研究目的

探究孕妇孕前BMI、孕期增重对不良母婴结局的影响，为孕妇孕前及孕期体重的管理提供参考依据。

研究方法

采用前瞻性队列研究方法，选择了15个省（自治区、直辖市）的24家医院作为调研现场，于2017年7月25日至2018年11月26日期间，招募孕早期首次前往各医院进行产检的妇女作为研究对象，通过问卷调查和医院信息采集系统收集孕妇的人口学特征、孕前、孕晚及分娩体重、母婴结局等相关信息，采用Logistic回归分析模型和限制性立方样条模型探究孕前BMI及孕期增重与不良母婴结局之间的关联。

研究结果

1.本研究共纳入5031例孕妇作为研究对象。孕前低体重、超重、肥胖的孕妇分别为13.8%、18.2%及3.9%。按照中国营养学会（CNS）推荐的孕期增重标准分类，孕期增重不足、孕期增重过多的孕妇分别为8.6%和52.0%。按照美国医学研究所（IOM）推荐的孕期增重标准分类，孕期增重低于IOM推荐值、孕期增重高于IOM推荐值的孕妇分别为21.9%和40.4%。全部研究对象中，早产率为4.7%；SGA和LGA的发生率分别为6.0%和10.2%；剖宫产率为44.7%；GDM的发病率为14.8%。

2.Logistic回归模型显示，调整相关混杂因素后，孕期增重不足（OR:1.97，95%CI:1.35~2.87）、孕期增重低于IOM推荐值（OR:2.29，95%CI:1.67~3.17）是早产的危险因素，而孕期增重过多（OR:0.61，95%CI:0.46~0.83）的孕妇早产发生风险降低; 孕前低体重（OR: 1.38，95%CI: 1.027~1.854）、孕期增重不足（OR:1.85，95%CI:1.32~2.61）、孕期增重低于IOM推荐值（OR:2.04，95%CI:1.55~2.67）是SGA的危险因素，孕前超重（OR: 0.47，95%CI:0.31~0.71）、孕期增重过多（OR: 0.64，95%CI:0.49~0.83）的孕妇SGA的发生风险降低；孕前超重（OR:1.61，95%CI: 1.29~2.00）、肥胖（OR:1.79，95%CI:1.20~2.67）、孕期增重过多（OR:1.95，95%CI: 1.58~2.41）、孕期增重高于IOM推荐值（OR:2.14，95%CI:1.73~2.66）是LGA的危险因素；孕前超重（OR:1.39，95%CI:1.19~1.62）、肥胖（OR:1.70，95%CI: 1.25~2.31）孕期增重过多（OR:1.42，95%CI:1.25~0.61）、孕期增重高于IOM推荐值（OR:1.35，95%CI:1.18~1.54）是剖宫产的危险因素，孕前低体重（OR:0.84，95%CI:0.70~0.99）、孕期增重低于IOM推荐值（OR:0.82，95%CI:0.70~0.96）的孕妇剖宫产的发生风险降低；孕前超重（OR:1.52，95%CI:1.25~1.84）、肥胖（OR:2.20，95%CI:1.55~3.12）、孕期增重不足（OR:1.57，95%CI:1.25~1.99）是GDM的危险因素，孕前低体重（OR:0.70，95%CI:0.53~0.91）的孕妇GDM的发生风险降低。

3.孕前BMI及孕期增重的联合作用分析发现，与孕前BMI正常且孕期增重适宜的孕妇相比，孕前低体重且孕期增重不足（OR:2.20，95%CI:1.12~4.34）、孕前体重正常且孕期增重不足（OR:1.83，95%CI:1.13~2.97）是早产的危险因素，孕前体重正常且孕期增重过多（OR:0.45，95%CI: 0.31~0.66）的孕妇早产的发生风险降低；孕前低体重且孕期增重不足（OR:2.94，95%CI:1.71~5.04）是SGA危险因素，孕前体重正常且孕期增重过多（OR:0.63，95%CI:0.46~0.85）、孕前超重/肥胖且孕期增重适宜（OR:0.31，95%CI:0.14~0.67）、孕前超重/肥胖且孕期增重过多（OR:0.35，95%CI: 0.21~0.59）的孕妇SGA发生风险降低；孕前体重正常且孕期增重过多（OR:2.20，95%CI:1.68~2.88）、孕前超重/肥胖且孕期增重过多    （OR:3.27，95%CI:2.43~4.40）、孕前超重/肥胖且孕期增重适宜（OR:2.06，95%CI: 1.38~3.08）的孕妇分娩LGA的风险较高；孕前体重正常且孕期增重过多（OR:1.48，95%CI: 1.27~1.72）、孕前超重/肥胖且孕期增重过多（OR:2.04，95%CI: 1.68~2.47）、孕前超重/肥胖且孕期增重适宜（OR:1.65，95%CI:1.27~2.15）的孕妇发生剖宫产的风险增加；孕前超重/肥胖且孕期增重适宜（OR: 1.94，95%CI: 1.44~2.62）、孕前超重/肥胖且孕期增重不足（OR:2.71，95%CI:1.76~4.18）是GDM发病的危险因素。

