Geographic variation in spontaneous preterm birth incidence at the province and municipal level in the Netherlands: A population registry based study

Preterm birth (PTB), defined as birth before 37 completed weeks of gestation, is a major public health concern with long-term health consequences. Risk factors for (spontaneous) PTB (sPTB) include medical, lifestyle, demographic, environmental, and obstetric factors. Low socioeconomic status (SES) and late initiation of antenatal care (ANC) are known contributors, but their municipal-level impact remains understudied. This study explores the distribution of sPTB across Dutch provinces and municipalities and assesses the role of SES and ANC in regional disparities to inform targeted, place-based interventions. Data from the Netherlands Perinatal Registry (PERINED) on 952,262 singleton pregnancies (2016-2021) were analyzed. Incidence rates of PTB and sPTB were calculated per province and municipality. Logistic regression was used to calculate crude and adjusted sPTB odds ratios across 12 provinces and 364 municipalities. Adjustments were made for SES, late ANC, and risk factors including parity, maternal age, ethnicity, fetal sex and urbanisation level. The incidence of sPTB was 3.6%, with substantial variation across provinces and municipalities (range 2.1-6.6%). Regional differences were partly influenced by SES, late initiation of ANC, and maternal and pregnancy-related characteristics, but persisted after adjustment. Additional adjustment for urbanisation attenuated these regional disparities. There are marked geographic disparities in PTB and sPTB odds across the Netherlands, not fully explained by SES or late ANC. Further research into local environmental or contextual factors is needed to inform targeted strategies for improving perinatal health outcomes.