Abstract
Estimation of pre-pregnancy weight is difficult because measurements taken before pregnancy are rarely available. No studies have compared various 'proxy' measures using recalled weight or based on early pregnancy weight with actual measurements of pre-pregnancy weight. The Southampton Women's Survey recruited women during 1998-2002 who were not pregnant. Data on 198 women with an estimated date of conception within 3 months of recruitment were analysed. Three proxy measures were considered: (1) recalled pre-pregnancy weight obtained during early pregnancy, (2) measured weight in early pregnancy and (3) estimated pre-pregnancy weight using a published model. Mean (standard deviation) recalled weight was 1.65 (3.03) kg lighter than measured pre-pregnancy weight, while early pregnancy weight and weights from the published model were 0.88 (2.34) and 0.88 (2.33) kg heavier, respectively. The Bland-Altman limits of agreement for recalled weight were -7.59 to 4.29 kg, wider than those for the early pregnancy weight: -3.71 to 5.47 kg and the published model: -3.68 to 5.45 kg. For estimating pre-pregnancy weight, we recommend subtraction of 0.88 kg from early pregnancy weight or the published model, or addition of 1.65 kg to recalled weight. Estimates of pre-pregnancy body mass index and gestational weight gain categories were very similar when using early pregnancy and published model weights, but they differed from those using recalled weight. Our findings indicate that calculations of first trimester weight gain using recalled weight must be treated cautiously, and a measured weight in early pregnancy provides a more precise assessment of pre-pregnancy weight than recalled weight.
Highlights
As prevalence rates of overweight and obesity have risen, there has been an increasing focus on maternal pre-pregnancy overweight and obesity and excessive gestational weight gain (GWG) in relation both to the effects on women themselves and their children.[1,2] Clinically, there is concern about women entering pregnancy affected by overweight or obesity, not least in relation to the associated risks of gestational diabetes and poor birth outcomes.[1]
We considered three estimates of this measure, namely the pre-pregnancy weight recalled by each woman, the weight measured in early pregnancy and a pre-pregnancy weight estimated according to the formula of Thomas et al.:[29] y 1⁄4 6:10 þ 0:99x1 À 0:01x2 À 0:02x3 À 0:04x4 À 0:09x5 where y = pre-pregnancy weight
The 198 participants had a wide range of pre-pregnancy weights (40–119 kg), and the body mass index (BMI) range was 16.4–43.6 kg/m2, with 6 (3%) women being affected by underweight (BMI < 18.5 kg/m2), 43 (22%) by overweight (BMI between 25 and 30 kg/m2) and a further 37 (19%) by obesity, (BMI greater than 30 kg/m2)
Summary
As prevalence rates of overweight and obesity have risen, there has been an increasing focus on maternal pre-pregnancy overweight and obesity and excessive gestational weight gain (GWG) in relation both to the effects on women themselves and their children.[1,2] Clinically, there is concern about women entering pregnancy affected by overweight or obesity, not least in relation to the associated risks of gestational diabetes and poor birth outcomes.[1]. In 1990, the Institute of Medicine (IOM) produced guidelines for weight gain during pregnancy,[21] with the recommended amount of weight gain varying according to pre-pregnancy body mass index (BMI). These guidelines were revised in 200922 and are used widely in clinical practice and research for categorising GWG as inadequate, adequate or excessive. The 1990 guidelines included guidance on assessment of GWG and recommended that pre-pregnancy weight is best determined from a weight measured at a recent preconceptional visit and that self-reported pre-pregnancy weights must be evaluated for plausibility and discarded if they are suspect.
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