Prevalence, risk factors, and adverse maternal and fetal outcomes of anemia during pregnancy: a retrospective study in China, 2012-2020.

backgroundAnemia is a public world health problem among pregnant females especially in developing countries. China is a representatively developing country with vast territory and significant economic and cultural differences in different regions. Currently most studies on anemia in pregnancy ignored economically backward and resource-poor cities or districts and anemia during pregnancy in China was not accurately estimated. The goal of this study was to assess the prevalence, risk factors, and adverse outcomes of anemia among pregnant females across different regions of China using a large, nationally representative dataset from 2012 to 2020.

methodA large representative multicenter retrospective study collected data from the National Maternal Near Miss Surveillance System (NMNMSS). The study covered 30 provinces (Tibet excluded), eastern, central, and western regions, both rural and urban areas, as well as medical institutions at all levels. A total of 438 medical institutions participated, with 12, 572, 647 singleton pregnant women and 237, 864 multiple pregnant women enrolled. Socio-demographic characteristics, hemoglobin levels, risk factors and pregnancy outcomes were collected via the online NMNMSS platform from all the participants and the study showed the current real situation of anemia during pregnancy in China during 2012-2020.

resultsA total of 12,810,511 pregnant females aged 15 to 49 years were included. The overall prevalence of pregnancy-associated anemia was 21.25%, with 8.44% mild anemia, 12.03% moderate, 0.58% severe, and 0.20% of unknown severity. The anemia prevalence was 21.08% among singleton pregnancies (1,063,104 mild, 1,492,873 moderate, 69,402 severe, 24,922 unknown severity) and 30.31% among multiple pregnancies (18,156 mild, 48,686 moderate, 4,710 severe, 24,922 unknown severity). Notably, moderate anemia accounted for the largest proportion of anemic cases across all pregnancies. Compared with the singleton pregnancy group, the multiple pregnancy group had significantly higher risks of moderate and severe anemia, which were 1.7-fold and 10-fold higher, respectively. Additionally, gestational anemia was significantly associated with maternal age 15-19 years, parity, previous caesarean sections, education status and most maternal complications during pregnancy. Moderate and severe anemia exhibited a significant proportional association with maternal outcomes, including uterine rupture, placenta previa, placental abruption, postpartum hemorrhage, severe postpartum hemorrhage, blood transfusion, intensive care unit (ICU) admission and multiple organ dysfunction syndrome (MODS), and these conditions were further linked to an elevated risk of low birth weight, poor Apgar scores at birth, and stillbirth. No significant elevation in adverse outcome risk was observed in instances of mild anemia.

conclusionBased on large-sample nationwide data of 12.8 million pregnant women in China, this study identified a substantial anemia burden (prevalence: 21.25%), with moderate/severe anemia (12.61%) significantly associated with elevated clinical risks. Multiple pregnancy, as a major risk factor for pregnancy-associated anemia, was associated with a higher anemia prevalence (30.31%) and significantly increased risks of moderate and severe anemia compared with singleton pregnancy (21.08%), with aOR = 1.64 (95% CI: 1.52-1.76). Other risk factors included adolescent pregnancy (15-19 years), low education and obstetric complications. Notably, moderate/severe anemia was associated with heightened maternal and neonatal adverse outcomes, whereas mild anemia exhibited no such associations of risk-stratified screening and preventive strategies to reduce the morbidity and adverse outcomes potentially associated with pregnancy-associated anemmia.