Danish pregnant women are recommended ad daily vitamin D supplement of 10 µg. Despite the fact that 9 out of 10 women take vitamin D supplements, more than 40% of pregnant women are vitamin D deficient, putting them at an increased risk of pregnancy complications like fetal growth restriction and pre-eclampsia. Our hypothesis is that pregnant women would benefit from an increased intake og vitamin D and that an intake of 90µg/day can reduce the prevalence of placenta-related pregnancy complications. Combining a double-blinded randomized trial (10µg vs.90µg) with collection of placental material, we want to test if the prevalence of pregnancy complications is reduced and explore how vitamin D affects placenta to improve our understanding of the disease pathology and risk factors.

As vitamin D (vit-D) is essential for growth and linked to placental function, health authorities recommend a daily 10µg vit-D supplement in pregnancy. Despite the fact that 9 out of 10 women take supplements, more than 40% of pregnant women are vit-D deficient, putting them at an increased risk of pregnancy complications like fetal growth restriction and pre-eclampsia. These conditions affect 6-10 % of all pregnancies, increasing the risk of preterm delivery, perinatal morbidity and mortality. In worse case, preeclampsia may also be fatal for the pregnant women herself. Around 20% of vit-D intake comes from the diet (e.g. fish, egg yolk) and the rest from sun-exposure. However, in Denmark, there is not enough sunlight from October to March to fuel vit-D synthesis underlining the need for supplementation. The high prevalence of vit-D deficiency indicates that current guidelines are not sufficient. Indeed, today´s recommendations date back to a small-scale 1986 Norwegian study not taking into account dietary differences such as the high intake of fish in Norway. Since then, accumulating evidence has linked exposure to pregnancy complications and vit-D deficiency per see to long-term health problems in the affected children. This include a higher risk of asthma, cardiovascular disease, diabetes, obesity schizophrenia, neurodevelopmental problems and multiple sclerosis. Notably, the affected women also suffer an increased risk of disease, e.g. heart disease in later life. Vitamin D supplements in the range of 90-100 µg are safe in pregnancy, but it is not yet known if and to what extent increased vitamin D supplementation prevents pregnancy-related diseases. Combining clinical testing of 90 µg vitamin D supplements, with identification of which placental pathways that are affected by vit-D would considerably improve our understanding of disease pathophysiology and the role of vit-D and improve the health of future generations in an easily implementable way.

Inclusion Criteria:

• All pregnant women attending the nuchal translucency scan in week 11-13 of gestation as part of the national prenatal screening program

Exclusion Criteria:

• Age< 18 years
• Women with calcium metabolism disorders,
• Women who gets doctor prescribed vitamin D treatment
• Women with chronic kidney disease

Treatment is blinded for participants and for the caretakers including nurses, midwifes and obstetricians.

The investigators do not participate in diagnosing patients and are not blinded.