The Contribution of Hypertensive Disorders of Pregnancy to Neonatal Unit Admissions and Iatrogenic Preterm Delivery at < 34 Weeks' Gestation in the UK: A Population-Based Study Using the National Neonatal Research Database.

Objectives: The objectives of this study were to (i) quantify the contribution of maternal hypertensive disorders of pregnancy (HDP) to iatrogenic preterm birth (PTB) and neonatal unit (NNU) admissions < 34 weeks and (ii) describe short-term population-level outcomes for HDP infants, exploring ethnic disparities and comparing outcomes by HDP exposure.

Design: Retrospective population-based study using the National Neonatal Research Database.

Setting: England and Wales.

Population: Infants born < 34 weeks and admitted to NNU 2012-2020.

Methods: Descriptive statistics, linear and logistic regression models to compare outcomes between groups.

Main Outcome Measures: Survival to discharge with/without comorbidity.

Results: 122 228 infants met inclusion criteria. Where collected, 49 839/114 164 (43.7%, 95% CI 43.4%-43.9%) of infants had an iatrogenic PTB. HDP was recorded in 16 510/122 228 (13.5%) of all infants and 13 560/49 839 (27.2%) of iatrogenic PTBs. HDP and/or foetal growth restriction (FGR) were recorded in 24 124/49 839 (48.4%) of iatrogenic PTBs. Singleton HDP infants < 10th BWC had ≥ 90% survival to discharge from 28 weeks' gestation, versus from 26 weeks' gestation for those born ≥ 10th BWC. In extreme preterm HDP infants (< 27 weeks), 27.3% of infants < 10th BWC died compared to 15.2% of those ≥ 10th BWC. Survival without comorbidity was ≥ 90% from 32 weeks' gestation in HDP infants across BWC.

Conclusions: These contemporaneous population-level data show that almost one in two PTB < 34 weeks' gestation are iatrogenic, with HDP and/or FGR being the major contributors to iatrogenic prematurity. This has substantial implications for strategies to reduce preterm birth in the UK and internationally. The data further inform antenatal and at-birth counselling of HDP-exposed infants.