Abstract: Background　Excessive or insufficient gestational weight gain（GWG） during pregnancy can increase the risk of adverse pregnancy outcomes，but whether the effects of GWG in different periods of pregnancy on perinatal outcomes are different are still inconclusive.Objective　This study aimed to analyze the effects of GWG in different pregnancy periods on risk of large for gestational age（LGA） and small for gestational age（SGA）.Methods　We conducted a cohort study using the baseline characteristics，GWG in different pregnancy periods and pregnancy outcomes collected from pregnant women.We enrolled a total of 15 334 participants who established a medical record for receiving healthcare at the first trimester of pregnancy and underwent regular antenatal care and delivered a singleton infant between June 1，2014 and May 31，2015 from Beijing Obstetrics and Gynecology Hospital，Capital Medical University.The effects of GWG on neonatal birth weight and corresponding population attributable risk（PAR%） were analyzed.Participants were classified to be underweight（<18.5 kg/m2，n=2 438），normal weight（18.5-24.9 kg/m2，n=11 052），overweight（25.0-29.9 kg/m2，n=1 600）and obese（≥30.0 kg/m2，n=244） according to WHO classification of prepregnancy BMI.GWG during 0-16 weeks of pregnancy was defined as the GWG in early pregnancy，because the formal medical record during pregnancy should be established within 16 weeks' gestation in our hospital.And the GWG during 17-28 weeks of pregnancy and 29 weeks of pregnancy to delivery was determined as the GWG in mid pregnancy，late pregnancy，respectively.Insufficient，normal and excess GWG during early and mid-pregnancy were defined by Institute of Medicine（IOM） average weight gain per week criteria.Results　Prevalences of LGA and SGA were 15.66%（2 401/15 334） and 2.93%（449/15 334），respectively.The total GWG for underweight，normal weight，overweight and obese groups was（16.2±4.7）kg，（15.8±4.9）kg，（13.6±5.5）kg and（10.8±5.8）kg，respectively.Approximately 27.62%（1 456/5 272），73.41%（3 870/5 272） and 49.89%（2 630/5 272） of women gained more weight in early，mid and late pregnancy，respectively，than that was recommended by IOM，while 50.89%（2 683/5 272），13.54%（714/5 272） and 31.83%（1 678/5 272） of women gained less weight than the lower limit of IOM recommendation.Multivariate Logistic regression analysis showed that excessive GWG was associated with an increased risk of LGA（P<0.001），while insufficient GWG in early pregnancy and mid-pregnancy was associated with an increased risk of SGA（P<0.001）.GWG in late pregnancy was not associated with risk of LGA or SGA（P>0.05）.GWG in mid-pregnancy contributed most to LGA in PAR%.Results from trend analyses showed that with the increase of GWG in early and mid pregnancy in all the participants，the risk of LGA increased（P<0.05）；with the increase of GWG in early and late pregnancy in underweight and normal weight participants，the risk of SGA decreased（P<0.05）.Conclusion　This study found that GWG during 0-16 weeks and 17-28 weeks of pregnancy had a significant effect on the risks of LGA and SGA.PAR% for LGA is highest in mid-pregnancy.Early and mid-pregnancy are critical periods of clinical intervention.This finding provides a big data foundation for the development of weight management programs during pregnancy.

Key words: Pregnancy；Body weight changes；Birth weight；Infant, small for gestational age；Large for gestational age；Root cause analysis

摘要： 背景　妊娠期增重过多或不足均可增加不良妊娠结局发生风险，但妊娠不同时期增重对围生结局的影响是否不同目前尚无定论。目的　本研究拟分析比较妊娠不同时期增重对大于胎龄儿（LGA）和小于胎龄儿（SGA）发生风险的影响。方法　选取妊娠早期在首都医科大学附属北京妇产医院建档并接受规律产检，于2014-06-01至2015-05-31在本院分娩的单胎孕妇，共纳入15 334例。采用队列研究的方法，收集孕妇基线信息、妊娠期增重情况及分娩结局，分析妊娠不同时期增重对新生儿出生体质量的影响。按照世界卫生组织（WHO）标准将孕妇按照妊娠前体质指数（BMI）分为4组：低体质量组（<18.5 kg/m2，n=2 438），正常体质量组（18.5~24.9 kg/m2，n=11 052），超重组（25.0~29.9 kg/m2，n=1 600）及肥胖组（≥30.0 kg/m2，n=244）。由于本院产检建档时间为妊娠16周，因此按照0~16周（妊娠早期）、17~28周（妊娠中期）及29周至分娩（妊娠晚期）计算各期增重。根据美国医学研究所（IOM）推荐的妊娠早期及妊娠中期平均每周增重标准，按照具体孕周对不同BMI组妊娠期增重划分为增重不足、增重适宜及增重过多。结果　15 334例孕妇中LGA发生率为15.66%（2 401/15 334），而SGA发生率为2.93%（449/15 334）。低体质量组、正常体质量组、超重组和肥胖组妊娠期总增重分别为（16.2±4.7）kg、（15.8±4.9）kg、（13.6±5.5）kg和（10.8±5.8）kg，分别有27.62%（1 456/5 272）、73.41%（3 870/5 272）及49.89%（2 630/5 272）的孕妇在妊娠早期、妊娠中期和妊娠晚期增重过多，而50.89%（2 683/5 272）、13.54%（714/5 272）及31.83%（1 678/5 272）的孕妇在此3个阶段增重不足。多因素Logistic回归分析结果显示，妊娠早期、妊娠中期增重过多增加LGA发生风险（P<0.001），增重不足增加SGA发生风险（P<0.001）；妊娠晚期增重情况对SGA、LGA的发生无影响（P>0.05）。其中，妊娠中期增重过多对LGA发生的人群归因危险度百分比（PAR%）最高。低体质量组、正常体质量组、超重肥胖组在妊娠早期、妊娠中期随着增重增加，LGA发生风险升高（P<0.05）。低体质量组、正常体质量组在妊娠早期、妊娠晚期随着增重增加，SGA发生风险降低（P<0.05）。结论　妊娠早期及妊娠中期增重与LGA及SGA发生风险均相关，其中妊娠中期增重过多的比例最高，LGA发生的PAR%也最高。妊娠早、中期是临床干预的关键时期，这一发现为妊娠期体质量管理方案的制定提供了大数据基础。

关键词: 妊娠；体重变化；出生体重；婴儿, 小于胎龄；大于胎龄儿；影响因素分析