Teratogenicity of progestogens given during the first trimester of pregnancy.

Possible teratogenic effects of exogenous progestational agents given during early pregnancy were investigated by a controlled historic prospective study of 2754 infants born to mothers who had bled during the first trimester of pregnancy. The study group consisted of 1608 newborns whose mothers had been treated with progestogens (mostly medroxyprogesterone acetate) beginning in the first trimester. The control group comprised 1146 infants of untreated mothers. All newborns were subjected to thorough examination during the first days of life, with special attention to detection of various malformations classified according to the different anatomic systems. No significant difference was found between the treated and the control groups with respect to malformations in any of the systems examined. The overall rate of malformations was 120 per 1000 in the study group and 123.9 per 1000 in the control group. Major malformations occurred at rates of 63.4 and 71.5 per 1000, respectively. The study thus fails to demonstrate an increase in teratogenicity after administration of gestagens during the first trimester of pregnancy.