the abortional and the teratogenical effects of 17-beta estradiol valerate administration during embryonic development in rats

among the female sexual hormones, the estrogen and progesterone are of significant importance. these hormones are prescribed for the treatment of certain female genital system disorders as well as used in the synthesis of contraceptive drugs. it has been shown that administration of the above hor mones during early pregnancy may produce abortion in early gestational days. in the present investi gation, we have studied the possible abortional and teratogenical effects of a single intramuscular injection of 0.15 mg/kg esteradiol valerate during the first or second half of pregnancy, in rats. the data show that (1) the abortional effects of administration of esteradiol during the first half of pregnancy, in comparison with the control group, is significant. although the injection of this hor mone during the second half of pregnancy does not produce total abortion but there is a reduction in the number of fetuses. therefore, it may be said that with injection of a single dose of hormone dur ing the first half of pregnancy (from day zero to day 10) the chance of abortion is high (in human embryos, this period is about the first four weeks of development). (2) administration of esteradiol may also produce severe fetal abnormalities such as anencephalia, exencephalia, microphthalmia. in addition to the above abnormalities, in the male fetuses, there is also a remarkable defect in the uro genital system.