4.限制性立方样条模型分析结果显示，孕前BMI、孕期增重与不良母婴结局存在剂量反应关系。早产的发生风险随着孕期增重的增加逐渐降低，但未见高孕期增重与早产之间有统计学关联；随着孕前BMI、孕期增重的增加，SGA的发生风险逐渐降低，LGA、剖宫产的发生风险逐渐增加；随着孕前BMI的增加，GDM的发生风险逐渐增加，孕期增重不足时GDM的发生风险较高，但未见高孕期增重与GDM之间有统计学关联。

研究结论

孕前BMI及孕期增重与不良母婴结局间存在统计学关联，不合理的孕前BMI及孕期增重会增加不良母婴结局的发生风险；孕前BMI、孕期增重与不良母婴结局之间存在剂量反应关系，且孕前BMI与孕期增重存在联合作用，因此，在孕期增重时要结合孕前BMI，以避免不合理的孕期增重造成不良母婴结局的发生。

Objective

To explore the effects of pre-pregnancy BMI and gestational weight gain on adverse maternal and infant outcomes, and to provide reference for weight management before and during pregnancy.

Methods

A prospective cohort study was conducted in 24 hospitals in 15 provinces (autonomous regions and municipalities directly under the central government).  From July 25, 2017, to November 26, 2018, women who went to hospitals for obstetric examinations for the first time in the first trimester of pregnancy were recruited as research subjects, and the demographic characteristics of pregnant women, pre-pregnancy, late pregnancy and birth weight, maternal and infant outcomes and other related information were collected through questionnaire surveys and hospital information collection systems. We used logistic regression models and restrictive cubic spline models to analyze the association between pre-pregnancy BMI, gestational weight gain and adverse maternal and infant outcomes.

Results

5031 pregnant women were included in this study. The prevalence of pregnant women with underweight, overweight and obesity before pregnancy was 13.8%, 18.2% and 3.9%, respectively. According to the classification of gestational weight gain recommended by the Chinese Nutrition Society (CNS), 8.6% and 52.0% of pregnant women with insufficient gestational weight gain and excessive gestational weight gain. According to the standard classification of Gestational Weight Gain recommended by the American Medical Research (IOM), 21.9% and 40.4% of pregnant women with gestational weight gain less than the recommended value of IOM and higher than the recommended value of IOM. Among all participants, the incidence of preterm birth was 4.7%, the incidence of SGA and LGA was 6.0% and 10.2%, the caesarean section rate was 44.7%, and the incidence of GDM was 14.8%.

Logistic regression models showed that insufficient gestational weight gain (OR: 1.97, 95% CI:1.35~2.87) and gestational weight gain less than the recommended value of IOM (OR:2.29,95%CI:1.67~3.17) were risk factors for preterm birth, while the risk of preterm birth was decreased in pregnant women with excessive gestational weight gain (OR:0.61,95%CI:0.46~0.83); Pre-pregnancy underweight (OR:1.38, 95%CI: 1.027~1.854), insufficient weight gain (OR:1.85,95%CI:1.32~2.61), gestational weight gain less than IOM recommended (OR:2.04,95%CI:1.55~2.67) were risk factors for SGA, and pregnant women with pre-pregnancy overweight (OR:0.47,95%CI: 0.31~0.71) and excessive gestational weight gain (OR:0.64,95%CI:0.49~0.83) had lower risk of SGA; Pre-pregnancy overweight (OR:1.61, 95%CI:1.29~2.00), obesity (OR:1.79, 95%CI:1.20~2.67), excessive gestational weight gain (OR:1.95, 95%CI: 1.58~2.41), gestational weight gain above the recommended value of IOM (OR: 2.14,95%CI:1.73~2.66) were risk factors for LGA; Pre-pregnancy overweight (OR:1.39,95%CI:1.19~1.62), obesity (OR:1.70,95%CI:1.25~2.31), excessive gestational weight gain (OR:1.42,95%CI:1.25~ 0.61), gestational weight gain higher than the IOM recommendation (OR:1.35, 95%CI:1.18~1.54) were risk factors for caesarean section, while pregnant women with pre-pregnancy underweight (OR: 0.84,95%CI:0.70~0.99) and gestational weight gain less than IOM recommended value (OR:0.82,95%CI:0.70~0.96) had lower risk of caesarean section ; Pre-pregnancy overweight (OR:1.52,95%CI:1.25~1.84), obesity (OR:2.20, 95%CI:1.55~3.12), and insufficient gestational weight gain (OR:1.57, 95%CI:1.25~1.99) were risk factors for GDM, while pregnant women with pre-pregnancy under weight (OR:0.70, 95%CI: 0.53~0.91) had lower risk of GDM.

