ObjectiveTo examine inequalities in preconception health between migrant women in potentially vulnerable situations and non-migrant women.DesignNational cross-sectional study.SettingData from the National Health Service (NHS) Maternity Services Data Set (MSDS) version 1.5, using data submitted by NHS maternity services in England.ParticipantsAll 652,880 women with an antenatal booking appointment between 1/4/2018 and 31/3/2019 were included. Data regarding migration status were available for 66.2% of the study population (n=432,022).Outcome measuresPrevalence of preconception indicators were compared between probable migrants (those with complex social factors and English not their first language), possible migrants due to English not being a first language (without complex social factors), possible migrants due to complex social factors (who speak English as a first language) and unlikely migrants (those who speak English as a first language without complex social factors). Complex social factors include recent migrants, asylum seekers or refugees, difficulty reading or speaking English; alcohol and/or drugs misuse; all those aged under 20; and/or experiencing domestic abuse. Odds ratios were calculated comparing preconception indicators among those identified as migrants compared to unlikely migrants.ResultsWomen identified as probable migrants (n=25,070) had over twice the odds of not taking folic acid before pregnancy and of having their first antenatal booking appointment after the recommended 10 weeks gestation compared to unlikely migrants (n=303,737), after adjusting for area-based deprivation level, mothers age at booking, number of previous live births and ethnicity (odds ratio 2.15 (95% confidence interval 2.06 to 2.25) and 2.25 (2.18 to 2.32) respectively). Probable migrants had increased odds of previous obstetric complications and being underweight at booking, but lower odds of recorded physical and mental health conditions (apart from diabetes and hepatitis b), smoking and obesity in unadjusted and adjusted analyses.ConclusionsInequalities between migrant women in potentially vulnerable situations and non-migrants exist across many preconception indicators. Findings highlight the opportunity to improve preconception health in this population in order to reduce health inequalities and improve perinatal and neonatal outcomes.