An abnormal uterus can sometimes be a risk factor for miscarriage and, in some cases, a cause of recurrent miscarriages. Some uterine malformations are present from birth, and others develop during adulthood. Only some types of uterine malformations increase the risk of miscarriage and require treatment; others may not cause any problems with pregnancy at all.
A uterine septum (septate uterus) is the most common congenital uterine malformation. It is a band of tissue partially dividing the uterus, usually without a good blood supply. If a fertilized egg implants on the septum, miscarriage is likely. Treatment is usually minor surgery. A septate uterus is present from before a woman's own birth.
A bicornuate uterus is a heart-shaped uterus, which is a type of congenital malformation (present from birth). Most women with a bicornuate uterus do not have complications, but in some, a bicornuate uterus can lead to increased risk of preterm labor. A bicornuate uterus is not believed to increase risk of first-trimester miscarriage.
A unicornuate uterus is a horn-shaped uterus. It is a congenital malformation in which one side of the uterus does not develop properly. A unicornuate uterus increases risk of ectopic pregnancy, miscarriage, and preterm delivery.
A didelphic uterus is a "double" uterus, and studies have found that it may increase the risk of preterm delivery and possibly of miscarriage. Didelphic uterus is present from birth.
A T-shaped uterus is another type of congenital malformation of the uterus that is associated with recurrent miscarriages and increased risk of preterm labor. Some women who have a T-shaped uterus do not experience problems, while others do. This specific malformation is sometimes found in women whose mothers took a drug called DES, which was prescribed to some women in the 1960s and 1970s. DES can also cause increased risk of other pregnancy problems.
Cervical insufficiency, or incompetent cervix, means that a woman's cervix begins to dilate too early in pregnancy -- resulting in preterm delivery and sometimes second-trimester pregnancy loss. Cervical insufficiency is not a factor in first-trimester miscarriage. It can be related to congenital malformations or may develop during adulthood.
Many women have uterine fibroids, but some types of fibroids can cause miscarriage or other pregnancy complications. Fibroids can develop during adulthood.
Many women are concerned to hear that they have a tipped (retroverted) uterus, but there is no evidence that a tipped uterus increases the risk of miscarriage or any other problems in pregnancy.