Periconceptional multivitamin use and risk of preterm or small-for-gestational-age births in the Danish National Birth Cohort

Abstract

Background: The intake of periconceptional multivitamins may decrease the risk of preterm births (PTBs) or small-for-gestational-age (SGA) births.

Objective: We related the timing and frequency of periconceptional multivitamin use to SGA births and PTBs and its clinical presentations (ie, preterm labor, premature rupture of membranes, and medical induction).

Design: Women in the Danish National Birth Cohort (n = 35,897) reported the number of weeks of multivitamin use during a 12-wk periconceptional period. Cox regression was used to estimate the relation between any multivitamin use and PTBs (<37 wk) or SGA births (birth weight adjusted for gestational age >2 SDs below the mean on the basis of fetal growth curves). The timing (preconception and postconception) and frequency of use were also analyzed. Regular users (4-6 wk) and partial users (1-3 wk) in each period were compared with nonusers.

Results: The association between periconceptional multivitamin use and PTBs varied according to prepregnancy overweight status (P-interaction = 0.07). Regular preconception and postconception multivitamin use in women with a prepregnancy BMI (in kg/m(2)) <25 was associated with reduced risks of a PTB (HR: 0.84; 95% CI: 0.73, 0.95) and preterm labor (HR: 0.80; 95% CI: 0.69, 0.94). No similar associations were shown for overweight women. The adjusted risk of an SGA birth was reduced in multivitamin users regardless of their prepregnancy BMI (HR: 0.83; 95% CI: 0.73, 0.95), with the strongest association in regular users in the postconception period.

Conclusion: Regular periconceptional multivitamin use was associated with reduced risk of SGA births and PTBs in nonoverweight women.

FIGURE 1.

Periconceptional exposure period. LMP, last menstrual period; LMP-4, 4 wk before the LMP; LMP+2, 2 wk after the LMP; LMP+8, 8 wk after the LMP.

FIGURE 2.

Rates of preterm (A) or small-for-gestational-age (SGA) (B) births according to patterns of periconceptional multivitamin (striped bars) and folate-only use (gray bars) compared with nonusers (dashed line). For each 6-wk preconception or postconception period: +, partial use (1–3 wk of use); ++, regular use (4–6 wk of use); -, no use. *Comparison of preterm birth rate was significantly different from that of nonusers, P < 0.05 (crude Cox regression results).