Am J Epidemiol. 2022 Sep 28;191(10):1687-1699. doi: 10.1093/aje/kwac120.
Cross-sectional studies of total gestational weight gain (GWG) and perinatal outcomes have used different approaches to operationalize GWG and adjust for duration of gestation. Using birth records from California (2007-2017), Nevada (2010-2017), and Oregon (2008-2017), we compared 3 commonly used approaches to estimate associations between GWG and cesarean delivery, small-for-gestational-age birth, and low birth weight (LBW): 1) the Institute of Medicine-recommended GWG ranges at a given gestational week, 2) total weight gain categories directly adjusting for gestational age as a covariate, and 3) weight-gain-for-gestational-age z scores derived from an external longitudinal reference population. Among 5,461,130 births, the 3 methods yielded similar conclusions for cesarean delivery and small-for-gestational-age birth. However, for LBW, some associations based on z scores were in the opposite direction of methods 1 and 2, paradoxically suggesting that higher GWG increases risk of LBW. This was due to a greater proportion of preterm births among those with high z scores, and controlling for gestational age in the z score model brought the results in line with the other methods. We conclude that the use of externally derived GWG z scores based on ongoing pregnancies can yield associations confounded by duration of pregnancy when the outcome is strongly associated with gestational age at delivery.
横断面研究总孕期体重增加（GWG）和围产期结局使用了不同的方法来操作 GWG 并调整妊娠持续时间。我们使用来自加利福尼亚州（2007-2017 年）、内华达州（2010-2017 年）和俄勒冈州（2008-2017 年）的出生记录，比较了 3 种常用于估计 GWG 与剖宫产、小于胎龄儿出生和低出生体重（LBW）之间关联的方法：1）医学研究所推荐的在特定孕周的 GWG 范围，2）直接调整为协变量的总体重增加类别，以及 3）源自外部纵向参考人群的体重增加-胎龄 z 分数。在 5461130 例分娩中，这 3 种方法对于剖宫产和小于胎龄儿出生得出了相似的结论。然而，对于 LBW，一些基于 z 分数的关联方向与方法 1 和 2 相反，矛盾地表明较高的 GWG 增加了 LBW 的风险。这是由于高 z 分数者中早产儿的比例较高，并且在 z 分数模型中控制了胎龄，使结果与其他方法一致。我们得出结论，当结局与分娩时的胎龄密切相关时，使用基于正在进行的妊娠的外部衍生的 GWG z 分数可能会因妊娠持续时间而产生混淆关联。
