Incidence and factors on anaemia during pregnancy in China: a multicentre prospective cohort study

BACKGROUND: As anaemia during pregnancy is common in China, we sought to investigate the incidence and influencing factors on maternal anemia in the northern part of China.

METHODS: We conducted a prospective cohort study from October 2020 to June 2024 at 13 hospitals in China, enrolling 18 416 pregnant women aged ≥18 years who had regular prenatal examinations, Their data (location, history of anaemia, and haemoglobin (Hb) test results) were collected via an app data collection platform. They were enrolled after providing informed consent in the first trimester at 11-13 weeks, and followed up at 24-27 gestational weeks, 32-35 gestational weeks, and ≥36 weeks. They provided information independently and uploaded their laboratory test results in the form of photographs at each follow up. Univariate and multivariate logistic regression models were used to analysis.

RESULTS: After excluding 7431 participants with incomplete Hb data, we were left with 10 985 pregnatn women who had taken four Hb tests in each interview at 11 hospitals in five provinces. The overall prevalence of maternal anaemia was 23.2% (95% CI = 22.5-24.0%). Its overall incidence in the second or third trimester was 20.5% (95% CI = 19.8-21.3%) and was highest at 24-27 weeks (13.8%, 95% CI = 13.1-14.4%). Factors influencing incident maternal anaemia were parity ≥2 times (OR = 2.1; 95% CI = 1.51-2.92), a history of anaemia before pregnancy (OR = 1.77, 95% CI = 1.41-2.23), and a history of anaemia during a previous pregnancy (OR = 1.71, 95% CI = 1.37-2.13). We observed a positive association between pre-pregnancy BMI categorised as overweight (BMI = 24-27.9: OR = 0.68; 95% CI = 0.59-0.77) or obesity (BMI ≥28: OR = 0.79; 95% CI = 0.67-0.94) with maternal anaemia.

CONCLUSIONS: Both of prevalence and incidence of anaemia in pregnancy were higher in the second trimester. Targeted action is needed for women with a history of anaemia before or during a previous pregnancy and women who had multiple deliveries. Such efforts could include strengthened screening programs or better health education on prenatal nutrition during pregnancy and pre-pregnancy.

REGISTRATION: ClinicalTrials.gov: NCT04486456.