IJE Advance Access originally published online on October 10, 2007
International Journal of Epidemiology 2007 36(6):1283-1284; doi:10.1093/ije/dym210
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Commentary: But why should women be weighed routinely during pregnancy?
1 Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Clarendon Way, Leeds, LS2 9JT, UK.
2 Bradford Institute for Health Research, Bradford Teaching Hospitals, NHS Foundation Trust, Duckworth Lane, Bradford, BD9 6RJ, UK.
* Corresponding author. Obstetric Epidemiology, Bradford Institute of Health research, Temple Bank House, Bradford Royal Infirmary, Duckworth Lane, Bradford, BD9 6RJ, UK. E-mail: diane.farrar{at}bradfordhospitals.nhs.uk
Accepted 24 September 2007
10.1093/ije/dym156
Kleinman and colleagues1 argue that the pattern of weight gain during pregnancy, as assessed by utilizing both the amount and timing of maternal weight in their area under the weight gain curve (AUC) method, is a more reliable predictor of weight retention after delivery than weight gain alone. Certainly, it seems plausible that weight gained early in pregnancy may be more difficult to shed, as this is likely to reflect maternal fat stores; rather than weight gained later in pregnancy which is more likely to be due to the growing fetus. Although this association may have a value for epidemiological analyses, does measuring maternal weight throughout pregnancy have a role in clinical practice?
Routine measurement of maternal weight was introduced into antenatal care during the Second World War in London, as a screening test for poor maternal nutrition. Decades later, the clinical value of this practice was challenged and found wanting.2 Although there is an association between maternal weight and birthweight,3 the AUC data1 provide further evidence that the correlation is too weak to be of clinical value. Nevertheless, maternal weight, weight gain and weight loss are associated with pregnancy outcome. Underweight women and those with weight loss during pregnancy have an increased risk of complications such as pre-term birth and low infant birthweight; whilst overweight women and those with excessive weight gain are at increased risk of a range of adverse outcomes, such as large for gestation babies, hypertension and diabetes.4 However, routine weighing as a screening test for low birthweight and other adverse pregnancy outcomes fails on the basic criteria of not having adequate sensitivity or specificity, and has the potential adverse effect of leading to unnecessary anxiety.
Routine weighing throughout pregnancy is no longer recommended in the UK.5 Instead, the advice is that women should be weighed at their first pregnancy care appointment, and the body mass index (BMI) calculated.5 Weighing is confined to this initial assessment, unless clinical management is likely to be influenced. In the USA, the Institute of Medicine recommendations6 are under review, but these currently state that pregnant women with risk factors such as low or high pre-pregnancy BMI or erratic weight gain should be weighed at each antenatal visit. As obesity for women aged 20–39 years in the USA is now 29%;7 this includes a substantial proportion of women.
A further limitation for measuring maternal weight, or weight for height, is the lack of evidence that intervention based on these measurements will improve outcome, for either mother or baby. The Cochrane review of trials evaluating energy and protein intake during pregnancy, for example, concludes that dietary advice appears to increase women's energy and protein intake, but is unlikely to confer major benefits in infant or maternal health.8 Balanced energy and protein supplementation does seem to improve fetal growth, and may reduce fetal and neonatal deaths.8 For obese women, or those with high weight gain during pregnancy, the review identified three trials (384 women) evaluating a low-energy diet (1200–2000 kcal/day) rather than a normal diet. Weekly maternal weight gain was reduced with the low-energy diet, but with no clear impact on either pregnancy-induced hypertension or pre-eclampsia. Of the two trials (282 women) reporting birthweight, one found little difference between the two groups, whilst the other found a substantial (450 g) reduction in birthweight associated with the low-energy diet. Although the reason for this difference in the impact on birthweight between the two trials is unclear, taken together, these results suggest women who are overweight or have high weight gain during pregnancy should not be advised to restrict their energy intake to this level. There is also a lack of evidence that exercise, or advice about exercise, during pregnancy impacts on outcome (three Cochrane reviews). Further research is needed to evaluate the potential effects of advice to alter diet and/or exercise during pregnancy.
Concern about the rapid and global rise in obesity has contributed to renewed interest in women's weight during pregnancy. In the United States, for example, the prevalence of obesity for women aged 20–39 years has risen 3-fold since 1960–627 and in Europe, there is concern that the increase in obesity is particularly alarming amongst children and adolescents.9 Alongside this epidemic of obesity, there is a culture that promotes ‘size zero’ as desirable. Women are inundated with images and information about body shape and size, along with advice about their diet and lifestyle: these messages often appear conflicting or inconsistent. What does now seem clearer is that changes in weight between pregnancies influences outcome of the next pregnancy. Data from cohort studies suggest women who increase their BMI by one or two units between pregnancies are at increased risk of a wide range of foetal and maternal adverse outcomes, including pre-eclampsia, gestational diabetes and large for gestational age babies.10 For larger increases in BMI, there is an association with increased stillbirth. These increases in adverse outcome are independent of whether the women are obese, or not. Women whose BMI falls by five or more units between pregnancies seem to have a higher risk of pre-term birth than those whose weight remained stable or increased.11
It would therefore seem sensible to encourage women to achieve and maintain an optimal weight before pregnancy, and to have a healthy diet and lifestyle during pregnancy. Routine weighing during pregnancy has not been demonstrated to have any direct benefit for either the woman or her child, and there are concerns it may lead to unnecessary anxiety. In the absence of evidence of benefit, women should not be required to have their weight measured throughout pregnancy, unless there is a specific clinical reason. If the sole purpose of weighing is for epidemiological research, this should be explained to women and they should have the option to decline.
Conflict of interest: None declared.
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1 Kleinman K, Oken E, Radesky JS, Rich-Edwards J, Peterson KE, Gillman M. How should gestational weight gain be assessed? A comparison of existing methods and a novel method, area under the weight gain curve. Int J Epidemiol (2007) 36:1275–83.
2 Dawes M, Grudzinskas J. Repeated measurement of maternal weight in pregnancy. Is this a useful practice? Br Jf Obstet Gynaecol (1991) 98:189–94.
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4 Walsh JM, Murphy D. Weight and pregnancy. Br Med J (2007) 335:169.
5 NICE. Antenatal Care Routine Care for the Healthy Pregnant Woman (2003) 6. London: Clinical Guideline.
6 Institute of Medicine. Nutrition During Pregnancy. Part I - Weight Gain. Part II - Nutrient Supplements (1990) Washington DC: National Academy Press.
7 Hedley A, Ogden CL, Johnson CL, Carroll MD, Curtin LR, Flegal KM. Prevalence of overweight and obesity among US children, adolescents, and Adults 1999–2002. JAMA (2004) 291:2847–50.
8 Kramer MS, Kakuma R. Energy and protein intake in pregnancy. Cochrane Db Syst Rev (2003) (Art. No.: CD000032. doi: 10.1002/14651858.CD000032.)
9 World Health Organisation Regional Office for Europe. Ministerial Conference on Counteracting Obesity. European charter on counteracting obesity,2006 [cited 2007]; Available at: http://www.euro.who.int/document/NUT/Obesity_Charter_E.pdf.
10 Villamor E, Cnattingius S. Interpregnancy weight change and risk of adverse pregnancy outcomes: a population-based study. Lancet (2006) 368:1164–70.[CrossRef][Medline]
11 Merlino A, Laffineuse L, Collin M, Mercer B. Impact of weight loss between pregnancies on recurrent preterm birth. Am J Obstet Gynecol (2006) 195:818.[CrossRef][Web of Science][Medline]
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