Uterine Anomalies Affecting Fertility
More couples where the female partner has a uterine anomaly are seeking care in the current clinical practice of reproductive medicine. This apparent increase is not due to a change in the prevalence of uterine anomalies in the population but is due the availability of better imaging techniques of the uterus itself and the practice of assisted reproductive technology (ART). In this era of ART, there has been more attention paid to the impact of mullerian anomalies and their potential therapies on the outcomes of these assisted pregnancies.
The true prevalence of uterine anomalies in the population is unknown. It is insufficient to consult the older medical literature because of inconsistent diagnostic techniques utilized in the past and the heterogeneity of the subject populations that were studied. With the general wide spread use of transvaginal ultrasound and hysterosalpingograms (HSG) in reproductive-age women, increased detection of uterine anomalies in the general population can be expected, especially in the infertile and recurrent miscarriage subgroups. Following detection of uterine anomalies by ultrasound and HSG, the availability of magnetic resonance imaging (MRI) and three-dimensional ultrasound (3D US) should increase the accurate diagnosis of these anomalies as diagnostic criteria are applied more consistently.
The prevalence of major uterine anomalies is estimated to be 5% in the general population, 2-3% in fertile women, 3% in infertile women and 5-10% in the recurrent miscarriage population. Historically, the most common uterine malformation has been the bicornuate uterus. However, a study of 127 uterine anomalies showed the prevalence of the arcuate uteri and partial uterine septum were more frequent than bicornuate uteri. A similar distribution of uterine anomalies has been found by 3D US, which is a new technology that has been found to be comparable with older studies that utilized HSG and laparoscopy as the gold standard.
In 1998, the American Society for Reproductive Medicine (international organization of fertility experts) classified mullerian anomalies in an attempt to provide clinicians with a tool to better document the actual anomaly and subsequently follow their patients in regards to both conception and pregnancy outcome.
Table 1 is a compilation of data from selected studies that have examined pregnancy outcomes for each specific uterine anomaly. (REFERENCE: Reproductive Outcomes of Uterine Anomalies. Lin PC. J of Women's Health 2004: 13; 33-9. )
Table 1: Summary Of Reproductive Outcomes In Uterine Anomalies
Overall, data is limited in the reproductive outcome of uterine anomalies undergoing IVF because of the relative infrequency of such uterine anomalies. However, this situation may change in the near future as access to ART and IVF pregnancy rates improve.
In general, uterine anomalies present some difficulty in pregnancy retention and overall pregnancy outcome with natural conception and ART.
Arcuate uterus probably has no impact on reproductive capacity. The uterine septum is more definitively associated with recurrent miscarriage and, unlike the bicornuate uterus; surgical correction is technically easier and less morbid. Therefore, in the face of suspect data, surgical repair for the infertile couple with no previous pregnancies seems reasonable. The bicornuate uterus appears to suffer from an increased miscarriage rate and preterm delivery and the surgical repair is more extensive.
The didelphic uterus was originally thought to have no impact on reproductive outcome. Re-evaluation of the literature shows that it does increase preterm deliveries and miscarriage rates. Like the unicornuate uterus, the didelphic uterus has an increased risk of malpresentation and cesarean section for dystocia. Patients with a unicornuate uterus have the poorest outcome: higher miscarriage rates, higher ectopic rates, higher preterm delivery rates and lower live-birth rates.
In general, the role of IVF needs to be better evaluated with studies looking at a greater number of subjects. IVF pregnancy rates appear to be decreased not because of decreased number or quality of eggs obtained but rather due to the uterine anomaly itself. Resulting implantation rates and clinical pregnancy rates are still uncertain but may be reduced by 50% compared to women undergoing IVF without anomalies.