Regular weighing of pregnant women: a relic from a bygone era

IF 4.2 2区 医学 Q1 ENDOCRINOLOGY & METABOLISM Obesity Pub Date : 2024-07-28 DOI:10.1002/oby.24117
Jodie M. Dodd, Andrea R. Deussen, Megan Mitchell, Jennie Louise
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However, this practice is not universal, with other countries adopting a more intensive approach with regular weighing at each antenatal appointment and adherence to the Institute of Medicine (now National Academy of Medicine) recommendations to limit gestational weight gain (GWG), with the expectation of improved pregnancy and birth outcomes [<span>(4)</span>].</p><p>In this edition, Boone-Heinonen and colleagues [<span>(5)</span>] report a cohort study using electronic health record data from 77,599 pregnancies between 2004 and 2020 from women whose body mass index (BMI) was greater than 18.5 kg/m<sup>2</sup>. GWG was measured in each trimester of pregnancy to evaluate relationships between rate of gain and the occurrence of infant size at birth, defined as large for gestational age (LGA; &gt;90th percentile) and SGA (&lt;10th percentile). The authors identified the risk of birth of an infant with LGA to be greatest among women with a higher prepregnancy BMI and among those whose GWG was higher. Conversely, birth of an infant with SGA was seen in women with a lower prepregnancy BMI and lower GWG. The authors suggest that first-trimester GWG may influence birth size via an effect on second- and third-trimester weight gain and that targeting first-trimester weight gain may be a strategy for intervention.</p><p>We would like to propose an alternate view that challenges some of the widely held assumptions around GWG and its relationship, often presumed to be causal, with pregnancy and birth outcomes. Recent reports [<span>(6-8)</span>] have identified the lack of evidence to suggest that the effect of maternal BMI on pregnancy outcomes is mediated via an effect on GWG. That is, GWG is not on a causal pathway between maternal BMI and adverse pregnancy outcomes [<span>(6)</span>], with limited predictive value in the identification of women who experience a range of pregnancy and birth complications [<span>(7, 8)</span>].</p><p>The validity of the purported relationships between total or trimester-specific GWG and fetal size is problematic for reasons that should be immediately apparent in considering the nature of GWG as an outcome. Although GWG is a clinically simple measure to obtain, it represents a composite of maternal fat deposition; pregnancy-related plasma volume expansion; breast and uterine tissue hypertrophy; extracellular fluid; and the products of pregnancy, including the placenta, fetus, and amniotic fluid. Furthermore, the precise contribution from each of these components in an individual woman is extremely difficult to measure with any degree of accuracy. Be that as it may, any relationship between GWG and birth weight cannot be a causal relationship by definition because fetal weight is a component of GWG. This means that, necessarily, if two women are equal in all other aspects of each of the GWG components as outlined earlier, but the first fetus weighs more than the second fetus (including weight for gestational age), the first woman will necessarily have greater GWG. The only possible interpretation of the relationship between GWG and infant birth size is that women with a larger fetus give birth to larger babies.</p><p>Furthermore, the lack of a causal association between maternal BMI and GWG not only suggests that GWG is not an appropriate target to improve pregnancy outcomes but also potentially explains the very limited clinical impact of antenatal pregnancy interventions that have been observed to date. 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Abstract

The practice of regularly weighing women during pregnancy dates to the 1940s in a strategy introduced by the government of the UK to monitor the effect of post-World War II food rationing on the maintenance of a healthy pregnancy [(1)]. This practice continued throughout the 1970s and into the 1990s to aid detection of both preeclampsia and infants who are born small for gestational age (SGA), although it was recognized to have a low positive predictive value [(2)]. There has since been a move in some countries [(3)] to recommend that a woman be weighed only at the time of the booking obstetric visit in the first trimester and then again at 36 weeks' gestation. However, this practice is not universal, with other countries adopting a more intensive approach with regular weighing at each antenatal appointment and adherence to the Institute of Medicine (now National Academy of Medicine) recommendations to limit gestational weight gain (GWG), with the expectation of improved pregnancy and birth outcomes [(4)].

