Studies show that choosing a vegetarian or vegan diet can deprive women of all the nutrients they need for a healthy pregnancy.
Many women do not get the essential vitamins they need, and this situation can worsen as more people choose a plant-based diet.
The study examined the vitamin status of 1,729 women from England, Singapore and New Zealand.
He specifically looked for vitamins D, B12 and B6, folic acid and riboflavin in meat and dairy products.
Folic acid and B12 prevent birth defects such as spina bifida, vitamin D helps protect bones, teeth and muscles, and riboflavin supports bone, muscle and nerve development in children. Babies in the womb.
The researchers found that more than 90 percent of the group's marginal or low level of one or more vitamins, many new symptoms of vitamin B6 deficiency at the end of pregnancy.
Keith Godfrey, lead author of the study and Professor of Epidemiology at the University of Southampton, said: "Efforts to reduce our reliance on meat and dairy to achieve net zero carbon emissions will further deprive pregnant women of essential nutrients." Effects on unborn babies.
The group was split into two: an intervention group of 870 women and a control group of 859 women.
Both groups received supplements containing 400 mg of folic acid, 12 mg of iron, 150 mg of calcium, 150 mg of iodine, and 720 mg of beta-carotene.
But the control group's supplement contained 1.8 mg riboflavin, 2.6 mg vitamin B6, 5.2 mg vitamin B12, 10 mg vitamin D, and 10 mg zinc, as well as myoinositol and probiotics.
Blood samples before conception, at the beginning of pregnancy, at the end of pregnancy and six months after giving birth.
A dose of the vitamin found in over-the-counter products before and during pregnancy "significantly reduces deficiency symptoms," researchers said.
They added: "After adding potential micronutrient advocates for additional nutrition, the results suggest that preconceptions and dietary recommendations for pregnancy should be reconsidered and the role of multinutrient supplementation should be considered in women in high-income countries." "
According to NHS England, women trying to conceive should take 400mg of folic acid daily before conception and up to 12 weeks of pregnancy to reduce the risk of problems with their baby's development.
A daily vitamin D supplement is also recommended.
Professor Godfrey added: "Our research shows that almost everyone trying to conceive is deficient in one or more vitamins and this is getting worse as the world moves towards a plant-based diet.
"People think that malnutrition only affects people in underdeveloped countries, but it also affects most women in high-income countries."
Professor Ian Givens, director of the Institute of Food, Nutrition and Health at the University of Reading, said: "This research is timely and should re-evaluate nutrient keys before and during pregnancy.
"In British omnivores, milk, meat and fish provide 80% of vitamin B12 and meat, eggs and fish provide about 65% of vitamin D, although the diet does not provide only three micrograms per day, which means that vitamin D supplementation is necessary. ."
"The authors suggest that the current trend toward at least partial substitution of plant foods for animal foods increases the risk of vitamin B12 and D levels (and other nutrients) in women of childbearing age." Such dietary changes should be considered.
The results were published in the journal PLOS Medicine.
The team was led by scientists from the University of Southampton and supported by the Biomedical Research Center at the National Institute for Health and Care Research (NIHR), the University of Auckland, the National University of Singapore and the Singapore Science, Research and Technology Agency. Technology. .