The use of oral contraceptive just before pregnancy is not associated with an increased risk of major birth defects, says a study.

Although oral contraceptives are widely used and very effective, around nine percent of women become pregnant in the first year of use because of missing a dose, taking the pill with other medications, or illnesses, the study pointed out.

The findings should reassure "women who have a breakthrough pregnancy during oral contraceptive use or even (those who) intentionally become pregnant within a few months of stopping oral contraceptive use (because) any exposure is unlikely to cause her fetus to develop a major birth defect," the researchers said.

To examine the association between oral contraceptive use around the time of conception, and into pregnancy, with major birth defects, the team of US and Danish researchers carried out a large prospective observational study.

All live births, birth defects, and maternal medical conditions were analysed from several national Danish medical registries between 1997 and 2011.

The final analyses included 880,694 liveborn infants, 2.5 percent of whom had a major birth defect – like an orofacial cleft or limb defect – within the first year of life.

Findings from the study revealed no increased risk of any major birth defect associated with oral contraceptive exposure.

The prevalence of major birth defects, per 1, 000 births, was consistent across each group of people that the researchers considered — 25.1 percent for never users, 25 percent for oral contraceptive use more than three months before pregnancy, 24.9 percent for oral contraceptive use within three months before pregnancy, and 24.8 percent for oral contraceptive use after pregnancy.

The study was published in the journal The BMJ.