In this edition, Boone-Heinonen and colleagues [(5)] report a cohort study using electronic health record data from 77,599 pregnancies between 2004 and 2020 from women whose body mass index (BMI) was greater than 18.5 kg/m2. GWG was measured in each trimester of pregnancy to evaluate relationships between rate of gain and the occurrence of infant size at birth, defined as large for gestational age (LGA; >90th percentile) and SGA (<10th percentile). The authors identified the risk of birth of an infant with LGA to be greatest among women with a higher prepregnancy BMI and among those whose GWG was higher. Conversely, birth of an infant with SGA was seen in women with a lower prepregnancy BMI and lower GWG. The authors suggest that first-trimester GWG may influence birth size via an effect on second- and third-trimester weight gain and that targeting first-trimester weight gain may be a strategy for intervention.

We would like to propose an alternate view that challenges some of the widely held assumptions around GWG and its relationship, often presumed to be causal, with pregnancy and birth outcomes. Recent reports [(6-8)] have identified the lack of evidence to suggest that the effect of maternal BMI on pregnancy outcomes is mediated via an effect on GWG. That is, GWG is not on a causal pathway between maternal BMI and adverse pregnancy outcomes [(6)], with limited predictive value in the identification of women who experience a range of pregnancy and birth complications [(7, 8)].

The validity of the purported relationships between total or trimester-specific GWG and fetal size is problematic for reasons that should be immediately apparent in considering the nature of GWG as an outcome. Although GWG is a clinically simple measure to obtain, it represents a composite of maternal fat deposition; pregnancy-related plasma volume expansion; breast and uterine tissue hypertrophy; extracellular fluid; and the products of pregnancy, including the placenta, fetus, and amniotic fluid. Furthermore, the precise contribution from each of these components in an individual woman is extremely difficult to measure with any degree of accuracy. Be that as it may, any relationship between GWG and birth weight cannot be a causal relationship by definition because fetal weight is a component of GWG. This means that, necessarily, if two women are equal in all other aspects of each of the GWG components as outlined earlier, but the first fetus weighs more than the second fetus (including weight for gestational age), the first woman will necessarily have greater GWG. The only possible interpretation of the relationship between GWG and infant birth size is that women with a larger fetus give birth to larger babies.

Furthermore, the lack of a causal association between maternal BMI and GWG not only suggests that GWG is not an appropriate target to improve pregnancy outcomes but also potentially explains the very limited clinical impact of antenatal pregnancy interventions that have been observed to date. In contrast, maternal prepregnancy BMI has been identified to be causally related to adverse pregnancy outcomes [(6, 8)], with the risk increasing with increasing BMI [(6)]. This suggests that preconception interventions may be a more appropriate target for intervention to improve pregnancy outcomes for women and their infants.

An ongoing and relentless search for the “right” antenatal intervention targeting GWG as being on a causal pathway to improved clinical pregnancy and birth outcomes would seem to be an exercise in futility. Not only does such an approach unnecessarily waste limited health care resources, but it also sets women up to fail in their inability to meet unattainable goals. Rather than continuing to focus on GWG, researchers and clinicians should reconsider the validity of such an approach and the practice of actively managing GWG throughout pregnancy.

The authors declared no conflict of interest.

