Fetal assessment, prenatal screening and counselling — formative SAQs

SAQ 1 — No-call cell-free DNA result in a higher-risk pregnancy (20 marks, ~15 minutes)

A 37-year-old woman at 11 weeks gestation, body mass index 34, has a cell-free DNA screen that reports a no-call result due to low fetal fraction. She asks whether that means the baby is fine and no further testing is needed. She lives two hours from the nearest diagnostic service and has intermittent phone reception. [1] [16]

Questions

1. Define screening versus diagnostic testing and explain why this distinction matters now. (3 marks) [1]
2. Explain why a no-call cell-free DNA result is not equivalent to a low-risk result. (4 marks) [1] [16]
3. Outline the management options for a no-call result and the factors that guide the choice between repeat screen and diagnostic testing. (5 marks) [1] [11]
4. Give four elements of non-directive counselling you would use with this woman at this visit. (4 marks) [6] [18]
5. Describe four system actions that ensure she is not lost to follow-up given rural geography and access barriers. (4 marks) [18]

Model answer anchors

1. Screening estimates a probability of a condition; diagnostic testing confirms or excludes it. A no-call screen is neither, so the distinction determines whether to repeat, diagnose or surveil rather than reassure. [1]
2. A no-call reflects low fetal fraction, which is itself associated with raised maternal body mass index, early sampling, aneuploidy and fetal growth restriction; the no-call is therefore an informative signal carrying its own risk, not a low-risk result. [1] [16]
3. Options are repeat cell-free DNA, diagnostic testing (chorionic villus sampling or amniocentesis by gestation), and detailed ultrasound with surveillance. Higher pre-test probability favours diagnostic testing over simple repeat screen; quoted procedure-related risk should be contemporary. [1] [11] [12]
4. A no-call is not a normal result; what the next options are and their risks; that the choice is hers with support; clear written information; teach-back; named contact for questions. [6] [18]
5. Book before discharge; dual contact details and a backup number; interpreter if needed; transport and leave-from-work support; active chase list; written and verbal plan with a named owner. [18]

SAQ 2 — Small fetus with abnormal Doppler (20 marks, ~15 minutes)

A 28-year-old woman at 29 weeks gestation has an estimated fetal weight below the third centile on international standards, with absent end-diastolic flow on umbilical artery Doppler. She smokes and has chronic hypertension. She asks what will happen next and whether the baby will need to be delivered early. [8] [9]

Questions

1. Distinguish a constitutionally small but healthy fetus from true fetal growth restriction, and state how Doppler helps. (4 marks) [8]
2. Interpret the absent end-diastolic flow finding and explain its significance for surveillance and delivery timing. (4 marks) [9]
3. Outline the stepwise surveillance and delivery-planning pathway, including the role of gestational age. (6 marks) [8] [9]
4. Describe the role of antenatal corticosteroids and magnesium sulfate when delivery timing is brought forward, gated by gestation. (3 marks) [13]
5. Give three paediatric and neonatal planning actions that must occur before delivery for this infant. (3 marks) [18]

Model answer anchors

1. A constitutionally small fetus has normal growth velocity and normal Doppler reflecting a normally developed placenta; true growth restriction reflects uteroplacental insufficiency with abnormal Doppler, maternal disease or both. Doppler is the key discriminator. [8]
2. Absent end-diastolic flow indicates severe uteroplacental insufficiency with high vascular resistance; it is associated with fetal compromise and drives more intensive surveillance and earlier delivery than isolated small size. [9]
3. Confirm with repeat biometry against international standards, classify as early-onset placental growth restriction, intensify Doppler surveillance (umbilical artery and, where indicated, middle cerebral artery and ductus venosus), admit or review frequently, and time delivery by gestation and Doppler trend, balancing prematurity against intrauterine compromise. [8] [9]
4. When delivery before the gestational threshold for corticosteroid benefit is anticipated, give antenatal corticosteroids for fetal lung maturation; at very preterm gestations, magnesium sulfate provides fetal neuroprotection. Both are gated by gestational age and local protocol. [13]
5. Neonatal team alert, planned place and time of delivery with neonatal capability present, and a defined postnatal plan for thermoregulation, feeding, glucose and developmental surveillance coordinated by the paediatric medical home. [18]