A total of 22775 babies were born between January 2016 and December 2018 in the Shunde Women and Children’s Hospital of Guangdong Medical University. The proportion of infants conceived by embryo transfer was 1.4%. In this study, we found that the proportion of geriatric pregnancies was higher in the ET group than in the NC group, as well as the overall age of pregnant women (33.23 ± 4.59 vs 30.16 ± 5.19 years). Geriatric IVF pregnancy was previously reported as having poorer outcomes than IVF pregnancy in younger women. One study found that among women of childbearing age, those aged 20–30 years had the best IVF outcomes and women aged 40 years and older had poor IVF outcomes and a higher rate of miscarriage [4]. Secondary school includes junior high school and senior high school. China has a nine-year compulsory education system, and all children can go to junior high school for free, so the proportion of women with secondary school education is the highest. As women age, a decline in oocyte production and quality (known as ovarian aging) becomes the primary cause of poorer IVF outcome [5]. We observed that the percentage of women with one pregnancy only was higher in the ET group (48.0%) than in the NC group (31.0%), which was consistent with the findings of Egbe et al. [6] This difference may be attributable to the various causes of infertility in the ET group, meaning women in the ET group were more likely to be having their first pregnancy than those in the NC group. Ectopic pregnancy is the primary cause of early maternal morbidity and mortality, accounting for 1–2% of all pregnancies and ectopic pregnancy incidence has drastically increased with the advancement of ART [7]. The fallopian tube is the most common site of ectopic implantation [8], and about 1.5–2.1% of patients with ectopic pregnancy have undergone IVF [7]. Our findings showed that the percentage of women with a history of ectopic pregnancy was higher in the ET group (15.3%) than in the NC group (2.7%), which may be associated with previous ectopic pregnancy, history of infertility, history of surgery or the use of intrauterine contraceptive device [9].
For gestational comorbidity, the study by Kouhkan et al. [10] showed that women who underwent ET needed more insulin than those in the NC group. Insulin resistance and glucose intolerance during pregnancy can lead to the development of GDM, which explains the higher incidence of GDM in the ET group (42.1%) relative to the NC group (26.4%) in our study.
Preeclampsia is a pregnancy-specific disease with a global prevalence of 5–8%. It is one of the leading causes of maternal and perinatal morbidity and mortality worldwide, causing 50,000 to 60,000 deaths every year [11]. In our study, preeclampsia incidence was higher in the ET group. Preeclampsia is a multisystemic syndrome, and its pathogenesis and pathophysiology involve both genetic and environmental factors [12]. If preeclampsia is not effectively treated in a timely manner, it may endanger the life of the mother and infant or cause sequelae in the short term, and subsequently affect the health of the mother in the long term. Therefore, pregnant women are recommended to complete all prenatal examinations and adhere to a healthy routine and lifestyle. We also found that the incidence of gestational anemia and the number of days of treatment to prevent miscarriage were higher in the ET group (26.0% and 8.45 ± 7.408, respectively) than in the NC group (4.1% and 4.80 ± 4.026, respectively). Most pregnant women who required treatment for miscarriage prevention had threatened labor. The pathogenesis of gestational anemia has been shown to be associated with the age and educational background of pregnant women, as well as a history of ectopic pregnancy [13]. This was consistent with our results, which found that age and incidence of ectopic pregnancy were both higher in the ET group than in the NC group. In addition, ET itself may be a factor associated with gestational anemia. A previous study has demonstrated that severe anemia in pregnant women can lead to premature labor, spontaneous abortion, low birth weight and fetal death [14]. Therefore, implementation of measures to prevent anemia is recommended for women who plan to undergo ET, to ensure maternal and neonatal health.
Analysis of the delivery records revealed that the proportion of women with a high-risk (class III) pregnancy was significantly higher in the ET group (81.3%) than in the NC group (44.9%). Pregnancy risk is primarily classified based on the general conditions of the pregnant woman (age, history of miscarriage, and history of adverse pregnancy), gestational comorbidities (hypertension, anemia, and respiratory infection), and gestational complications (threatened premature labor, GDM, and fetal macrosomia). Age, ART, and twin pregnancy may be the causes for the higher pregnancy risk in the ET group compared with the NC group. The dominant mode of delivery was cesarean section in the ET group (78.2%) and vaginal delivery in the NC group (81.0%). The rate of twin birth was higher in the ET group (39.6%) than in the NC group (1.8%); twin birth is known to be associated with ET. Twin pregnancy imposes certain risks to both maternal and neonatal health, so this issue needs to be carefully considered in the application of ET.
A study by Zhu et al. [15] demonstrated that embryo transfer was associated with higher incidence of premature birth, low birth weight and small-for-gestational age infants. Here, we found that premature birth and low birth weight were observed in 38.8% and 36.5% of women with ET, respectively. The risk of premature birth is higher among women undergoing IVF, but such risk is mostly believed to be a secondary consequence of the significant increase in multiple pregnancies [16]. Our study also showed that the ET group had a higher incidence of twin pregnancy. Furthermore, Qin et al. [17] demonstrated that low birth weight was positively correlated with ART, which was consistent with our findings that the proportions of premature and low birth weight babies were higher in the ET group (24.9% and 18.7%, respectively) than in the NC group (14.1% and 11.2%, respectively) when we compared neonatal clinical outcomes. Compared with the ET group, the NC group had a higher percentage of umbilical cord wrapping around the baby’s neck and foot but a lower percentage of umbilical cord torsion. The umbilical cord is a conduit between the fetus and the placenta that mediates substance exchange between the fetus and mother. Umbilical cord complications are generally considered to be the root cause for chronic intrauterine hypoxia, reduced fetal movement, growth retardation and oligohydramnios [18]. Therefore, regular prenatal examinations are recommended for pregnant women, especially ultrasound examination during the second and third trimesters of pregnancy, to ensure early identification of umbilical cord abnormality.
In summary, the ET group had poorer maternal clinical outcomes than the NC group and higher incidences of premature birth and low birth weight. These differences may be associated with maternal physical fitness, nutritional status, financial status, past health status, ET, and higher rates of reported adverse outcomes due to closer monitoring of pregnant women with ET. Women who plan to have ET are recommended to undergo the procedure at an appropriate reproductive age, maintain physical fitness and good nutrition, and take good prenatal care.