In chronic hypertension, it is the Dopplers at 35 weeks, not the centile

Design

Secondary analysis of a prospective cohort with propensity-score matching, 1:2

Population

1258 singleton pregnancies with chronic hypertension scanned at 35+0 to 36+6 weeks

Primary outcome

Development of superimposed preeclampsia

Effect

Preeclampsia in 18.6% overall; excess confined to the 64 cases with abnormal Dopplers, who delivered 1.7 weeks earlier than matched controls

Among 1258 pregnancies with chronic hypertension scanned routinely at 35+0 to 36+6 weeks, 167 had an estimated fetal weight below the tenth centile and 64 of those also had abnormal Dopplers. After propensity-score matching against 334 controls, only the group with abnormal Dopplers went on more often to superimposed preeclampsia, by every definition tested.

They also delivered 1.7 weeks earlier, were induced more often, had more caesareans and had more neonatal unit admissions. The small-for-dates group without Doppler abnormality differed only marginally — 0.7 weeks earlier delivery and more small babies — and showed no excess preeclampsia.

The practical consequence is that the 35 to 36 week scan in these women should not stop at a centile. Uterine, umbilical and middle cerebral artery indices separate a fetus that is constitutionally small from a placenta that is failing, and it is the second group whose mothers are about to declare themselves.

• Request Dopplers, not just biometry, at the 35 to 36 week scan in chronic hypertension.
• Where Dopplers are abnormal, raise the frequency of maternal blood pressure and proteinuria checks rather than waiting for symptoms.
• Plan the delivery conversation early in this group; they delivered about 1.7 weeks sooner.
• A small fetus with normal Dopplers does not by itself justify escalated maternal surveillance.
• Record which definition of superimposed preeclampsia your unit uses; the finding held across all three.

Why it matters

It separates the small baby that needs watching from the mother who is about to become ill.

Don't overread it

The finding is from one cohort at 35 to 36 weeks and has not been reproduced earlier in pregnancy.

The statistics, in plain English

This is a propensity-score-matched secondary analysis, which balances measured confounders such as parity, body mass index and previous preeclampsia but can do nothing about unmeasured ones. The matched design is why the two comparisons can be read against each other: the Doppler-abnormal group and the centile-only group were each matched to their own controls, so the contrast between them is the informative part. With 64 Doppler-abnormal cases, subgroup estimates are small-sample and the authors ask for replication at earlier gestations.

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