Objective: To investigate the impact of preconception body mass index (BMI) on neonatal birth weight and the risk of macrosomia in pregnant women across various age groups. Methods: A cohort study was conducted, selecting pregnant women who underwent their initial prenatal assessment at Beijing Obstetrics and Gynecology Hospital from September 1st, 2018 to March 31st, 2020. Relevant data were collected from the hospital's electronic medical record system. Logistic regression nested cubic spline was used to analyze the nonlinear association between preconception BMI and neonatal birth weight. Binary logistic regression was also employed to assess the association between preconception BMI and macrosomia risk. Results: (1) A total of 13 015 pregnant women were examined, revealing an incidence of macrosomia of 6.33% (824/13 015). The preconception BMI of pregnant women in the macrosomia group was significantly higher than that in the non-macrosomia group [(23.1±3.4) vs (21.6±3.1) kg/m2], and the age was significantly higher than that in the non-macrosomia group [(32.1±3.6) vs (31.7±3.7) years], the differences were statistically significant (all P<0.05). (2) Preconception BMI was positively correlated with neonatal birth weight. Pregnant women with preconception BMI of 15.0 kg/m2, 20.0 kg/m2, and 25.0 kg/m2 had decreased birth weight of 121 g (95%CI: 35-183 g) and increased birth weights of 78 g (95%CI: 54-102 g) and 182 g (95%CI: 151-213 g), respectively, compared to those with a preconception BMI of 18.0 kg/m2. (3) For each 1.0 kg/m2 increase in preconception BMI, the risk of macrosomia increased by 14% (OR=1.14, 95%CI: 1.11-1.16; P<0.001). When stratified by age, it was observed that elevated preconception BMI significantly increased the incidence of macrosomia in women aged 27-38 years. Among them, the risk of delivering macrosomia among 37 years old pregnant women was most affected by preconception BMI (OR=1.33, 95%CI: 1.17-1.51; P<0.001). (4) The stability and sensitivity analysis results showed that the preconception BMI of pregnant women with a preconception BMI of 18.0-<25.0 kg/m2 had a significant impact on the risk of macrosomia (OR=1.23, 95%CI: 1.17-1.29; P<0.001), while the preconception BMI of other preconception BMI stratification pregnant women had no significant impact on the risk of macrosomia (all P>0.05). Hypertension disorders in pregnancy, gestational diabetes mellitus and abnormal blood lipid during pregnancy were not the mediators associated with preconception BMI and macrosomia. After excluding three factors respectively, the impact of preconception BMI on the risk of macrosomia was the same as before (OR=1.14, 95%CI: 1.11-1.16; P<0.001). Conclusions: Preconception BMI is linked to neonatal birth weight and the risk of macrosomia, which is influenced by the pregnant woman's age. Both factors should be considered when evaluating the risk of macrosomia in clinical practice.
目的： 探讨不同年龄孕妇孕前体重指数（BMI）对新生儿出生体重及分娩巨大儿风险的影响。 方法： 应用队列研究方法，选取2018年9月1日至2020年3月31日在首都医科大学附属北京妇产医院进行首次产前检查并在本院分娩的孕妇，通过医院电子病历系统获取临床信息，依据新生儿出生体重分为非巨大儿组（12 191例）和巨大儿组（824例），比较两组的一般临床资料；采用logistic回归嵌套立方样条函数分析孕前BMI与新生儿出生体重的非线性相关关系，采用二元logistic回归，按年龄分层，逐层分析孕前BMI与分娩巨大儿风险的关联。 结果： （1）本研究共纳入13 015例孕妇，巨大儿分娩率为6.33%（824/13 015）。巨大儿组孕妇的孕前BMI显著高于非巨大儿组［分别为（23.1±3.4）、（21.6±3.1）kg/m2］，年龄大于非巨大儿组［分别为（32.1±3.6）、（31.7±3.7）岁］，分别比较，差异均有统计学意义（P均<0.05）。（2）孕前BMI与新生儿出生体重总体上呈正相关。与孕前BMI为18.0 kg/m2的孕妇相比，孕前BMI为15.0 kg/m2孕妇的新生儿出生体重降低了121 g（95%CI为35~183 g），孕前BMI为20.0 kg/m2、25.0 kg/m2孕妇的新生儿出生体重分别增加了78 g（95%CI为54~102 g）和182 g（95%CI为151~213 g）。（3）孕前BMI每增加1.0 kg/m2，分娩巨大儿的风险增加14%（OR=1.14，95%CI为1.11~1.16；P<0.001）。按年龄分层分析显示，27~38岁的孕妇孕前BMI升高均显著增加巨大儿的分娩率，其中，37岁孕妇分娩巨大儿的风险受孕前BMI影响最大（OR=1.33，95%CI为1.17~1.51；P<0.001）。（4）稳定性及敏感性分析结果显示，孕前BMI为18.0~<25.0 kg/m2孕妇的孕前BMI对分娩巨大儿的风险有显著影响（OR=1.23，95%CI为1.17~1.29；P<0.001），其他孕前BMI分层孕妇的孕前BMI对分娩巨大儿的风险均无显著影响（P均>0.05）。妊娠期高血压疾病、妊娠期糖尿病及妊娠期血脂异常均不是孕前BMI与巨大儿关联的中介因素，分别排除3种因素后，孕前BMI对分娩巨大儿风险的影响与未排除中介因素前均一致（OR=1.14，95%CI为1.11~1.16；P<0.001）。 结论： 孕前BMI与新生儿出生体重呈正相关，孕前BMI升高增加分娩巨大儿的风险，但因孕妇年龄而异。临床实践中评估分娩巨大儿风险时应同时关注孕妇年龄和孕前BMI。.