Absent End-Diastolic Flow at 33 Weeks in a Patient Who Wants to Wait Two Weeks
A 34-year-old G2P1 is referred to your unit at 33 weeks 2 days because her fundal height has not changed in 3 weeks. She takes labetalol 200 mg twice daily for chronic hypertension; today's blood pressure is 148/92 mmHg with 1+ protein on dipstick. Ultrasound shows BPD 79 mm (31+4), HC 292 mm (31+6), AC 246 mm (28+5) and FL 63 mm (32+0), with an estimated fetal weight of 1,580 g (below the 5th centile). The umbilical artery pulsatility index is above the 95th centile, with absent end-diastolic flow on two of three waveforms. Middle cerebral artery PI is 1.10, below the 5th centile for gestation. The ductus venosus shows a present a-wave. AFI is 7.2 cm. Her LMP is described as unreliable, and a 21-week scan recorded HC at 21+3 and AC at 20+2. The unit is a 90-minute drive from her home, and she has a 3-year-old with no childcare. She asks whether she can be rescanned in two weeks and keep working until then.
1. Is this a small constitutionally normal fetus or growth restriction? Show how you reconcile the dating and the biometry before deciding anything else.
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The dating question has to be settled first, because an estimated fetal weight centile is meaningless if the gestational age is wrong by two weeks.
The best anchor here is the 21-week scan, not the LMP she describes as unreliable. Second-trimester head circumference is the most robust single dating parameter because it is least affected by growth disturbance, and it was concordant at 21+3. The abdominal circumference at the same scan was already at 20+2, which is a lag of about a week at a stage when growth restriction is just beginning to be expressed. That pattern argues that the dates are broadly correct and that the AC lag is real and early in onset, not a dating artefact.
The biometry pattern matters as well. This is asymmetric: head measurements track around 31+5 while the AC sits at 28+5, a gap of roughly three weeks. Asymmetric growth with an AC-dominant lag points toward placental insufficiency rather than a constitutional small fetus or an early symmetric cause such as aneuploidy or infection, which would usually spare neither head nor abdomen.
One technical caution before accepting the number: the AC plane is unforgiving. A plane that is too low, too high, or taken with rib shadowing or probe compression will underestimate the AC and therefore the EFW. The measurement should be repeated from a true axial plane at the stomach and umbilical vein. If the repeat confirms the lag, the combination of an EFW below the 5th centile, asymmetric biometry, abnormal umbilical Doppler and maternal hypertension makes uteroplacental insufficiency the working diagnosis, not a small normal baby.
2. Grade the Doppler and biophysical findings. What is your management plan for the next 24-72 hours, and what do you tell her about returning to work?
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The Doppler findings are not all equivalent, and grading them correctly is what determines the timeline.
Absent end-diastolic flow in the umbilical artery is a marker of rising placental resistance and places this pregnancy in a high-risk category; it is not an indication for immediate delivery at 33+2 in the absence of other deterioration, but it is an indication for admission and active surveillance. Reduced MCA PI indicates cerebral vasodilatation, or brain sparing. It is a compensatory response and by itself is not a delivery trigger at this gestation. The ductus venosus a-wave is present, which is the reassuring finding here: absent or reversed a-wave flow would signal cardiac decompensation and would push toward delivery within days rather than weeks. AFI 7.2 cm is low-normal and should prompt a check of membrane status and repeat measurement rather than immediate action.
Plan: admit. Give antenatal corticosteroids now, because the chance of delivery within the next week is substantial and the gestational window is closing. Assess for pre-eclampsia with blood pressure monitoring, urine protein quantification and bloods. Start regular CTG assessment, and repeat umbilical artery Doppler every 24-48 hours with growth assessment no more often than every two weeks. Plan delivery around 34 weeks if absent end-diastolic flow persists, sooner if it reverses or if the ductus venosus or CTG deteriorates. Magnesium sulfate for fetal neuroprotection is protocol-dependent at this gestation; discuss it with the unit's obstetric lead.
Work and travel: she should not continue working, and the 90-minute drive is a genuine safety problem if she bleeds or deteriorates. Arrange admission or accommodation close to the unit for the remainder of the pregnancy. Saying 'come back in two weeks' would be wrong on both the Doppler findings and the geography.
3. What findings at the next assessment would make you deliver this baby today rather than continue expectant management?
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The triggers fall into fetal, maternal and acute categories, and each should be named explicitly in the notes so that the next person on call acts consistently.
Fetal triggers: reversed end-diastolic flow in the umbilical artery; absent or reversed ductus venosus a-wave; spontaneous repetitive decelerations or a non-reassuring CTG; a biophysical profile score that falls to 6 or below with an abnormal Doppler; and new oligohydramnios with an AFI below 5 cm or a deepest vertical pocket under 2 cm. Any one of these at 33-34 weeks shifts the balance in favour of delivery, because the risks of continuing outweigh the risks of prematurity now that steroids have been given.
Maternal triggers: blood pressure that becomes severe, symptoms of headache or visual disturbance, falling platelets, rising liver enzymes, or renal impairment indicating pre-eclampsia with severe features. These may require delivery irrespective of the fetal assessment.
Acute triggers: vaginal bleeding, a new tender uterus, or a CTG suggesting abruption. The combination of growth restriction and hypertension makes abruption a real possibility and it can present with relatively little external bleeding.
What should not trigger delivery on its own: a low MCA PI, an AFI of 7 cm, or a single borderline CTG that recovers. Those are reasons to watch more closely, not to deliver.
Counselling point for the patient: with abnormal umbilical Doppler, a vaginal birth is still reasonable, but it requires continuous fetal monitoring, and the neonatal team should be present. Mode of delivery should be decided on obstetric grounds, not on the Doppler result alone.