Approximately 50-75% of pregnancies end in spontaneous abortion. Most of these pregnancy losses are unrecognized because they occur before or at time of the next expected menses. Of the clinically recognized pregnancies, approximately 15-20% are lost in the first trimester.

Vaginal spotting is relatively common and thus not necessarily indicate a miscarriage. Spotting may also be caused by intercourse, vaginal or cervical lesions, infection or increased friability of the cervix. Heavier menstrual type bleeding occurs in approximately 20% of women during the first trimester of the pregnancy, and of those patients, approximately one-half will miscarry.

There is no evidence that bed rest is helpful. Continued activity will not influence fetal outcome. Likewise, there is no evidence that maternal trauma to the abdomen or falls can cause first trimester spontaneous miscarriages.

(1) An ultrasound demonstrating absence of fetal heart activity is indicative of a miscarriage. With a transvaginal ultrasound, fetal heart activity should be detected around 6-7 weeks gestational age. (2) Declining serial quantitative human chorionic gonadotropin hCG (blood pregnancy test) levels are indicative of fetal demise.

Evaluation is not recommended for a single first trimester spontaneous abortion if the woman is otherwise healthy. Most spontaneous abortions are the inevitable consequence of morphologic or cytogenetic abnormalities of the embryo or fetus. Prospective studies have demonstrated that approximately 80-90% of women who have had a single first trimester abortion deliver a viable infant in the next pregnancy. One should resume a normal menstrual cycle 2-6 weeks after the miscarriage.