The combined effect analysis of pre-pregnancy BMI and gestational weight gain found that compared with pregnant women with normal pre-pregnancy BMI and appropriate gestational weight gain, pre-pregnancy underweight weight and insufficient gestational weight gain (OR:2.20, 95%CI:1.12~4.34), normal pre- pregnancy weight and insufficient gestational weight gain (OR:1.83,95%CI:1.13~2.97) were risk factors for preterm birth, and pregnant women with normal pre-pregnancy weight and excessive gestational weight gain (OR: 0.45,95%CI: 0.31~ 0.66) had lower risk of preterm birth; pre-pregnancy underweight and insufficient gestational weight gain (OR:2.94,95%CI:1.71~5.04) was risk factors for SGA, normal pre-pregnancy weight and excessive gestational weight gain (OR:0.63, 95%CI:0.46~0.85), pre-pregnancy overweight/obesity and appropriate gestational weight gain (OR:0.31, 95%CI:0.14~0.67), pre-pregnancy overweight/obesity and excessive gestational weight gain (OR:0.35, 95%CI:0.21~0.59) were protective factors for SGA; pregnant women with normal pre-pregnancy weight and excessive gestational weight gain (OR:2.20,95%CI:1.68~2.88), pre-pregnancy overweight / obesity and excessive gestational weight gain (OR:3.27,95%CI:2.43~4.40), pre-pregnancy overweight/ obesity and appropriate gestational weight gain(OR:2.06, 95%CI:1.38~3.08) was at higher risk of LGA. The risk of caesarean section increases in pregnant women with normal pre-pregnancy weight and excessive gestational weight gain (OR:1.48, 95%CI:1.27~1.72) pre-pregnancy overweight/ obesity and excessive gestational weight gain (OR:2.04, 95%CI:1.68~2.47), pre- pregnancy overweight/obesity and appropriate gestational weight gain(OR:1.65, 95%CI:1.27~2.15); Pre-pregnancy overweight/obesity and appropriate gestational weight gain (OR:1.94, 95%CI: 1.44~ 2.62), pre-pregnancy overweight/obesity and insufficient gestational weight gain (OR: 2.71, 95%CI:1.76~4.18) were risk factors for the development of GDM.

Restrictive cubic spline models showed a dose-response relationship between pre-pregnancy BMI, gestational weight gain and adverse pregnancy outcomes. With the increase of gestational weight gain, the risk of preterm birth gradually decreased, but there was no statistical correlation between high gestational weight gain and preterm birth; with the increase of pre-pregnancy BMI and gestational weight gain, the risk of SGA gradually decreased, and the risk of LGA and caesarean section gradually increased; with the increase of pre-pregnancy BMI, the risk of GDM gradually increased, and insufficient gestational weight gain is associated with a higher risk of GDM, but there was no statistical correlation between high gestational weight gain and GDM.

Conclusions

There is a statistical correlation between pre-pregnancy BMI, gestational weight gain and adverse maternal and infant outcomes, unreasonable pre-pregnancy BMI and gestational weight gain will increase the risk of adverse gestational outcomes; there is a dose-response relationship between pre-pregnancy BMI, gestational weight gain and adverse maternal and infant outcomes, and there is a combined effect between pre-pregnancy BMI and gestational weight gain, and when guiding gestational weight gain, pre-pregnancy BMI should be comprehensively considered to prevent unreasonable gestational weight gain leading to the occurrence of adverse maternal and infant outcomes.