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 used in the earlier studies, and the heterogeneity of the subject populations that were studied. However, a recent study indicated that the prevalence of uterine anomalies varies from 0.1% to 10%.1-3 There are various severities of uterine anomalies that range from complete agenesis to different phenotypes. These abnormalities can be diagnosed using a combination of ultrasound, hysteroscopy and/or laparoscopy.2 While müllerian anomalies can be successfully diagnosed using ultrasound, particularly three-dimensional ultrasound.3,4 The American Society for Reproductive Medicine has classified müllerian anomalies in an attempt to provide clinicians with a tool to better document the actual anomaly and to aid subsequent follow-up of patients in terms of conception and pregnancy outcome.5 Although some patients are clinically asymptomatic, müllerian duct anomalies are associated with primary infertility, haematometra and urinary tract anomalies. Normal pregnancies can occur in patients with müllerian duct anomalies, but obstetric complications such as spontaneous abortion, stillbirth and preterm birth are frequent.6,7 Adequate assessment is essential in these patients and could further improve their prenatal outcome. In the present study, we evaluated the obstetric outcome of patients with uterine malformations in comparison with normal pregnancies in China. This study aimed to improve our understanding of the poorly understood outcomes of pregnancies in patients with uterine anomalies and to provide reference statistics that could be used in the counseling of women confronting potentially worrisome pregnancies.
Patients and clinical data
This is a retrospective single-center study that presents a descriptive analysis of the results. Medical charts of all patients referred for uterine anomalies for delivery to the Department of Obstetrics and Gynecology, Peking University Third Hospital between June 1998 and June 2009 were retrospectively reviewed. Uterine anomalies were analyzed after they were classified according to the American Society for Reproductive Medicine,8 either during previous surgery or on sonohysterographic evaluation, laparoscopy with hysterography, or hysteroscopy.
Patients with multiple pregnancies and known congenital and/or chromosomal fetal anomalies were excluded. A total of 270 randomly selected women with a previously confirmed normally shaped uterus (based on pelvic surgery, uterine exploration after delivery or endoscopy for various indications were included as a control group).
Premature delivery was defined as delivery before 37 weeks of gestation. Intrauterine growth retardation was defined as birth weight (g) two standard deviations (SD) below the population mean for gestational age and sex. Live birth was defined as the delivery of a baby after at least 28 weeks gestational age.
Hypertension was defined as blood pressure 140/90 mm Hg or higher in two separate measurements 4 hours apart. Mild hypertension was defined as diastolic blood pressure 90 mmHg or higher and less than 110 mmHg and/or systolic blood pressure 140 mmHg or higher and less than 160 mmHg. Severe hypertension was defined as diastolic blood pressure 110 mmHg or higher and systolic blood pressure 160 mmHg or higher. Gestational hypertension was defined as hypertension that was developed after 20 weeks of gestation without proteinuria. Preeclampsia (PET) was defined as elevated blood pressure and proteinuria of at least 1+ on dipstick; its severity was defined according to the severity of hypertension and/or one of the following: 3+ proteinuria by dipstick, thrombocytopenia 100 000/L or less, elevated liver enzymes, persistent headache, and blurred vision.
Patients were diagnosed as having gestational diabetes (GDM) according to oral glucose tolerance test and were classified according to White's classification. Hydramnios was defined as amniotic fluid index (AFI) more than 25 cm or when a vertical pocket of at least 8 cm was measured or as a subjective estimation of increased amniotic fluid volume. Oligohydramnios was defined as AFI less than 5 mm. Indication for cervical cerclage was clinical. Cerclage was indicated if the uterine cervix was shortened and the internal ostium opened before the 28th week of pregnancy. The study was approved by the Local Ethics Committee of Peking University Third Hospital.
Maternal demographic characteristics, pregnant outcome were compared between women with and without uterine anomalies. Student's t test and analysis of variance (ANOVA) were used to compare means for normally distributed variables. The χ2 and Fisher exact test were used to compare categorical variables. The analysis was carried out using the Statistical Package for Social Sciences (SPSS Inc, Chicago, IL, USA); P <0.05 was considered to be statistically significant.
Incidence and pregnancy complications of uterine anomalies
For the period under study, there were a total of 21 961 deliveries at our hospital, of which 116 (0.45%) were in women with uterine anomalies. A septate uterus was present in 43 (37.1%) and uterus didelphys was in 28 (24.2%) of 116 women with uterine anomalies. These were the most common malformations and appeared significantly more frequently than the other anomalies (P <0.05). The other anomalies included bicornuate uterus, arcuate uterus and unicomate uterus in 12 (10.3%), 18 (15.5%) and 15 (12.9%) patients, respectively.
The demographic characteristics and pregnancy complications of both study groups are presented in Table 1. Patients with uterine anomalies had significantly lower gravidity than that of the normal uterus group. The mean maternal age in the uterine anomalies group was significantly lower than that of the normal uterus group.
Peripartum outcomes and perinatal outcomes of women with uterine anomalies
Patients with uterine anomalies had significantly higher rates of malpresentation (38.8%), preterm delivery (19.8%) and cesarean section (78.5%) compared with the normal uterus group. The rate of placental abruption was higher in the uterine anomalies group but did not reach statistical significance. Cervical cerclage was performed in eight women, in whom ultrasonographic examination during pregnancy (gestational age range 14-20 weeks) suggested the presence of cervical incompetence. Only one of nine patients with cervical cerclage had a preterm delivery. The majority of patients in the uterine anomalies group were delivered by cesarean section (71% of term and 86% of preterm deliveries). Malpresentation was the indication in 65.8% of the elective cesarean section (25/38) in the uterine anomalies group and 7.4% (20/270) in the normal uterus group (Table 2).
