The rate of adolescent pregnancy (aged 10-19 years) was 1.4% in Hebei Province, China from 2013 to 2017, lower than 4.3% from 2010 to 2011 reported by Ganchimeg, T. et al [2]. The difference of the rate may result from the difference of areas, periods and data-collection system. We collected the data of 289,859 pregnant women in Hebei Province for 5 years, which is a developed area in eastern China. Ganchimeg T. et al. [2] collected the data of 314,623 pregnant women from 29 countries for 2 to 4 months, but their sample size from China was smaller than ours. Ganchimeg T. et al. [2] collected the data only from the tertiary hospitals, but our data was collected from all levels of hospitals (including tertiary hospitals, secondary hospitals, primary hospitals). Therefore, our research was representative of the situation of adolescent pregnancy in Hebei Province of China.
Consistent with several previous studies worldwide [1, 2, 13, 14, 24-26], our study showed that, compared with the adult pregnant women (aged 20-34 years), the adolescent pregnant women had significantly lower level of education, less numbers of prenatal care, and higher single-hood rate. Our data showed that there were more adolescent pregnant women that delivered in provincial and municipal hospitals than adult pregnant women, and those adolescent women that delivered at home were 2-3 times more of the adult group. Moreover, the number of unmarried adolescent pregnant women was 10 times higher than that in adults. The reasons for the situation above could be attributed to the factors such as poverty, low education, lack of sex education and contraceptive methods [12, 27]. In addition, adolescent pregnant women lacked economic independence [11], and they might be difficult to deal with the burden of pregnancy [13].
The risk of cesarean delivery in adolescent pregnancy reduced by 25% than adult pregnancy, which was consistent with the previous found, with aRR (95%CI) varying from 0.49 (0.42-0.59) to 0.79 (0.75-0.89) [1, 2, 13, 16, 28, 29]. In fact, adolescent women were at the stage of physical growth, with immature reproductive system, and the incidence of cephalopelvic disproportion in adolescent pregnancy was higher than that of adult women [30]. But why was the rate of cesarean delivery in adolescent pregnancy was lower than that of the adult pregnancy? First, the adolescent women aged 18-19 years accounted for more than half of all adolescent pregnant women, their physical development was basically mature [31]. Second, the pelvic cavity of adolescent women was smaller than that of adult women, and the fetal weight was relatively lower [32]. More preterm delivery and lower fetal weight was conducive for the adolescent women to make vaginal delivery [2, 33]. And for the younger adolescent women (aged 10-17 years), the risk of cesarean delivery even could reduce by 49%, which might be related to their limited access to cesarean delivery [2].
The endocrine-regulating system of adolescent women is not in perfect condition [34], with higher risks of obesity or GDM, but we found a lower risk of GDM in older adolescents (18-19 years) and younger adults (20-24 years) compared with women aged 25-34 years. This result was basically consistent with another study on the delivery population in Beijing, China, with aRR (95%CI) was 0.55 (0.39-0.77) [28]. Marvin-Dowle, K. et al. [29] showed that the risk of GDM in adolescent pregnancy of Pakistani and white British was similar to our results, with aRR (95%CI) value of 0.35 (0.20-0.62), but the risk value was lower, which may be caused by different races. Further studies would be made to investigate the reasons of the lower risk of GDM in adolescents.
We found that the risk of stillbirth and neonatal death in adolescent pregnancy aged 10 to 19 years was 2.58 times and 2.63 times of that in adults pregnant women, in the younger pregnant women aged 10 to 17 years, the risk was higher (stillbirth, aRR: 5.69, 95%CI: 3.36-9.65 and neonatal death,aRR: 7.57, 95%CI: 3.74-15.33). We got the similar results on stillbirth as Ganchimeg, T. et al. [30], with aRR (95%CI) : 1.32 (1.11-1.57) for the younger adolescent pregnant women aged 16 to 17 years, which also was in line on perinatal death as the report of Althabe, F. [25], with aRR (95%CI): 1.13 (1.02-1.25) for the adolescent pregnant women aged 15 to 19 years. Our study confirmed the increased risk of preterm delivery (aRR: 1.76, 95%CI:1.54-2.01) in adolescent than adults. Our study got the corroborated results as many other studies on the risk of preterm delivery in adolescence, with aRR (95%CI) varying from 1.18 (1.11-1.27) to 2.15 (1.26-3.67) [1, 2, 24, 28, 29]. On the contrary, Althabe, F.et al. [25] found that African-American adolescent women had lower preterm delivery rate than adult women, which might be due to ethnic difference. The increased risk of SGA [aRR (95%CI): 1.19 (1.08-1.30)] in adolescent pregnancy in our study was consistent with that of Agbor, V. N. et al. [13], with aRR (95%CI): 1.7(1.1-2.6). Younger adults (20-24 years) had higher risks of preterm delivery, stillbirth, and neonatal death than adult women aged 25-34 years, but lower than adolescent women. Adolescent women were at the stage of development, their uteri were immature, the blood supply to the placenta was affected by the competition between mother and fetus. Preterm delivery and SGA were associated with maternal malnutrition [35], and preterm delivery was positively associated with the risk of perinatal death [36]. Appropriate prenatal care could reduce the incidence of preterm delivery and stillbirth [37]. With less perinatal care and insufficient nutrition during pregnancy, the intrauterine growth and development of the fetus was affected. And the less perinatal care the adolescent pregnant had during their pregnancies, the less preventive intervention on time they would take [38]. We believed that with the maturity of reproductive system, the incidence of adverse outcomes were gradually decreased.
The adverse maternal outcomes of the adolescent pregnant had no difference from those of adult pregnant in our study, such as in PE, placenta previa, placental abruption, postpartum hemorrhage, and some studies were consistent with our findings [13, 16, 25, 26, 29]. Some studies found that adolescent pregnancy increased the risk of postpartum hemorrhage [1, 16]and PE [1]. Other studies found that adolescent pregnancy reduced the risk of postpartum hemorrhage [24] and PE[2]. We think that race, local medical skill level and sample size may be related to these differences. Previous report has found that adolescent pregnancy was a risk factor for increased maternal mortality [39, 40]. We found that maternal mortality in adolescent pregnancy was higher than that of adult women. However, adolescent pregnancy was not a risk factor for maternal mortality after adjusting the confounding factors. The increase in maternal mortality during adolescent pregnancy was related to the social factors such as maternal poverty and education [40], and the lack of medical resources may also affect maternal mortality [41]. After structural equation model analysis, we also found that preterm delivery and cesarean delivery had an indirect effect on the correlation between adolescent pregnancy and neonatal death. The total effect of adolescent pregnancy on neonatal death increased via the indirect effects of preterm and cesarean delivery.
We used the government-funded HBMNMSS as our data source, the data covered 10 cities, with large sample size and representative population. The data was collected not only from tertiary hospitals, but also from secondary and primary hospitals, which could truly reflect the situation of adolescent pregnancy in Hebei Province. But there were some limitations in our research, vast majority of adolescent pregnant women were 18-19 years old, the conclusion was mainly based on the older adolescent pregnant women. The database did not contain the information about smoking and maternal BMI and economic status. These confounding factors might affect the adverse pregnancy outcomes. The diagnosis system was not widely used in Hebei Province, which might lead to some bias in our study.