Women who supplement with a small amount of vitamin C during the second half of pregnancy reduce their risk of one contributor to premature birth, according to the American Journal of Clinical Nutrition (2005;81:859–63).

The end of pregnancy and the beginning of the birth process is marked by rupture of the walls (membranes) of the sac that holds the growing fetus and the amniotic fluid. A healthy pregnancy usually lasts about 40 weeks. Premature birth occurs when the membranes rupture and birth begins before 37 weeks of pregnancy. Smoking, vaginal infection, and poor maternal nutrition can all increase the risk of premature rupture of the membranes (PROM). PROM occurs in 10 to 20% of pregnancies worldwide and is the most common cause of premature births. Babies born prematurely face many health risks: their underdeveloped lungs do not function properly, they are highly susceptible to infections, and they have difficulty nursing.

Studies have suggested that inadequate levels of vitamin C in the cells of pregnant women might be linked to increased PROM risk. Vitamin C, an antioxidant nutrient found in fruits and vegetables, plays an important role in the production and repair of connective tissues throughout the body and is believed to be critical to the maintenance of the fetal sac membranes. In one study, women with high dietary intake of vitamin C were less likely to experience PROM than women with low intake. The effect of vitamin C supplementation on risk of PROM has not been previously studied.
In the current study, 120 healthy women who were less than 20 weeks pregnant were randomly assigned to receive either 100 mg of vitamin C per day or placebo. Each woman was evaluated upon entry to the study and every four weeks from week 20 of their pregnancy until delivery. PROM incidence was 74% lower in the women taking vitamin C than in the women receiving placebo (7.69% versus 24.5%). The incidence of premature births was also lower in the vitamin C group than in the placebo group (13.4% versus 24%); however, this 44% reduction in risk was not statistically significant because of the small number of people studied.

The results of this study suggest that supplementing with vitamin C can reduce the risk of PROM. Since PROM is involved in more than 40% of all premature births, it is possible that small amounts of supplemental vitamin C might help prevent premature births. A larger study is needed to determine this more definitively.

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