Table 3 presents the perinatal outcomes. Patients in the uterine anomalies group had significantly lower mean birth-weight and a significantly higher incidence of SGA, low and very low birth-weight infant compared with the normal uterus group. Women in the normal uterus group had a significantly higher incidence of large-for-gestational age (LGA) neonates than patients in the uterine anomalies group. Rates of preterm birth (24-28 weeks, 28-32 weeks and 33-37 weeks) were significantly higher in the uterine anomalies group than the normal uterus group. There were no significant differences in the incidence of perinatal mortality and low 1- and 5-minute Apgar scores between the study groups.
Peripartum outcomes and perinatal outcomes of women with different uterine anomalies
There were significant differences between the women with different uterine anomalies (Tables 4-6), as follows: (1) women with uterus didelphys had higher rates of infertility treatment than other uterine anomalies; (2) the rates of abruption and nonreassuring fetal heart rate as indications for primary cesarean section were higher in women with a septateor unicornate uterus compared with other uterine anomalies; (3) the rate of malpresentation was significantly higher in patients with a septate uterus in comparison with patients with a unicornate uterus; and (4) there were no significant differences between the different uterine anomalies in terms of the rate of peripartum complication and neonatal outcomes. The rates of elective cesarean section were highest in patients with a septate uterusand lowest in patients with arcuate uterus. The observed differences were not significant.
Uterine structural anomalies are often asymptomatic and are often discovered during pregnancy or at the time of abortion or during infertility evaluation1. Depending on the method of patient selection, the reported incidence of uterine anomalies ranges from 0.1% to 10%.1,3 In this study, the incidence of diagnosed uterine anomalies was close to 0.45% (116 of 21 961 pregnancies) of the women who delivered at our department during the study period. The most common anomalies were septate uteri, and the incidence was similar to that reported among fertile women.2 However, the incidence of uterus didelphys was 24.2% in the study group, higher than that reported in other studies.2,8 Although our series is one of the largest series published to date, it is not representative of the general population, because uterine anomalies cannot be diagnosed by simple bimanual pelvic examination and might be missed on ultrasonography.3,4 Laparotomy or laparoscopy is more appropriate for distinguishing bicornuate and septate uterus.9 In the current study, all of the uterine anomalies were diagnosed by hysterosal-pingogram (HSG) or during abdominal surgical procedures.
Compared with women with a normal uterus, the women with uterine anomalies had significantly lower gravidity. Furthermore, the mean maternal age was significantly lower in the uterine anomalies group than in the normal uterus group. Similar results have also been reported elsewhere. In the present survey we did not observe any other significant difference in terms of maternal characteristics between the two groups. This finding is in contrast with the finding of other studies that revealed a significantly increased rate of gestational hypertension in women with uterine anomalies, as well as a twofold higher frequency of preeclampsia.10,11
High premature labor, malpresentation and fetal growth retardation (FGR) rates have been reported by many investigators.6-8 Our study supports these findings. Four etiological theories have been suggested to explain the poorer obstetric outcome in patients with uterine anomalies: (1) Abnormal anatomy of the uterine cavity prevents correct rotation of the fetus to cephalic presentation; (2) Abnormal uterine blood flow which caused by an absent or abnormal uterine or ovarian artery might explain FGR; (3) Cervical incompetence; and (4) Diminished muscle mass of the hemi-uterus.12,13
We found cervical incompetence in 6.5% of the patients with uterine anomalies cases. In fact, unicornate uterus has the highest rate of cervical shortening, and the highest rate of spontaneous preterm birth when the cervix is shortened, of all uterine anomalies.14 There might be cases of cervical incompetence without a previous suggestive history or suggestive findings on HSG, as reported by Ambramovici et al15. In our study, cervical cerclage did not prevent premature delivery in uterine anomalies, but it did improve the outcomes in these women. Similar results were obtained in other studies14-16.
The rate of placental abruption was higher in the uterine anomalies group than in the normal uterus group, which was consistent with a previous report.17 Our series showed that the rates of abruption were higher in women with a septate uterus compared with other uterine anomalies, placentation to the septum and poor vascularity have been suggested as possible reasons.
Fetal mal-presentation is the most common indication for cesarean section in women with uterine anomalies; indeed, 38.8% (45/116) of the women in the uterine anomalies study group underwent cesarean section caused as a result of fetal malpresentation. The higher incidence of malpresentation in patients with uterine anomalies has been well documented by other investigators.18,19 Patients in the uterine anomalies group had significantly lower mean birth-weight and a significantly higher incidence of SGA, low and very low birth-weight than those with a normal uterus. Patients with a normal uterus had a significantly higher incidence of large-for- gestational age (LGA) neonates than patients in the uterine anomalies group. Women with uterine anomalies had significantly higher rates of preterm birth (<28 weeks, 28-32 weeks, and 33-37 weeks) than those with a normal uterus. However, aside from the lower birth-weight in the uterine anomalies, we did not observe a significant difference in perinatal outcome among the groups of patients with different uterine anomalies. A previous report20 suggested marked differences in the rate and pattern of pregnancy complications observed in the different types of uterine anomalies. However, we did not find such differences between the specific type anomalies.
In conclusion, our study has provided new insights into the obstetric outcome of utrine malformations. We hope that this study will allow clinicians to better assist patients with known anomalies in negotiating the unique anatomy and physiology of their conditions. Furthermore, clinicians might be able to better counsel women on making decisions regarding their current and future pregnancies.
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