Abstract

OBJECTIVES: Preterm birth (PTB) is a major public health problem worldwide. It can occur spontaneously or be medically indicated for obstetric complications, such as pre-eclampsia (PE) or fetal growth restriction. The main objective of this study was to investigate whether there is a shared uteroplacental etiology in the first trimester of pregnancy across PTB subtypes. METHODS: This was a retrospective cohort study of singleton pregnancies that underwent screening for preterm PE as part of their routine first-trimester ultrasound assessment at a tertiary center in London, UK, between March 2018 and December 2020. Screening for preterm PE was performed using the Fetal Medicine Foundation algorithm, which includes maternal factors, mean arterial pressure (MAP), uterine artery pulsatility index (UtA-PI) and pregnancy-associated plasma protein-A (PAPP-A). Women with a risk of ≥ 1 in 50 for preterm PE were classified as high risk and offered prophylactic aspirin (150 mg once a day) and serial ultrasound assessments. The following delivery outcomes were evaluated: PTB < 37 weeks, iatrogenic PTB (iPTB) and spontaneous PTB (sPTB). Logistic regression analyses were performed to assess the association of PTB, iPTB and sPTB with an increased risk of preterm PE. A model for prediction of PTB < 37 weeks and < 33 weeks was developed and its performance was compared with that of an existing model in the literature. RESULTS: A total of 11 437 women were included in the study, of whom 475 (4.2%) women had PTB. Of these, 308 (64.8%) were sPTB and 167 (35.2%) were iPTB. Patients with PTB had a higher body mass index, were more likely to be of black or Asian ethnicity, be smokers, have pregestational hypertension or diabetes, or have a history of previous PTB. They also had higher MAP (87.7 vs 86.0 mmHg, P < 0.0001), higher UtA-PI multiples of the median (MoM) (0.99 vs 0.92, P < 0.0001) and lower PAPP-A MoM (0.89 vs 1.08, P < 0.0001) compared to women with a term birth. In women at high risk of PE, the odds ratio for iPTB was 6.0 (95% CI, 4.29-8.43; P < 0.0001) and that for sPTB was 2.0 (95% CI, 1.46-2.86; P < 0.0001). A prediction model for PTB < 37 weeks and < 33 weeks, developed based on this cohort, included previous PTB, black ethnicity, chronic hypertension, diabetes mellitus, PAPP-A MoM and UtA-PI MoM. The performance of the model was similar to that of an existing first-trimester prediction model for PTB < 33 weeks (area under the curve, 0.704 (95% CI, 0.653-0.754) vs 0.694 (95% CI, 0.643-0.746)). CONCLUSIONS: Increased first-trimester risk for uteroplacental dysfunction was associated with both iPTB and sPTB, implying a shared etiological pathway. The same factors used to predict PE risk show acceptable discrimination to predict PTB at < 33 weeks. Women at high risk of uteroplacental dysfunction may warrant additional monitoring and management for an increased risk of sPTB.