Congenital abnormalities of the uterus, or congenital müllerian anomalies, include a spectrum of uterine abnormalities caused by abnormal embryologic fusion and canalization of the Müllerian ducts to form a normal uterine cavity. Essentially, development of the uterus begins with two tube-shaped structures known as the Müllerian ducts which later come together to form the uterus; for some, the connection of these two ducts is incomplete or results in an abnormal uterus. These anomalies are often asymptomatic and unrecognized, but have a reported prevalence of approximately 2-4% in reproductive age women, and up to 5-25% in women with adverse reproductive outcomes. However, the true incidence is unknown as screening for uterine anomalies is typically only performed in women with certain adverse pregnancy outcomes or abnormal gynecologic symptoms.
The presence of a uterine anomaly appears to increase the risk of adverse pregnancy outcomes such as preterm birth, fetal growth restriction, malpresentation, cesarean delivery, and preeclampsia. A uterine septum also appears to increase the risk of early pregnancy loss. There is an association between uterine anomalies and renal (kidney) anomalies as they have related embryologic precursors.
Classification of uterine anomalies usually follows the 1988 American Fertility Society classification and includes hypoplasia/agenesis, unicornuate, didelphys, bicornuate, septate, arcuate, and DES drug-related. In some instances, uterine anomalies fall between two categories and are classified as hybrid or complex. Nonsurgical diagnosis of uterine anomalies can be made by ultrasound, MRI, or hysterosalpingogram. Saline-infusion-sonohysterogram (SIS) is a highly reliable diagnostic study with over 95% accuracy.
Among congenital uterine anomalies, the following are the most common:
- Septate: the uterus is divided into two sections by a band of muscle or tissue
- Bicornate: also known as “heart-shaped,” this abnormality results in two cavities within the uterus
- Didelphys uterus: also known as a “double uterus,” women with this abnormality have two cervices and two separate uterine cavities
- Unicornate uterus: this abnormality is the result of only one half of the uterus developing
- (Retroverted or tipped uterus): This is not a uterine anomaly and is considered a normal variant (like being left-handed or right-handed). A retroverted uterus tips backward. It is seen in about 20-25% of women.. It does not typically cause any gynecologic or pregnancy complications, but a small percentage may have more pain in the beginning of pregnancy while the uterus grows and then pushes against the sacral bone. Rarely, the uterus gets “stuck” as it tries to grow out of the pelvis and needs to be manipulated by a doctor to do so.
Women with uterine abnormalities should be followed closely in pregnancy due to the increased risk of complications. Such complications could include premature birth or diminished fetal growth during pregnancy. Women with a septate uterus may have an increased risk of early miscarriage if the pregnancy implants (by chance) onto the septum itself, instead of the uterine wall. Women with uterine abnormalities may also be more likely to have babies in the breech position during labor or require a c-section. Throughout pregnancy, your obstetrician or maternal fetal medicine specialist will inform you of what you can expect throughout pregnancy and labor.
In some cases, the uterus can be repaired with surgery. For example, those with a septate uterus may undergo surgery to potentially reduce the risk of miscarriage.
In addition to these concerns regarding pregnancy, women with uterine abnormalities should have a kidney ultrasound to ensure they have two normal-appearing kidneys.
Maternal Fetal Medicine blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!