One hundred-nine pregnant women living in Mexico City who were not taking vitamin supplements were randomly assigned to receive, in double-blind fashion, 100 mg/day of vitamin C or placebo. Treatment was begun in the 20th week of gestation. The mean dietary vitamin C intakes were 63 and 68 mg/day in the placebo and vitamin C groups, respectively. The incidence of premature rupture of the chorioamniotic membranes (PROM) was 24.6% in the placebo group and 7.7% in the vitamin C group (relative risk = 0.26; 95% confidence interval, 0.078-0.837).

Comment: PROM affects 10-20% of all pregnancies. It is the main known cause of preterm delivery and is associated with increased rates of neonatal and maternal morbidity and mortality. Vitamin C plays a role in the synthesis of collagen, which is involved in maintaining the mechanical strength of the chorioamniotic membranes.

The results of the present study indicate that supplementing with 100 mg/day of vitamin C beginning in the 20th week of gestation decreased the incidence of PROM by 74% in Mexican women with borderline-low dietary vitamin C intake. Whether vitamin C supplementation would reduce the incidence of PROM in women whose dietary intake of vitamin C is higher should be the topic of future investigation.

Casanueva E, et al. Vitamin C supplementation to prevent premature rupture of the chorioamniotic membranes: a randomized trial. Am J Clin Nutr 2005;81:859-863.