The number of people adhering to a strict plant-based diet is increasing globally. Adequate maternal nutrition during pregnancy is essential for fetal development, as deficiencies in macro- and micronutrients can cause maternal and neonatal complications. Nutrition can play a role in developing pre-eclampsia, premature birth, and intra-uterine growth restriction. Although there is evidence of nutrient deficiencies in people who follow a strict plant-based diet and the significance of maternal diet for both maternal and fetal outcomes, there has been limited research on the nutritional intake and outcomes of pregnant women on a strict plant-based diet. Additionally, to the best of our knowledge, very limited research has been published on the incidence of pregnancy-induced hypertension, pre-eclampsia, gestational diabetes, or pre-term birth in women on a strict plant-based diet. The relation between these outcomes and nutritional intake/status is also unknown in this specific group of women, even though the number of people with a strict plant-based diet is increasing. The only two studies that studied pregnancy-related outcomes in women on a strict plant-based diet were performed in Israel and were not powered to show statistical differences between a strict plant-based diet and obstetrical outcomes. Additionally, the dietary intake in Israel differs from other parts of the world. Thus, it is impossible to ascertain if the results also apply to a population with a distinct diet. Recently, the Royal Dutch Organization of Midwives (Koninklijke Nederlandse Organisatie van Verloskundigen, KNOV) published 'the guide for vegetarian and vegan diet in pregnancy .' They acknowledge the limited availability of scientific research concerning the strict plant-based diet in pregnancy and the non-existence of data on Dutch pregnant women. They recommend performing additional blood tests for vitamin B12 and D in case of possible nutrition deficiencies in this group of pregnant women. A significantly lower ferritin level is also described in pregnant women on a strict plant-based diet. In conclusion, even though the nutritional intake during pregnancy is vital for both mother and child, the nutritional intake amongst Dutch women on a strict plant-based diet during pregnancy is unknown. Previously published results from Israeli women do not apply to the Dutch population, as nutritional intake differs between countries. The recently published KNOV guide suggests checking vitamin blood levels during pregnancy. To advise and update guidelines for Dutch women on a strict plant-based diet during pregnancy, additional research on nutritional intake and the nutritional status of Dutch women on a strict plant-based diet and to compare this with nutritional status of omnivorous pregnant women is crucial.

The participant will complete a health-related questionnaire. The estimated time required to complete the questionnaire is approximately 10 minutes. Additionally, between 27 and 30 weeks of pregnancy, participants will fill out a three-day food diary. It is estimated that the questionnaire will take approximately 30 minutes to complete each day. Finally, the participants must complete a questionnaire following the baby's delivery. This questionnaire will cover various aspects, such as the pregnancy, delivery, and blood results obtained during pregnancy. The estimated time required to complete the questionnaire is approximately 15 minutes.

During the blood sampling, 10 ml of blood will be collected using an evacuated tube system through venepuncture. Taking blood samples is a routine part of clinical practice, not solely for this study. Pregnant women typically undergo venipuncture between 27 and 30 weeks as part of regular obstetrical care.

The study's results will provide valuable information about the nutritional intake and status of pregnant women who follow a strict plant-based diet compared to those who follow an omnivorous diet during pregnancy. It will also examine the impact of these diets on the health of both the mother and fetus. This information can be used in developing and improving guidelines on diet in pregnancy and may contribute to the health of pregnant women and their newborn future children in the future.