Maternal lifestyle risk factors and human embryonic morphologic development using 3D ultrasound: a population-based prospective cohort study.

study questionAre periconception maternal modifiable lifestyle factors (i.e. smoking, alcohol consumption, caffeine intake, folic acid supplement use, and physical activity) associated with embryonic morphologic development and growth in a large population-based cohort study? SUMMARY ANSWER: Inadequate folic acid supplement use and insufficient serum folate levels were associated with delayed embryonic morphologic development and reduced growth, while no associations were observed for smoking, alcohol, caffeine intake, or physical activity. WHAT IS KNOWN ALREADY: Modifiable maternal lifestyle factors during the periconception period may influence embryonic growth and development. Prior studies suggest associations between smoking, folic acid use, and first trimester growth, but evidence on morphologic development remains limited. STUDY DESIGN, SIZE, DURATION: This study was embedded in the Generation R Next Study, a population-based periconception cohort in Rotterdam, the Netherlands, conducted between 2017 and 2021. Of the 2173 included spontaneous singleton pregnancies, 993 had reliable pregnancy dating, 3D ultrasound data up to 10 + 2 weeks of gestation, and available information on periconception lifestyle risk factors. PARTICIPANTS/MATERIALS, SETTING,

methodsEmbryonic development and growth were assessed in vivo at 7 and 9 weeks of gestation using 3D transvaginal ultrasound and virtual reality techniques. Morphologic development was determined using the Carnegie staging system based on limb position, embryonic curvature, and brain morphology; crown-rump length (CRL) was used to assess growth. Periconception lifestyle factors, including smoking, alcohol and caffeine intake, physical activity, and folic acid supplement use, were assessed using early pregnancy questionnaires. Linear mixed models were used to examine the association between lifestyle factors and embryonic Carnegie stages and CRL. Analyses were adjusted for gestational age at ultrasound, maternal age, ethnicity, education level, parity, fetal sex, and the other lifestyle factors. MAIN RESULTS AND THE ROLE OF CHANCE: Inadequate folic acid supplement use was associated with a 0.51-day delay in embryonic development and a 0.72-mm reduction in CRL (-1.6%) at 10 + 2 weeks of gestation. Insufficient serum folate levels (<25.5 nmol/l) were associated with a 1.01-day developmental delay and a 1.24-mm reduction in CRL (-3.7%). No significant associations were observed for smoking, alcohol or caffeine intake, or physical activity. Results remained robust after adjustment for confounders. LIMITATIONS, REASONS FOR CAUTION: Lifestyle exposures were self-reported, which may have introduced recall or social desirability bias. Gestational age determination was based on the last menstrual period, which can result in dating discrepancies due to variability in cycle length or inaccurate recall, but strict inclusion criteria were applied to minimize misclassification. The relatively healthy study population could limit the generalizability of our results to higher-risk groups. WIDER IMPLICATIONS OF THE

findingsOur findings emphasize the importance of initiating folic acid supplementation in the preconception period to ensure sufficient maternal folate levels, which may support optimal embryonic morphologic development and growth during the first trimester. These results reinforce public health recommendations advocating timely folic acid supplementation to promote healthy early embryonic development. STUDY FUNDING/COMPETING INTEREST(S): The Generation R Next Study is financially supported by the Erasmus University Medical Centre Rotterdam, the Erasmus University Rotterdam, and the Netherlands Organization for Health Research and Development. R.G. received funding from the Netherlands Organization for Health Research and Development (NWO, ZonMw VIDI 09150172110034, and NWO, ZonMW, grant number 05430052110007) and an European Research Council Starting Grant (ERC-2024-STG 101161004). V.W.V.J. received a grant from the Netherlands Organization for Health Research and Development (NWO, ZonMw 05430052110007) and a European Research Council Consolidator Grant (ERC-2014-CoG-648916). The authors declare no conflicts of interest. TRIAL REGISTRATION NUMBER: N/A.