Improved Vitamin D Status Is Associated With Lower Incidence of Stillbirth.

Background/aim: Two retrospective studies of prospective cohorts showed doubled odds of birth asphyxia among women with low plasma vitamin D levels, and another study reported a four-fold increased risk of stillbirth. It was not known whether this was related to low sun exposure or to insufficient vitamin D per se. We aimed to assess if it was due to vitamin D status.

Patients and methods: We analyzed the incidence of stillbirth in relation to national vitamin D status for all pregnancies in Finland and Sweden between 1994 and 2021 (n >4.3 million). Due to 50% of the population having low plasma vitamin D, Finland implemented an extensive vitamin D food fortification program in 2003 and doubled it in 2009 because of inadequate results. After 2009, 10% of Finnish women had low vitamin D levels. Stillbirth incidence was related to changes using cross-tabulation with 95% confidence intervals.

Results: The stillborn incidence in Finland decreased from 4.1/1,000 (prior to 2003), to 3.4/1,000 (2004 to 2009), and to 2.8/1,000 after 2009. In the meantime, the Swedish stillbirth rate remained constant at 3.9/1,000 until 2018, when the Finnish food fortification plan was implemented in Sweden. Thereafter, the Swedish stillbirth incidence dropped to 3.2/1,000. The rate of intrahepatic cholestasis of pregnancy, another hypoxic pregnancy complication related to low plasma vitamin D levels, did not drop.

Conclusion: In our large study of national vitamin D food fortification, improved vitamin D status was associated with a lower stillbirth rate in a dose-dependent manner.