The Contribution of Hypertensive Disorders of Pregnancy to Neonatal Unit Admissions and Iatrogenic Preterm Delivery at < 34+0 Weeks' Gestation in the UK: A Population-Based Study Using the National Neonatal Research Database

Abstract

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⁺⁰ 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⁺⁰ 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⁺⁰ 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.

Keywords: ethnicity; foetal growth restriction; hypertension; neonatal unit; pregnancy; preterm birth.

FIGURE 1

(A, B) Venn diagrams of potential indications/risk factors for preterm birth (PTB) in (A) iatrogenicPTB (iPTB), (B) spontaneous onset PTB, demonstrating HDP/FGR are the most common potential indicators for iPTB and multi‐foetal pregnancy is the most risk factor for spontaneous PTB. (C) Barplot of potential indications for iPTB (non‐mutually exclusive labels) in iatrogenically premature infants (n = 49 839) stratified by gestational age at delivery, demonstrating HDP/FGR is the most common potential indicator for iPTB from 25 week's gestation onwards. APH = antepartum haemorrhage; HDP/FGR = hypertensive disorder of pregnancy/foetal growth restriction; iPTB = iatrogenic preterm birth; MF = multi‐foetal pregnancy; PROM/CHORIO = prolonged or preterm rupture of membranes/chorioamnionitis.

FIGURE 2

Survival with and without comorbidities stratified by (A) antenatal characteristics—gestational age at delivery and HDP status, (B) postnatal characteristics—gestational age at delivery, birthweight centile group and HDP status, in singleton infants from 23 week's gestation. Comorbidity = any of retinopathy of prematurity, severe necrotising enterocolitis or severe brain injury +/− bronchopulmonary dysplasia. BPD = bronchopulmonary dysplasia. Missing denotes infants with missing comorbidity data. For accompanying tabulated data, see Table S3.