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孕妇定期称重:过去时代的遗物。
定期为孕期妇女称重的做法可以追溯到 20 世纪 40 年代,当时英国政府为监测二战后粮食配给对维持健康妊娠的影响而引入了这一策略[(1)]。这种做法一直持续到 20 世纪 70 年代和 90 年代,以帮助检测子痫前期和出生时胎龄偏小的婴儿(SGA),尽管这种方法的阳性预测值较低[(2)]。此后,一些国家[(3)]建议仅在妊娠头三个月的产科预约就诊时为孕妇称重,然后在妊娠 36 周时再次称重。然而,这种做法并不普遍,其他一些国家则采取了更严格的方法,在每次产前检查时定期称重,并遵守美国医学研究所(现为美国国家医学研究院)关于限制妊娠体重增加(GWG)的建议,以期改善妊娠和分娩结局[(4)]。在本版中,Boone-Heinonen 及其同事[(5)]报告了一项队列研究,该研究使用了 2004 年至 2020 年期间 77,599 名孕妇的电子健康记录数据,这些孕妇的体重指数(BMI)大于 18.5 kg/m2。在妊娠的每个三个月都测量了孕妇的体重增加率(GWG),以评估增加率与婴儿出生时体型大小之间的关系,婴儿出生时体型大小被定义为胎龄偏大(LGA;第 90 百分位数)和 SGA(第 10 百分位数)。作者发现,孕前体重指数(BMI)较高的妇女和胎龄较大的妇女生出 LGA 婴儿的风险最大。相反,孕前体重指数(BMI)较低和 GWG 较低的妇女生出 SGA 婴儿的风险较高。作者认为,第一胎 GWG 可能会通过影响第二胎和第三胎的体重增加来影响胎儿的出生大小,针对第一胎的体重增加可能是一种干预策略。我们想提出另一种观点,对围绕 GWG 及其与妊娠和分娩结果的关系(通常被假定为因果关系)的一些普遍假设提出质疑。最近的报告[(6-8)]指出,缺乏证据表明孕产妇体重指数对妊娠结局的影响是通过对 GWG 的影响而介导的。也就是说,GWG 并不是孕产妇体重指数(BMI)与不良妊娠结局之间的因果关系[(6)],对识别出现一系列妊娠和分娩并发症的妇女的预测价值有限[(7, 8)]。虽然 GWG 在临床上很容易获得,但它代表了母体脂肪沉积、与妊娠相关的血浆体积膨胀、乳房和子宫组织肥大、细胞外液以及妊娠产物(包括胎盘、胎儿和羊水)的综合结果。此外,要精确测量每个妇女体内这些成分的确切贡献是非常困难的。尽管如此,GWG 与出生体重之间的任何关系都不可能是因果关系,因为胎儿体重是 GWG 的一个组成部分。这就意味着,如果两名妇女在前面概述的 GWG 各组成部分的所有其他方面都相同,但第一个胎儿的体重(包括胎龄体重)大于第二个胎儿的体重,则第一个妇女的 GWG 必然较大。此外,孕产妇体重指数(BMI)与 GWG 之间缺乏因果关系,这不仅表明 GWG 并不是改善妊娠结局的适当目标,而且也可能解释了迄今为止观察到的产前妊娠干预的临床影响非常有限的原因。相比之下,孕产妇孕前体重指数(BMI)被认为与不良妊娠结局有因果关系[(6, 8)],随着体重指数(BMI)的增加,风险也随之增加[(6)]。持续不懈地寻找 "正确的 "产前干预措施,将 GWG 作为改善临床妊娠和分娩结局的因果途径,似乎是徒劳无益的。这种做法不仅不必要地浪费了有限的医疗资源,而且还会使妇女因无法实现遥不可及的目标而陷入失败的境地。研究人员和临床医生不应继续关注 GWG,而应重新考虑这种方法的有效性以及在整个孕期积极管理 GWG 的做法。
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来源期刊
Obesity
Obesity 医学-内分泌学与代谢
CiteScore
11.70
自引率
1.40%
发文量
261
审稿时长
2-4 weeks
期刊介绍: Obesity is the official journal of The Obesity Society and is the premier source of information for increasing knowledge, fostering translational research from basic to population science, and promoting better treatment for people with obesity. Obesity publishes important peer-reviewed research and cutting-edge reviews, commentaries, and public health and medical developments.
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