Unicornuate uterus is a type of female genital malformation, and twin pregnancy with the unicornuate uterus is a rare condition that carries considerable risk to the maternal and fetus. Unicornuate uterus that is not combined with a rudimentary uterus with endometrium usually has no obvious clinical symptoms and is often difficult to detect, so the possibility of unicornuate uterus should be considered in women with a history of infertility or adverse pregnancies [2–4]. In this study, the pre-pregnancy diagnosis rate was up to 59.7% (169/283), and early diagnosis of unicornuate or rudimentary uterus is the key to improving pregnancy outcomes. The high pre-pregnancy diagnosis rate may be due to the improvement of the examination methods in recent years, as well as the fact that gynecologists have paid more attention to patients who are infertile or have adverse pregnancies. At present, clinical diagnosis is mainly based on ultrasound, hysterosalpingography, and hysteroscopy or laparoscopy, in addition, MRI, three-dimensional (3D) ultrasonography and 4-dimensional hysterosal⁃pornography(4D-HyCoSy)are gradually being used for diagnosis and further clarification of the type of uterine abnormalities, and it can dramatically improve the accuracy of diagnosis[4, 15–20].
Previous literature has reported that unicornuate uterus is associated with adverse pregnancy outcomes [2]. Our study showed that compared with singleton pregnancy, twin pregnancies with unicornuate uterus were associated with adverse pregnancy outcomes, such as preterm premature rupture of membranes (38.1%,8/21), preterm deliveries (85.7%,18/21), and neonatal intensive care unit (64.3%,27/42), and lower live birth weight. Previous studies also have found that twin pregnancies in unicornuate uterine anomaly were associated with higher risks of preterm delivery, perinatal mortality, and low birth weight [21]. Thus, our findings are in agreement with previously published studies. On the other hand, Ouyang et al. found that selective reduction of twins to a singleton may yield better outcomes in patients with unicornuate uterine anomalies undergoing IVF-ET [21]. Therefore, if unicornuate uterus was found pre-pregnancy, comprehensive counseling about the high risk of twin pregnancy should be provided to the couple, whether or not to have a single embryo transfer or selective reduction to a singleton may be considered in pregnant women with a unicornuate uterus who have twin pregnancies after assisted reproduction to improve pregnancy outcomes.
The incidence of adverse pregnancy outcomes in twin pregnancies with unicornuate uterus was higher than that in the normal uterus or singleton pregnancies in unicornuate uterus, which may be related to the fact that the unicornuate uterus has only 1 uterine artery and some small contralateral arteries supplying blood to the uterus, which affects the perfusion, reduces the muscle, has less uterine muscle mass, an abnormal uterine blood flow, abnormal shape of the uterine cavity, and reduced uterine cavity volume, which is associated with a significantly higher risk for adverse pregnancies in twin pregnancies [4–5].
Twin pregnancy with unicornuate uterus is a rare condition and carries a considerable risk to the maternal and fetal. In our study, patients with unicornuate uterus who detected preconception or during early pregnancy were included in the management of high-risk pregnancies, strengthening supervision and increasing the frequency of prenatal check-ups had been taken into consideration to decrease pregnancy complications and adverse pregnancy outcomes. Because patients with unicornuate uterus may be associated with renal anomalies [3], patients with unicornuate uterus are recommended to undergo routine ultrasound screening of the urinary system and to pay attention to the developmental anomalies of other organs. Meanwhile, ultrasound screening of the fetal system should be strengthened during pregnancy to detect fetal developmental abnormalities in time.
Cesarean section rate for twin pregnancies in unicornuate uterus is as high as 90.5% (19/21), but malpresentation, ICP, and PROM constitute the main indication for cesarean deliveries (12/21,57.1%) in our study. Anomaly uterine pregnancy is not an absolute indication for cesarean section. However, due to the morphological and structural abnormalities of the unicornuate uterus, incomplete development of the myometrium, and poor muscle, the symmetry and polarity of contractions are affected, which may lead to abnormal labor. With IVF-ET twins, the fetus is precious and the patient mostly chooses cesarean section to terminate the pregnancy, so the indications for a cesarean section may be relaxed when terminating the pregnancy. Considering the gestational uterus with abundant blood circulation, we usually do not perform corrective surgery with a rudimentary uterus without endometrium in cesarean section. In recent years, studies have found that vaginal delivery of eligible twin pregnancies is feasible [10, 22–23]. In this study, there was one case of vaginal delivery with a favorable outcome for the mother and child, and no adverse pregnancy outcomes such as uterine rupture or postpartum hemorrhage occurred. This suggests that vaginal delivery in the unicornuate uterus is feasible, however, this is only one case, and the indications for vaginal delivery in the unicornuate uterus with twin pregnancies need to be confirmed by more clinical studies.
In our study, we found that hemorrhage of delivery was higher in unicornuate uterine twin pregnancies than in unicornuate singleton pregnancies and normal uterine twin pregnancies, but there was no statistically significant difference in the incidence of postpartum hemorrhage after the use of powerful drugs to promote uterine contraction and appropriate surgical management. The higher risk of postpartum hemorrhage in twin pregnancies with unicornuate uterus calls for enhanced uterine contractions, improved surgical skills as well as close monitoring of postpartum hemorrhage, and timely intervention measures.
Strength and Limitation
The strengths of our study are that previous studies on unicornuate uterine twin pregnancies were only case reports, and our study of unicornuate uterine twin pregnancies, with a larger number of cases, allowed for a more comprehensive analysis of the perinatal characteristics and the possible adverse pregnancy outcomes of twin pregnancies with unicornuate uterine. However, the main limitation of our study is that the present perinatal study on twin pregnancies in unicornuate uterus is only a retrospective single-center study and more prospective multicenter studies are needed for further confirmation.