During the period 1967-1976, prospectively collected data were available in the Finnish Register of Congenital Malformations on the contraceptive usage of 3,002 mothers of children with malformations detected at birth, as well as of time-matched and place-matched control mothers. The distributions of the various types of malformations were similar among contraceptive users (immediately prior to or during the pregnancy) and nonusers. The total incidences of various methods of contraception were also similar among mothers of malformed children and the control mothers. The risk ratio method for matched pairs allowed us to evaluate the strength of the observed negative correlation concerning oral contraceptives. Thus, we could exclude with 95% confidence any effect larger than 5% of oral contraceptives on the incidence of visible malformations.
PIP: A nationwide register of congenital malformations, estimated to cover 65-70% of all defects detected at birth, was maintained in Finland. For the period 1967-76, collected data were available on the contraceptive usage of 3002 mothers of children with malformations detected at birth. The register is based on a matched-pair approach with much of the information collected prospectively during antenatal visits. The register was investigated to determine whether there is an association between OC (oral contraceptive) use prior to or during early pregnancy and malformations in the babies. The distributions of various types of malformations were similar among OC users and nonusers; there was a slightly lower incidence of central nervous system anomalies and a higher incidence of oral clefts among IUD users. The total incidence of various methods of contraception were also similar among mothers of malformed children and the control mothers. It is concluded, and the study results confirm findings from other such studies, that there is no more than a 5% effect of OC use on the incidence of visible malformations, at a 95% confidence level.