Association between timing of first prenatal visit and preterm birth in a population based ethnically diverse maternal cohort in the UK

Background Timely initiation of prenatal care is critical to maximising positive maternal and infant outcomes. In the UK, women are recommended to start prenatal care by 10 weeks’ gestation. We examined association between timing of first prenatal appointment and prevalence of preterm birth (PTB <37 weeks of gestation) among mothers in an ethnically diverse area in the UK. Methods We analysed routinely collected data on all women who received prenatal care between April 2007 and October 2022 (n=80,508) from a large UK National Health Service maternity unit in an ethnically diverse area. We conducted multiple logistic regression models to examine associations between timing of first prenatal visit and PTB prevalence, including extremely (EPTB <28 weeks), and moderately preterm birth (MPTB 28 to <37 weeks). Findings Gestational week at first prenatal booking appointment was available for 80,176 (99.59%) mothers, of which 62.8%, 28.5% and 8.7% booked at ≤10 weeks, 11-20 weeks and >20 weeks respectively. About one third (31.5%) of all births were to Black Caribbean, Black African, Indian, Pakistani, and Bangladeshi mothers. Prevalence of PTB was 8.5%, including 7.3% MPTB and 1.2% EPTB. Mothers who started prenatal care >16 weeks of pregnancy were more likely to have PTB compared to those who started prenatal care ≤10 weeks [RRR 1.39 (1.28 to 1.50) for MPTB and 3.59 (3.10 to 4.17) for ETPB]. Conclusions Mothers in ethnically diverse areas who started prenatal care late are more likely to have a preterm birth, highlighting need for targeted primary and secondary interventions.