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Recurrent Spontaneous Abortion and Recurrent Pregnancy Loss -- Miscarriage

Spontaneous abortion occurs in 15% of diagnosed pregnancies in women who are 15-44 years of age. Recurrent spontaneous abortions occur in about 3-4% of these women, defined as the loss of three or more consecutive pregnancies. Most spontaneous abortions occur because of abnormalities in the fetus. Almost 70% of first-trimester abortuses, 30% of second-trimester abortuses, and 3% of stillbirths.

Recurrence Risk

The risk of pregnancy loss increases from 15-20% in the first pregnancy to 40% after one spontaneous abortion, but does not increase thereafter. The prevalence of spontaneous abortion increases with increasing maternal age, although not with gravidity. The risk begins to increase rapidly at age 35 years. The risk of spontaneous abortion at age 40 years is approximately twice that at age 20 years. Although one might suspect that the reason for this increase is the known rise in aneuploid conception with increasing maternal age, this does not wholly account for the rapid rise in spontaneous abortion.



Anatomic Anomalies

Müllerian Fusion Defects

Müllerian defects of all types are associated with a higher incidence of pregnancy loss. The septate uterus, the most common anatomic abnormality, carries a risk of 70% spontaneous abortion in the first trimester. This is believed to be due to the relatively less vascular nature of the implantation site. A higher term pregnancy rate has been reported in women who underwent surgical resection. Abdominal metroplasty is reserved for a bicornuate uterus and carries the risk of postoperative adhesion formation. For properly selected patients in whom other causes of repeated abortion have been excluded, a significant improvement in fetal salvage may be expected.

Intrauterine Synechiae

Intrauterine synechiae (Asherman's syndrome) may cause oligomenorrhea, infertility, or spontaneous abortion. Adhesions may follow overzealous curettage of the uterus during the postpartum period, intrauterine surgery (eg, myomectomy), or endometritis. Dense, avascular adhesions may interfere with implantation or placentation. As many as 90% of patients conceive after hysteroscopic lysis of the adhesions, with the subsequent spontaneous abortion rates ranging from 6% to 21%. However, no randomized data exist to confirm the efficacy of hysteroscopic lysis of adhesions in preventing subsequent spontaneous abortion. Because the procedure entails little risk in the hands of skilled surgeons, the possible benefits warrant hysteroscopic lysis in couples experiencing repeated losses.


Uterine leiomyomas are usually multiple and may contribute to pregnancy loss, but the pathophysiology is unknown. Location, rather than size, of the leiomyoma is probably the most important factor. Submucous leiomyomas may result in fetal loss through several theoretical mechanisms: 1) endometrial thinning over the surface of the myomas may impair decidualization and implantation; 2) necrosis within the myomas (red degeneration) from hormonally stimulated growth exceeding the blood supply may lead to uterine contractions and fetal expulsion; or 3) the myomas may encroach on the space required by the developing fetus.

Therapeutic efficacy of myomectomy has not been documented in controlled trials, but has been suggested by surgical cohorts with increased postoperative term pregnancy rates. As in incomplete müllerian fusion, careful patient selection is important and the increased risk of mechanical infertility.

Endocrine Abnormalities

Thyroid Disease

The theory that thyroid disorders cause spontaneous abortion is now disproved. Although there is no need to screen asymptomatic patients with spontaneous losses for thyroid disease, irregular menses and amenorrhea remain indications for testing. Serum tests to diagnose thyroid disorders are commonly available and thwart the need to treat empirically "subclinical" disease.

Diabetes Mellitus

When inadequately controlled, type 1 diabetes (formerly referred to as insulin-dependent diabetes mellitus) may increase the risk of spontaneous abortion. However, euglycemic patients with diabetes mellitus do not have an increased risk of pregnancy loss. Therefore, routine screening for diabetes mellitus in patients with recurrent spontaneous abortion is not warranted.

Luteal-Phase Defect

The luteal-phase defect is presumably responsible for abnormal development of the endometrium required for implantation and placentation. The luteal-phase defect results either from a deficient secretion of progesterone or a poor endometrial response to adequate levels.