Low Levels of Vitamin B12 in Pregnancy May Increase the Risk of Preterm Birth, Study Finds

Nutrition during pregnancy affects the growing fetus, and identifying appropriate nutritional supplementation in pregnancy has been a hot topic for decades. Vitamin B12 is an essential nutritional component found only in animal-derived products like meat, milk and eggs. Low intake of such products increases the risk of vitamin B12 deficiency. The proportion of pregnant women with vitamin B12 deficiency ranges from a small percentage in some Western countries, like Norway, to over two thirds in developing countries, such as India. In a newly published paper, all previous studies on effects of vitamin B12 levels in pregnancy were evaluated and their results pooled in a meta study. The question asked was whether vitamin B12 deficiency during pregnancy was harmful for the fetus?

Low birth weight and preterm birth are two potentially harmful outcomes of pregnancy. Worldwide, low birth weight and preterm birth are responsible for half of all deaths within the first 28 days after birth. Many studies have evaluated whether low levels of vitamin B12 during pregnancy is associated with low birth weight and preterm birth. Some studies found an association, others have not. In a multi-center study, primarily based at the Yale School of Public Health, Norwegian University of Science and Technology (NTNU), Norway and Erasmus Medical Center, the Netherlands, researchers set out to systematically summarize current knowledge on the topic.

The findings were in the American Journal of Epidemiology. A total of 18 studies from 11 different countries including 11,216 pregnancies were evaluated. Overall, results showed that low levels of maternal vitamin B12 during pregnancy did not affect newborn birth weight. However, vitamin B12 deficient women carried a 21 percent increased risk of preterm birth compared with non-deficient women. These results were similar in high-, low- and middle-income countries.

“These systematic reviews of existing evidence are essential before embarking on massive intervention and supplementation trials and we have done that for vitamin B12,” said

Michael B. Bracken, Ph.D., the Susan Dwight Bliss Professor Emeritus of Epidemiology and former professor of Obstetrics, Gynecology & Reproductive Sciences at the Yale schools of public health and medicine.

The researchers underscore that there may be other reasons for the apparent association between vitamin B12 deficiency and preterm birth. Lead author Dr. Tormod Rogne, PhD candidate at the Department of Public Health and General Practice at NTNU, points out that low levels of vitamin B12 may be associated with other factors, such as undernutrition and poverty, that may affect newborn weight and length of pregnancy. He adds that based on these results, there is insufficient evidence to support routine supplementation of vitamin B12 during pregnancy to improve birth weight and length of gestation. To date, only two small and inconclusive intervention trials have been conducted that evaluate vitamin B12 supplementation during pregnancy and risk of low birth weight and preterm birth. In his opinion, larger trials need to be conducted, and all trials, published and unpublished, will then have to be synthesized in a systematic review. The hope, he concludes, is that their paper will encourage the conduct of these future trials.

Other study authors include senior author Dr. Kari R. Risnes from the Department of Public Health and General Practice at NTNU; Dr. Oscar H. Franco, professor of preventive medicine, Department of Epidemiology at Erasmus MC; Dr. Myrte J. Tielemans, Department of Medical Microbiology and Infectious Diseases at Erasmus MC; and 19 others. The study was funded by NTNU as part of the PhD in Medicine program and supported by the Yale Center for Perinatal Pediatric and Environmental Epidemiology.