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A nearly continuous measure of birth weight for gestational age using a United States national reference
Emily Oken1, Ken P Kleinman, Janet Rich-Edwards
1Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, USA. emily_oken@hphc.org
Insights
This study created detailed birth weight references for each week of gestation (22-44 weeks) using US natality data. These comprehensive fetal growth charts aid research into birth weight determinants and outcomes.
Area of Science:
- Perinatal epidemiology
- Fetal growth research
- Public health statistics
Background:
- Accurate fetal growth assessment requires birth weight adjusted for gestational age.
- Existing US reference data offers limited percentiles, hindering detailed analysis.
- Need for continuous birth weight reference measures for epidemiologic studies.
Purpose of the Study:
- To generate continuous, week-by-week reference measures for birth weight adjusted for gestational age.
- To provide comprehensive reference data for fetal growth from 22 to 44 weeks of gestation.
- To support epidemiologic analyses of fetal growth determinants and sequelae.
Main Methods:
- Utilized nationwide US Natality datasets from 1999-2000.
- Analyzed data from over 6.6 million singleton births.
- Generated multiple birth weight percentiles for each completed week of gestation (22-44 weeks).
Main Results:
- Birth weight increased with gestational age, with accelerated growth in the third trimester.
- Identified significant differences in birth weight based on sex, birth order, and maternal race/ethnicity.
- Observed patterns align with previous findings but offer greater detail.
Conclusions:
- Developed comprehensive birth weight references for 22-44 weeks gestation using extensive national data.
- This method avoids assumptions of normality or specific functional relationships, offering broader applicability.
- These detailed references are valuable for researchers studying fetal growth predictors and outcomes.
Background:
Fully understanding the determinants and sequelae of fetal growth requires a continuous measure of birth weight adjusted for gestational age. Published United States reference data, however, provide estimates only of the median and lowest and highest 5th and 10th percentiles for birth weight at each gestational age. The purpose of our analysis was to create more continuous reference measures of birth weight for gestational age for use in epidemiologic analyses.
Methods:
We used data from the most recent nationwide United States Natality datasets to generate multiple reference percentiles of birth weight at each completed week of gestation from 22 through 44 weeks. Gestational age was determined from last menstrual period. We analyzed data from 6,690,717 singleton infants with recorded birth weight and sex born to United States resident mothers in 1999 and 2000.
Results:
Birth weight rose with greater gestational age, with increasing slopes during the third trimester and a leveling off beyond 40 weeks. Boys had higher birth weights than girls, later born children higher weights than firstborns, and infants born to non-Hispanic white mothers higher birth weights than those born to non-Hispanic black mothers. These results correspond well with previously published estimates reporting limited percentiles.
Conclusions:
Our method provides comprehensive reference values of birth weight at 22 through 44 completed weeks of gestation, derived from broadly based nationwide data. Other approaches require assumptions of normality or of a functional relationship between gestational age and birth weight, which may not be appropriate. These data should prove useful for researchers investigating the predictors and outcomes of altered fetal growth.