“Take vitamins” is a key message in the Beginnings Pregnancy Guide.
The 2007 edition says: Do take your prenatal vitamins
Taking vitamins is a way to make sure your baby gets everything he or she needs to build a strong body. A daily vitamin tablet helps prevent birth defects. Your doctor may order vitamins for you or suggest a brand to buy. Take you prenatal vitamin every day. Do not take extra. More is not better. Page 2
This message has been tested with mothers. We found a nearly universal understanding of “birth defects”, and strong motivation to adopt vitamin-taking for the sake of the baby. Recent research supports the advice to avoid taking more than the recommended daily dose. It is not clear that most prenatal care providers order vitamins or recommend a brand. The evidence is insufficient to discourage vitamin-taking in late pregnancy. But I am alert to further studies on multi-vitamin supplementation in the third trimester. I wonder if the uniquely American policy of multi-vitamin supplementation throughout pregnancy could be contributing to our stubbornly high preterm birth rate.
Based on the latest evidence, for the 2011 edition, I will edit the message to read: Taking vitamins is a way to make sure your baby gets everything he or she needs to build a strong body, especially if you do eat well. Your doctor may order vitamins for you, or look for Prenatal Vitamins at your drug store. Take your vitamin tablet every day. Do not take extra. More is not better.
Summary of Evidence
Folic Acid: In the U.S. and other developed countries, women who might become pregnant are advised to take a folic acid supplement or daily multivitamin before conceiving to prevent neural tube defects* . Starting folic acid before pregnancy is critical since starting supplements after 6 weeks of pregnancy has no demonstrated benefit for preventing neural tube defects; and few women recognize pregnancy before 6 weeks. A large2009 Hungarian study (38,151 newborns) found high doses of folic acid alone during pregnancy, particularly in the third trimester, reduced the risk of preterm birth. A Spanish study found improved verbal and motor function and social competence among 4 year-olds whose mothers took folic acid during pregnancy. It is worth noting that in the Hungarian study, preterm birth was higher if pregnant women took only folic acid, and not other vitamin or mineral supplements during the first and second trimesters.
Multi-vitamins: The evidence on multi-vitamins is less clear. In the U.S., but not in U.K., pregnant women are advised to take a multivitamin supplement throughout pregnancy and breastfeeding. In both countries, prenatal vitamins are widely available over-the-counter and are strongly promoted to pregnant women. As with many elements of prenatal care, the evidence for this recommendation is scant and difficult to translate into practical advice.
Studies show consistently that those who least need supplements (well-nourished mothers) are most likely to take them. Women with low SES, smoking, and high parity are more likely to be undernourished and less likely to take vitamins.
There is some danger that for women who get adequate vitamins and minerals from their diets, supplementation may lead to an excess of nutrients that could cause problems in their babies. For example, supplemental Vitamin E with high dietary intake of Vitamin E was associated with an up to nine-fold increase in risk of congenital heart disease. One study found supplements of Vitamins C & E in addition to adequate dietary intake led to increased risk of premature rupture of membranes.
A 2009 study found any use of vitamins during pregnancy (compared to no use) was associated with slightly decreased odds of miscarriage. The 1997 Camden study found significantly reduced incidence of low birth weight and preterm delivery among U.S. disadvantaged urban women taking multivitamin supplements in the first and second trimester. But a 2010 British study found no association between daily vitamin-taking and birth weight; and reported a three-fold increased risk of preterm birth with daily multi-vitamins in late pregnancy, especially in first-time mothers. This raises concerns about continuing daily multi-vitamin supplements in late pregnancy, and suggests more specific supplementation of only deficient nutrients.
Hasan R, Olshan AF, Herring AH, et al. (2009). Self-reported vitamin supplementation in Early Pregnancy and Risk of Miscarriage. American Journal of Epidemiology 169 (11):1312-1318.
Czeizel AE, Puho EH, Langmar Z et al. (2010). Possible association of folic acid supplementation during pregnancy with reduction of preterm birth: a population-based study. European Journal of Obstetrics and Gynecology and Reproductive Biology148: 135-140. Alwan NA, Greenwood DC, Simpson NAB et al. (2010). The relationship between dietary supplement use in late pregnancy and birth outcomes: a cohort study in British women. BJOG117: 821-829.
Julvez J, Fortuny J, Mendez M, et al. (2009). Maternal use of folic acid supplements during pregnancy and four-year-old neurodevelopment in a population-based birth cohort. Paediatric and Perinatal Epidemiology 23: 199-206