To explore the characteristics of neonatal birth weight (BW) in two consecutive term singleton pregnant women and to investigate the influencing factors of macrosomia in the second birth.

In this case-control study, medical records of 1 920 singleton full-term pregnant women who gave birth twice in Peking University First Hospital from January 2005 to December 2017 were reviewed. All subjects were divided into two groups according to neonatal BW at the second birth regardless of the first one: macrosomia group (n=122) and non-macrosomia group (n=1 798). Then, those two groups were further divided into four sub-groups based on the neonatal BW in the first birth: macrosomia at both deliveries (n=27), macrosomia at the second time and non-macrosomia at the first time (n=95), non-macrosomia at the second time and macrosomia at the first time (n=90) and non-macrosomia at both deliveries (n=1 708). The differences of delivery interval, and the maternal age, pre-pregnancy body mass index (BMI), weight gain during pregnancy, area under the curve of oral glucose tolerance test results, weight retention, the incidence of diabetes in pregnancy (including gestational diabetes mellitus and diabetes mellitus complicated with pregnancy), incidence of hypertensive disorders during pregnancy and cesarean section rate at the second pregnancy between the groups and sub-groups were compared with t-test, Chi-square test and logistic regression analysis.

(1) The total average neonatal BW in the second pregnancy was higher than that in the first [(3 443±378) vs (3 403±396) g, t=-4.119, P<0.001]. However, the proportion of macrosomia in each group was similar [6.4% (122/1 920) vs 6.1% (117/1 920), χ²=3.237, P=0.198]. The pre-pregnancy BMI, weight gain during pregnancy and proportion of previous macrosomia in the macrosomia group were significantly higher than those in non-macrosomia group [(23.6±3.4) vs (22.7±3.1) kg/m², t=-2.882, P=0.004; (13.4±5.0) vs (12.4±4.1) kg, t=-2.522, P=0.037; 22.1% (27/122) vs 5.0% (90/1 798), χ²=58.554, P<0.001]. Logistic regression analysis showed that previous macrosomia (OR=4.979, 95%CI: 3.052-8.122, P<0.001), pre-pregnancy BMI (OR=1.084, 95%CI: 1.023-1.149, P=0.001) and weight gain during pregnancy (OR=1.077, 95%CI: 1.031-1.125, P=0.007) were influencing factors for macrosomia in the index delivery. (2) The pre-pregnancy BMI in the subgroup of macrosomia at both deliveries was significantly higher comparing to the subgroup of non-macrosomia at the second time and macrosomia at the first time [(25.8±4.3) vs (23.9±2.9) kg/m², t=2.600, P=0.011]. Women in the subgroup of macrosomia at the second time and non-macrosomia at the first time had higher weight gain during second pregnancy than the subgroup of non-macrosomia at both deliveries [(13.5±4.2) vs (12.5±4.1) kg, t=-2.404, P=0.016].

For two consecutive term singleton pregnancies, the average neonatal BW in the second time is slightly higher than that in the first, but the incidence of macrosomia is similar. Pre-pregnancy BMI, weight gain during pregnancy and macrosomia in the first birth are influencing factors for macrosomia in the second pregnancy. More attention should be paid to pre-pregnancy BMI reduction in women with history of macrosomia. For women without a history of macrosomia, weight management should be emphasized during the second pregnancy.

Birth weight; Fetal macrosomia; Body mass index; Infant, newborn; Pregnancy; Weight gain