Pre-pregnancy body mass index, gestational weight gain, and other maternal characteristics in relation to infant birth weight.
OBJECTIVE
Infant birth weight is influenced by modifiable maternal pre-pregnancy behaviors and characteristics. We evaluated the relationship among pre-pregnancy body mass index (BMI), gestational weight gain, and infant birth weight, in a prospective cohort study.


METHODS
Women were enrolled at < or =20 weeks gestation, completed in-person interviews and had their medical records reviewed after delivery. Infant birth weight was first analyzed as a continuous variable, and then grouped into Low birth weight (LBW) (<2,500 g), normal birth weight (2,500-3,999 g), and macrosomia (> or =4,000 g) in categorical analysis. Pre-pregnancy BMI and gestational weight gain were categorized based on Institute of Medicine BMI groups and gestational weight gain guidelines. Associations among infant birth weight and pre-pregnancy BMI, gestational weight gain, and other factors were evaluated using multivariate regression. Risk ratios were estimated using generalized linear modeling procedures.


RESULTS
Pre-pregnancy BMI was independently and positively associated with infant birth weight (beta = 44.7, P = 0.001) after adjusting for confounders, in a quadratic model. Gestational weight gain was positively associated with infant birth weight (beta = 19.5, P < 0.001). Lower infant birth weight was associated with preterm birth (beta = -965.4, P < 0.001), nulliparity (beta = -48.6, P = 0.015), and female babies (beta = -168.7, P < 0.001). Less than median gestational weight gain was associated with twice the risk of LBW (RR = 2.04, 95% CI 1.34-3.11). Risk of macrosomia increased with increasing pre-pregnancy BMI and gestational weight gain (P for linear trend <0.001).


CONCLUSIONS
These findings support the need to balance pre-pregnancy weight and gestational weight gain against the risk of LBW and macrosomia among lean and obese women, respectively.
Frederick
Ihunnaya O
IO
Department of Health Services, University of Washington School of Public Health and Community Medicine, Seattle, WA, USA. ihunnaya.frederick@swedish.org
Williams
Michelle A
MA
Sales
Anne E
AE
Martin
Diane P
DP
Killien
Marcia
M
D000328:Adult; D001724:Birth Weight / Q000502:physiology*; D015992:Body Mass Index; D005260:Female; D005333:Fetus / Q000502:physiology*; D006801:Humans; D016015:Logistic Models; D011247:Pregnancy; D011256:Pregnancy Outcome; D015430:Weight Gain / Q000502:physiology*; D055815:Young Adult
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