Association between pregnancy-related factors and stillbirth: a retrospective cohort study based on 500 000 pregnant residents in Wuhan / 中华围产医学杂志

ABSTRACT

Objective:To analyze the incidence of stillbirth and the associated factors in pregnancy among pregnant residents in Wuhan.Methods:A previous birth cohort was retrospectively reviewed. The cohort was based on Wuhan Maternal and Child Information System, and the perinatal information of pregnant residents in Wuhan from January 1, 2011, to September 30, 2017 and information of selected cases was collected, including socio-demographic characteristics, pregnant history, and healthcare information during pregnancy and labor. Data on stillbirth, including fetal death in uterus and in labor, were selected for this study. Chi-square test was adopted for comparing the differences in pregnancy-related factors between live birth and stillbirth, and binary logistic regressions for exploring the influencing factors associated with the occurrence of stillbirth. Results:A total of 509 057 deliveries in Wuhan were included in this study, including 505 839 live births and 3 218 stillbirths (3 155 after exclusion of fetal death in labor), with an overall incidence of stillbirth of 6.32‰(3 218/509 057), and an annual incidence between 4.90‰ to 8.11‰. Statistically significant differences were found between the live birth and stillbirth group in the following items maternal age [<25 years old 19.28% (97 544/505 839) vs 19.36% (623/3 218); 25-30 years old 48.45% (245 077/505 839) vs 45.15% (1 453/3 218); 30-35 years old 26.09% (131 952/505 839) vs 26.29% (846/3 218); >35 years old 6.18% (31 266/505 839) vs 9.20% (296/3 218)], educational background [middle school or below 22.90% (115 833/505 839) vs 22.03% (709/3 218); high school 36.37% (183 978/505 839) vs 38.72% (1 246/3 218); college or above 40.73% (206 028/505 839) vs 39.25% (1 263/3 218)], occupation [brainworker or professionals 33.51% (169 514/505 839) vs 31.54% (1 015/3 218); manual or freelance worker 66.38% (335 763/505 839) vs 68.34% (2 199/3 218)], residential area [urban area 70.00% (354 365/505 839) vs 76.32% (2 456/3 218); rural area 30.00% (151 474/505 839) vs 23.68%(762/3 218)], and time of conception [spring (March to May) 24.27% (122 746/505 839) vs 24.08% (775/3 218); summer (June to August) 24.09% (121 867/505 839) vs 23.87% (768/3 218); fall (September to November) 26.69% (135 012/505 839) vs 25.08% (807/3 218); winter (December to next February) 24.95% (126 214/505 839) vs 26.97% (868/3 218)] (all P<0.05), but no significant difference was found in fetal gender ( P>0.05). Besides, gravidity [once 49.32% (249 484/505 839) vs 47.02% (1 513/3 218); over twice 50.68% (256 355/505 839) vs 52.98% (1 705/3 218)], parity [once 73.60% (372 316/505 839) vs 77.07% (2 480/3 218); over twice 26.40% (133 523/505 839) vs 22.93% (738/3 218)], history of stillbirth [0.33% (842/256 355) vs 0.65% (11/1 705)], hypertensive disorders in pregnancy [3.25% (16 464/505 839) vs 5.59% (180/3 218)], first trimester vaginal bleeding [2.02% (10 251/505 839) vs 2.61% (84/3 218)], placenta previa [0.98% (4 963/505 491) vs 2.64% (53/2 009)], and oligohydramnios [2.52% (12 764/505 839) vs 1.90% (61/3 218)] differed significantly between the two groups (all P<0.05). However, no significant difference was found between the two groups in terms of the proportion of women with gestational diabetes mellitus and previous spontaneous abortion (both P>0.05). After exclusion of fetal death in labor from the 3 218 stillbirths, the same results were achieved. Binary logistic regression analysis showed that women who were over 30 years old (30-35 years old OR=1.42, 95% CI 1.30-1.56; >35 years old OR=2.59, 95% CI 2.25-2.98), with a high school degree or below (middle school or below OR=1.37, 95% CI 1.21-1.55; high school OR=1.28, 95% CI 1.16-1.42), manual or freelance worker ( OR=1.18, 95% CI 1.07-1.31), in the urban area ( OR=1.43, 95% CI1.31-1.57), and gravidity ≥ 2 times ( OR=1.32, 95% CI 1.21-1.43), primiparity ( OR=1.76, 95% CI 1.58-1.96), gestational hypertension ( OR=2.80, 95% CI 2.40-3.27), vaginal bleeding in the first trimester ( OR=1.35, 95% CI 1.08-1.68), placenta previa ( OR=10.86, 95% CI 8.84-13.35) and history of stillbirth ( OR=2.27, 95% CI 1.30-3.98) were all risk factors of stillbirth. Conclusion:Pregnant women who were over 30 years old, less educated, manual worker or freelance or with a history of adverse pregnancy, vaginal bleeding in the first trimester, hypertension in pregnancy, and placenta previa are at higher risk of stillbirth