composite that narrowly met threshold (4.3% vs 5.4%, RR 0.80). Makes 39-week induction a reasonable option after counselling, but generalisability and counselling intensity limit routine rollout.[3]
(d) Structured counselling and management (6 marks)
Two marks for the counselling principles and absolute-number approach; two for the management options; two for managing the decline. [4]
Counselling principles (shared decision-making):
- Present absolute numbers (stillbirth per 1000, NNT 410), not relative risks alone — this honours autonomy.[1]
- Cover both paths honestly: induction reduces perinatal death and does not raise caesarean; expectant management preserves the chance of spontaneous labour but carries the small ongoing risk and surveillance burden.[2]
- Document the discussion, the numbers quoted, and the woman's decision — the post-term stillbirth is a classic litigation trigger.[4]
Management options to offer:
- Membrane sweep from 39 to 40 weeks — reduces the chance of formal induction (aRR 0.73, Boulvain 2020 Cochrane) without raising caesarean or infection.[5]
- Induction of labour at 41+0 — discuss method by Bishop score (unfavourable: prostaglandin or balloon; favourable: amniotomy and oxytocin).[4]
- Expectant management with surveillance, and a documented ceiling (delivery strongly advised by 42+0).[4]
Managing a decision to decline induction:
- Respect a capable, informed decision; the woman may accept, delay or decline.[4]
- Offer enhanced surveillance — at least twice-weekly CTG and ultrasound assessment of amniotic fluid volume from 42 weeks. State explicitly that surveillance lowers but does not eliminate the stillbirth risk.[1]
- Give explicit safety-netting advice to attend immediately if fetal movements reduce.[1]
- Set a documented ceiling and review date; continue to offer the option to change her mind.[4]
References5ShowHide
- [1]Muglu J, Rather H, Arroyo-Manzano D, et al. Risks of stillbirth and neonatal death with advancing gestation at term: a systematic review and meta-analysis of cohort studies of 15 million pregnancies PLoS Med, 2019.PMID 31265456
- [2]Gülmezoglu AM, Crowther CA, Middleton P, Heatley E Induction of labour for improving birth outcomes for women at or beyond term Cochrane Database Syst Rev, 2012.PMID 22696345
- [3]Grobman WA, Rice MM, Reddy UM, et al. Labor Induction versus Expectant Management in Low-Risk Nulliparous Women N Engl J Med, 2018.PMID 30089070
- [4]Keulen JKJ, Bruinsma A, Kortekaas JC, van Dillen J, et al. Timing induction of labour at 41 or 42 weeks? A closer look at time frames of comparison: a review Midwifery, 2018.PMID 30170263
- [5]Finucane EM, Murphy DJ, Biesty LM, et al. Membrane sweeping for induction of labour Cochrane Database Syst Rev, 2020.PMID 32103497