Preeclampsia Prevalence, Risk Factors, and Pregnancy Outcomes in Sweden and China

IMPORTANCE: Preeclampsia is a leading cause of maternal and perinatal morbidity and mortality worldwide. Within-country studies have reported racial differences in the presentation and outcome, but little is known about differences between countries. OBJECTIVE: To compare preeclampsia prevalence, risk factors, and pregnancy outcomes between the Swedish and Chinese populations. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study compared deliveries from the Swedish national Medical Birth Register (2007-2012) and the China Labor and Delivery Survey (2015-2016). The Swedish Medical Birth Register records maternal, pregnancy, and neonatal information for nearly all deliveries in Sweden. The China Labor and Delivery Survey was conducted throughout China, and these data were reweighted to enable national comparisons. Participants included 555 446 deliveries from Sweden and 79 243 deliveries from China. Data management and analysis was conducted from November 2018 to August 2020 and revised in February to March 2021. EXPOSURES: Maternal characteristics, parity, multiple gestation, chronic and gestational diabetes, cesarean delivery. MAIN OUTCOMES AND MEASURES: Preeclampsia prevalence and risk factors, overall and for mild and severe forms and rates of adverse neonatal outcomes compared with pregnancies with no gestational hypertension. RESULTS: The 555 446 Swedish pregnancies and 79 243 Chinese pregnancies had mean (SD) maternal age of 30.9 (5.3) years and 28.6 (4.6) years, respectively. The overall prevalence of preeclampsia was similar in Sweden and China, 16 068 (2.9%) and 1803 (2.3%), respectively, but with 5222 cases (32.5%) considered severe in Sweden and 1228 cases (68.1%) considered severe in China. Obesity (defined as BMI ≥28 in China and BMI ≥30 in Sweden) was a stronger risk factor in China compared with Sweden (China: odds ratio [OR], 5.12; 95% CI, 3.82-6.86; Sweden: OR, 3.49; 95% CI, 3.31-3.67). Nulliparity had a much stronger association with severe preeclampsia in Sweden compared with China (Sweden: OR, 3.91; 95% CI, 3.65-4.18; China: OR, 1.65; 95% CI, 1.20-2.25). The overall stillbirth rate for singleton in China was more than 3-fold higher than in Sweden (846/77 512[1.1%] vs 1753/547 219 [0.3%], P < .001), and 10-fold higher among women with preeclampsia (66/1652 [4.6%] vs 60/14 499[0.4%], P < .001). CONCLUSIONS AND RELEVANCE: In this study, the prevalence rates of preeclampsia in Sweden and China were similar, but women in China had more severe disease and worse pregnancy outcomes than women in Sweden. The associations of obesity and nulliparity with preeclampsia suggest a role for lifestyle and health care factors but may reflect some differences in pathophysiology. These findings have relevance for current efforts to identify high-risk pregnancies and early serum markers because the value of risk prediction models and biomarkers may be population specific.