It found that women who took multivitamins before conceiving were half as likely to deliver their babies before 37 weeks of pregnancy.
However, continuing the multivitamins through the first months of pregnancy appeared to have no influence on the risk of prematurity, write the researchers in the 1 November issue of the American Journal of Epidemiology(160(9):886-92).
Previous research suggests that multivitamin use before and during pregnancy can diminish diet-related deficiencies of certain micronutrients and potentially prevent preterm birth, note the researchers from the University of North Carolina at Chapel Hill.
To assess this association, the authors analysed data from a large study that recruited 2,010 women at 24-29 weeks of pregnancy in four different prenatal care clinics between 1995 to 2000.
While vitamin use before conception reduced the risk of premature birth, prenatal and periconceptional use showed no impact on the likelihood of preterm birth.
The researchers noted that further studies are needed with a larger sample of preconceptional users to confirm their findings.
In the UK about 8 per cent of babies are born prematurely, before 37 rather than the usual 40 weeks of gestation.
Previous research has demonstrated that folic acid, found in multivitamins, helps to prevent birth defects.