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Objectives : This study aimed to establish normal blood pressure reference ranges across gestation and maternal characteristics. Methods : We conducted a follow-up study including 29,200 Chinese normal pregnant women. Multilevel restrictive cubic spline models were used to calculate normal blood pressure reference ranges among all population and stratified groups. Results : In all normal pregnancies, the normal reference range of systolic blood pressure were 93.94-118.74 mmHg(2.5 th -97.5 th ) and 97.35-124.63 mmHg at 12 and 37 weeks gestation, respectively while 58.79-74.21 mmHg and 59.19-78.25 mmHg were for diastolic blood pressure at 12 and 37 weeks gestation, which differed in subgroups stratified by prepregnancy body mass index and maternal age. Conclusion : This study provides evidence for blood pressure management in Chinese pregnant women.

The influences of blood pressure in early to mid-pregnancy on the risk of small-for-gestational-age (SGA) birth are not clear. Our objective was to examine the associations of the blood pressure levels at 10 and 18 gestational weeks with the risk of SGA birth. Data were obtained from the Chinese Maternal and Newborn's Health Monitoring System (MNHMS). In total, 50745 Chinese women who delivered a single live infant at a gestational age of between 28 and 42 weeks were included in this analysis. Blood pressure, birth outcome and other related information were obtained during antenatal visits by obstetricians. Logistic regression models were used to examine the associations, adjusting for potential confounders. The total incidence of SGA birth was 8.9%. High blood pressure levels at 10 gestational weeks significantly increased the risk of SGA birth (SBP: RR = 1.32, 95% CI: 1.11-1.56; DBP: RR = 1.10, 95% CI: 1.05-1.14). The incidence of SGA birth was not associated with the DBP at 18 gestational weeks but showed a U-shaped relationship with SBP. A decrease in blood pressure from 10 to 18 gestational weeks was associated with an increased risk of SGA birth (SBP: RR = 1.03, 95% CI: 1.00-1.07; DBP: RR = 1.05, 95% CI: 1.02-1.09). Our results provide evidence on the relationship of blood pressure in early and mid-pregnancy with SGA birth. Higher blood pressures during early pregnancy and greater decreases in blood pressure from early to mid-pregnancy increased the risk of SGA birth, indicating a continuum of risk for SGA birth based on blood pressure starting during early pregnancy.