Introduction Nutrition is important in a healthy pregnancy, but little is known about the impact of multivitamins (MV) on the survival of the fetus.

Methods We related periconceptional MV use to early (<20 weeks) and late (≥20 weeks) fetal death. At recruitment, women in the Danish National Birth Cohort (n=35 897) reported the number of weeks of MV use during a 12 week periconceptional period. Information about lifestyle factors came from a later telephone interview. Cox regression was used to estimate HR for the association between MV use and fetal death with follow-up starting at 8 completed weeks of gestation. Intensity of preconception use (6 weeks before conception) and postconception use (6 weeks after conception) were categorised as use in 1–2, 3–4, and 5–6 weeks. No use at any time of these weeks was reference.

Results Compared to women with <2 weeks of preconception MV use, risk of early fetal death increased with increasing intensity of use (adj. HRs 1.18 [0.84 to 1.67] and 1.31 [1.03 to 1.66] for 3–4 and 5–6 weeks of use, respectively). Risk of early fetal death was also increased in women with the highest intensity of post-conception use (adj. HR 1.84 [1.11 to 3.03] while for late fetal death, we identified a reduced risk with high intensity exposure (adj. HR 0.56 [0.32 to 0.97] for 5–6 weeks of use).

Conclusion While these results indicate that postconception use of MV has a preventive effect on late fetal death, MV use was consistently associated with a higher rate of early fetal death.