Original Articles
Why are babies getting bigger? Temporal trends in fetal growth and its determinants,☆☆,

https://doi.org/10.1067/mpd.2002.128029Get rights and content

Abstract

Objectives: To describe temporal trends in fetal “growth” and to examine the roles of sociodemographic, anthropometric, and other determinants. Study design: Hospital-based cohort study of 61,437 nonmalformed singleton live births at 22 to 43 weeks' gestational age. Four main measures were examined: (1) birth weight, (2) birth weight-for-gestational-age Z score, (3) small-for-gestational-age (SGA), and (4) large-for-gestational age (LGA), with the latter 3 measures based on a recently developed population-based Canadian reference. Gestational age was based on the last normal menstrual period if confirmed (± 1 week) by early ultrasonogram. Results: The mean birth weight and Z score increased significantly (P <.0001) among infants ≥37 weeks, with a corresponding reduction in % SGA and a rise in % LGA. No consistent trends were seen among births 34 to 36 or ≤33 weeks. When simultaneous changes in maternal prepregnancy body mass index, gestational weight gain, height, cigarette smoking, and other clinical and sociodemographic factors were controlled by using multiple logistic regression, the temporal trends for term infants were no longer evident. Conclusions: Increases in maternal anthropometry, reduced cigarette smoking, and changes in sociodemographic factors have led to an increase in the weight of infants born at or after term. (J Pediatr 2002;141:538-42)

Section snippets

Methods

We designed a hospital-based historical cohort study at the Royal Victoria Hospital, a McGill University teaching hospital with a clinically detailed computerized obstetric and neonatal database that has been maintained since January 1, 1978.12 This study is based on 61,437 inborn, nonmalformed singleton live births of 22 to 43 weeks' gestational age without antenatal transfer, who were delivered between January 1, 1978 and March 31, 1996. We excluded both antenatal transfers and outborn

Results

Table I shows the trends in mean birth weight, mean birth weight-for-gestational-age Z score, and SGA and LGA proportions in singleton live births ≥37 completed weeks.

. Temporal trends in mean birth weight, mean Z score, and SGA and LGA proportions among singleton live births ≥37 completed weeks (n = 57,199)

PeriodnMean Birth weight (g)MeanZ score% SGA% LGA
1978-7956263419−0.09111.18.0
1980-8156593426−0.04610.38.4
1982-83633334530.0138.99.9
1984-85622234490.0508.210.0
1986-87619234650.1027.811.2
1988-89

Discussion

The observed temporal trends in mean birth weight, mean birth weight-for-gestational age Z score, SGA, and LGA proportions all indicate an increase in fetal growth between 1978 and 1996 at this tertiary-care Montreal teaching hospital. As hypothesized, the increase was restricted to births ≥37 weeks (except for an inexplicable rise in LGA birth among infants ≤33 weeks), and the increase was largely the result of a rise in prepregnancy BMI, gestational weight gain, and gestational diabetes and

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Drs Kramer, Platt, Joseph, and Wen are recipients of career investigator awards from the Canadian Institutes of Health Research.

☆☆

Dr Joseph is also a Clinical Scholar of the Dalhousie University Faculty of Medicine.

Reprint requests: Michael S. Kramer, MD, 2300 Tupper St, Montréal, Québec, Canada H3H 1P3.

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