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Published on: August 7, 2017
Association of birth weight with asthma-related outcomes at age 2 years
Elsie M Taveras1, Carlos A Camargo, Sheryl L Rifas-Shiman
1Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, Massachusetts 02215, USA. Elsie.Taveras@childrens.harvard.edu
Insights
Higher birth weight and longer gestation did not increase childhood asthma risk in this study. Factors like male sex, passive smoking, and family history of asthma were linked to increased wheezing and asthma diagnoses by age 2.
Area of Science:
- Pediatric Allergy and Immunology
- Neonatal Health
- Epidemiology
Background:
- Lower birth weight, often linked to prematurity, is a known risk factor for childhood asthma.
- Few studies have investigated the impact of higher birth weight on asthma development.
- Research has rarely distinguished between fetal growth and gestational length as separate contributors to birth weight and subsequent asthma risk.
Purpose of the Study:
- To investigate the association between fetal growth and length of gestation with asthma-related outcomes up to age 2 years.
- To clarify the independent contributions of fetal growth and gestational duration to childhood asthma risk.
- To examine risk factors for wheezing and asthma in early childhood.
Main Methods:
- A prospective cohort study (Project Viva) involving 1,372 infants born after 34 weeks gestation.
- Asthma-related outcomes assessed via parent reports of wheezing (any and recurrent) and doctor-diagnosed asthma by age 2.
- Gestational age and fetal growth (birth weight z-value) were calculated using standardized methods.
Main Results:
- No significant association was found between higher birth weight (≥4,000g) and increased odds of wheezing or doctor-diagnosed asthma by age 2.
- Neither the highest nor lowest categories of fetal growth or length of gestation were linked to asthma-related outcomes.
- Male sex, passive smoking exposure, parental asthma history, and presence of older siblings were associated with higher risks of wheezing and asthma.
Conclusions:
- Fetal growth and length of gestation were not associated with increased risk of wheezing or asthma by age 2 in children born after 34 weeks gestation.
- Male sex, passive smoking, parental asthma history, and exposure to older siblings are significant risk factors for early childhood asthma.
- This study highlights key environmental and genetic factors influencing childhood asthma development.
Background:
Although lower birth weight associated with prematurity raises the risk of asthma in childhood, few prospective studies have examined higher birth weight, and few have separated the two components of birth weight, fetal growth and length of gestation.
Objective:
To examine the associations of fetal growth and length of gestation with asthma-related outcomes by age 2 years.
Methods:
We studied 1,372 infants and toddlers born after 34 weeks' gestation in Project Viva, a prospective cohort study of pregnant mothers and their children. The main outcome measures were parent report of (1) any wheezing (or whistling in the chest) from birth to age 2 years, (2) recurrent wheezing during the first 2 years of life, and (3) doctor's diagnosis of asthma, wheeze or reactive airway disease ("asthma") by age 2. We calculated gestational age from the last menstrual period or ultrasound examination, and determined birth weight for gestational age z-value ("fetal growth") using US national reference data.
Results:
Infants' mean birth weight was 3,527 (SD, 517; range, 1,559-5,528) grams. By age 2 years, 34% of children had any wheezing, 14% had recurrent wheezing, and 16% had doctor-diagnosed asthma. After adjusting for several parent, child, and household characteristics in logistic regression models, we found that infants with birth weight > or = 4,000 g were not more likely to have any wheezing (odds ratio (OR), 0.91; 95% confidence interval (CI): 0.62, 1.34) or doctor-diagnosed asthma (OR, 0.80; 95% CI: 0.49, 1.31) than infants with birth weight 3,500-3,999 g. In models examining length of gestation and fetal growth separately, neither the highest nor the lowest groups of either predictor were associated with the three outcomes. Boys had a higher incidence of asthma-related outcomes than girls, and exposure to passive smoking, parental history of asthma, and exposure to older siblings were all associated with greater risk of recurrent wheeze or asthma-related outcomes at age 2 years.
Conclusion:
Although male sex, exposure to smoking, parental history of asthma, and exposure to older siblings were associated with increased risk of wheezing and asthma-related outcomes in this prospective study of children born after 34 weeks gestation, fetal growth and length of gestation were not.
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