The incidence of Mullerian anomalies in the general population has been found to be about 2 to 3%, but 14% in women with RPL. The septate uterus is by far the most common. Abnormalities other than those induced by DES generally occur before the 12th week of fetal life, as a result of medial fusion defects. The standard classification system currently in use is that of the American Society of Reproductive Medicine:
There is an increase in SAB in women with unicornuate and didelphic uteri. With unicornuate uteri, the risk of SAB is 44% and with didelphic uteri, the risk is 36%. Less than 1% of fertile women have bicornuate uteri, with the reported risk of SAB ranging from 24 to 84%. It is difficult to determine the risk with accuracy since most studies do not carefully distinguish between bicornuate and septate uteri. Although the two conditions may have identical appearances on hysterosalpingography (HSG), many studies base the diagnosis on HSG findings alone. The septate uterus is the most common congenital uterine anomaly and is reported to have the highest risk of SAB, over 60%. Mullerian anomalies are diagnosed and distinguished from one another by various modalities including HSG, ultrasonography, MRI, laparoscopy, and hysteroscopy. Transvaginal ultrasonography is capable of defining the abnormality, with more invasive means such as laparoscopy and hysteroscopy sometimes being required.
Most women with uterine fibroids have successful pregnancies, however, the effect of the fibroids on the course of pregnancy and the risk of loss depends on the size, number, and location of the fibroids. Submucosal and intracavitary fibroids are felt to induce the greatest risk of loss, possibly due to pressure effect on the endometrial cavity and alteration of blood flow.
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