Do lower antenatal blood pressure cut-offs in pregnant women with obesity identify those at greater risk of adverse maternal and perinatal outcomes? A secondary analysis of data from the UK Pregnancies Better Eating and Activity Trial (UPBEAT).

Abstract

Background: Obesity is a major risk-factor for adverse pregnancy outcomes. While the 2017 American College of Cardiology/American Heart Association (ACC/AHA) classification of normal and abnormal blood pressure (BP) outside pregnancy has been suggested for use in pregnancy, the impact on adverse outcomes has not been examined specifically in women with obesity.

Methods: The UK Pregnancies Better Eating and Activity Trial (UPBEAT) enroled women with a body mass index (BMI) ≥ 30 kg/m². In secondary analyses, maximal antenatal BP was categorised by 2017 ACC/AHA criteria: 'Normal' BP (systolic [sBP] <120 mmHg and diastolic [dBP] <80 mmHg), 'Elevated' BP (sBP 120-129 mmHg and dBP <80 mmHg), 'Stage 1 hypertension' (sBP 130-139 mmHg and/or dBP 80-89 mmHg), and 'Stage 2 hypertension' (sBP ≥140 mmHg and/or dBP ≥90 mmHg, non-severe [sBP 140-159 mmHg and/or dBP 90-109 mmHg] and severe (sBP ≥160 mmHg and/or dBP ≥110 mmHg). Main outcomes were preterm birth, postpartum haemorrhage (PPH), birthweight <10th centile (small-for-gestational age, SGA), and neonatal intensive care unit (NICU) admission. Associations with adverse outcomes were adjusted for UPBEAT intervention, maternal age, booking BMI, ethnicity, parity, smoking, alcohol, and previous pre-eclampsia or gestational diabetes. Diagnostic test properties (positive and negative likelihood ratios, -LR and +LR) were assessed as individual categories (vs. 'Normal' BP), and as threshold values.

Results: Severe 'Stage 2 hypertension' (vs. BP < 160/110 mmHg) was associated with PPH (RR 2.57 (1.35, 4.86)) and SGA (RR 2.52 (1.05, 6.07)) only in unadjusted analyses. No outcomes were associated with 'Stage 1 hypertension' or 'Elevated BP'. All +LR were <5.0 and -LR ≥ 0.20, indicating that no BP threshold was useful as a diagnostic test to detect preterm birth, PPH, SGA, or NICU admission.

Conclusions: Among pregnant women with obesity, we found no evidence that lowering the antenatal BP considered to be abnormal (from 140/90 mmHg) would assist in identifying women and babies at risk.