The intrauterine contraceptive device and hydatidiform mole: a negative association.

None of the 135 hydatidiform moles studied (40 complete and 95 partial) occurred in women currently wearing the IUCD. In the control series of 1,244 non-molar spontaneous abortions, conception took place with the IUCD in situ in 48 women (3.87%). The difference between the observed number of molar pregnancies with the IUCD in situ, i.e., 0, and the "expected" number, i.e., 4.64 (3.87%) was statistically different (p less than 0.05). This difference could not be explained by such uncontrolled confounding variables as maternal age, menstrual age of the abortions, prior pregnancy loss, gravidity, ethnicity or contraceptive practices. It is suggested that the IUCD selectively suppresses the development of molar pregnancies. The theoretical and practical implications of this observation are discussed.