Early Pregnancy Overweight and Obesity and Infant Mortality
Early Pregnancy Overweight and Obesity and Infant Mortality
Objective. To investigate associations between maternal overweight and obesity and infant mortality outcomes, including cause-specific mortality.
Design. Population based cohort study.
Setting and Participants. 1,857,822 live single births in Sweden 1992–2010.
Main Outcome Measures. Associations between maternal body mass index (BMI) in early pregnancy and risks of infant, neonatal, and postneonatal mortality, overall and stratified by gestational length and by causes of infant death. Odds ratios were adjusted for maternal age, parity, smoking, education, height, country of birth, and year of delivery.
Results. Infant mortality rates increased from 2.4/1000 among normal weight women (BMI 18.5–24.9) to 5.8/1000 among women with obesity grade 3 (BMI ≥40.0). Compared with normal weight, overweight (BMI 25.0–29.9) and obesity grade 1 (BMI 30.0–34.9) were associated with modestly increased risks of infant mortality (adjusted odds ratios 1.25 (95% confidence interval 1.16 to 1.35) and 1.37 (1.22 to 1.53), respectively), and obesity grade 2 (BMI 35.0–39.9) and grade 3 were associated with more than doubled risks (adjusted odds ratios 2.11 (1.79 to 2.49) and 2.44 (1.88 to 3.17)). In analyses stratified by preterm and term births, maternal BMI was related to risks of infant mortality primarily in term births (≥37 weeks), where risks of deaths due to birth asphyxia and other neonatal morbidities increased with maternal overweight and obesity. Obesity grade 2–3 was also associated with increased infant mortality due to congenital anomalies and sudden infant death syndrome.
Conclusions. Maternal overweight and obesity are associated with increased risks of infant mortality due to increased mortality risk in term births and an increased prevalence of preterm births. Maternal overweight and obesity may be an important preventable risk factor for infant mortality in many countries.
The high prevalence of maternal overweight and obesity may have implications for infant health, as pregnancy complications such as pre-eclampsia and diabetic disorders are more common in these women. Maternal weight change between consecutive pregnancies correlates linearly with risks of these obesity related pregnancy complications, suggesting a causal relationship.
Pre-eclampsia is associated with intrauterine growth restriction and preterm delivery. Diabetic disorders increase the risk of congenital anomalies and may lead to macrosomia that increases the risk of birth trauma. Pregnancy complications probably explain the obesity related increased risk of medically indicated preterm delivery, but obese women are also at increased risk of spontaneous extremely preterm delivery (≤27 completed weeks).
Research on associations between maternal body mass index (BMI) and infant mortality has not produced consistent results. Two recently published meta-analyses disagree on whether infants of overweight mothers (BMI 25.0–29.9) are at increased risk, and only one of these meta-analyses investigated risks during the neonatal period. Other studies disagree on whether there are ethnic differences. Maternal obesity is known to increase the risk of infant deaths due to congenital anomalies, but research on associations with other specific causes of infant mortality is scarce.
A nationwide cohort of more than 1.8 million liveborn, singleton infants gave us the opportunity to test the hypothesis that maternal overweight and obesity are associated with infant, neonatal, and postneonatal mortality. As maternal BMI is positively associated with risk of preterm delivery, we also wanted to investigate these associations stratified by preterm and term births. Finally, we wanted to study whether maternal overweight and obesity are associated with specific causes of infant death.
Abstract and Introduction
Abstract
Objective. To investigate associations between maternal overweight and obesity and infant mortality outcomes, including cause-specific mortality.
Design. Population based cohort study.
Setting and Participants. 1,857,822 live single births in Sweden 1992–2010.
Main Outcome Measures. Associations between maternal body mass index (BMI) in early pregnancy and risks of infant, neonatal, and postneonatal mortality, overall and stratified by gestational length and by causes of infant death. Odds ratios were adjusted for maternal age, parity, smoking, education, height, country of birth, and year of delivery.
Results. Infant mortality rates increased from 2.4/1000 among normal weight women (BMI 18.5–24.9) to 5.8/1000 among women with obesity grade 3 (BMI ≥40.0). Compared with normal weight, overweight (BMI 25.0–29.9) and obesity grade 1 (BMI 30.0–34.9) were associated with modestly increased risks of infant mortality (adjusted odds ratios 1.25 (95% confidence interval 1.16 to 1.35) and 1.37 (1.22 to 1.53), respectively), and obesity grade 2 (BMI 35.0–39.9) and grade 3 were associated with more than doubled risks (adjusted odds ratios 2.11 (1.79 to 2.49) and 2.44 (1.88 to 3.17)). In analyses stratified by preterm and term births, maternal BMI was related to risks of infant mortality primarily in term births (≥37 weeks), where risks of deaths due to birth asphyxia and other neonatal morbidities increased with maternal overweight and obesity. Obesity grade 2–3 was also associated with increased infant mortality due to congenital anomalies and sudden infant death syndrome.
Conclusions. Maternal overweight and obesity are associated with increased risks of infant mortality due to increased mortality risk in term births and an increased prevalence of preterm births. Maternal overweight and obesity may be an important preventable risk factor for infant mortality in many countries.
Introduction
The high prevalence of maternal overweight and obesity may have implications for infant health, as pregnancy complications such as pre-eclampsia and diabetic disorders are more common in these women. Maternal weight change between consecutive pregnancies correlates linearly with risks of these obesity related pregnancy complications, suggesting a causal relationship.
Pre-eclampsia is associated with intrauterine growth restriction and preterm delivery. Diabetic disorders increase the risk of congenital anomalies and may lead to macrosomia that increases the risk of birth trauma. Pregnancy complications probably explain the obesity related increased risk of medically indicated preterm delivery, but obese women are also at increased risk of spontaneous extremely preterm delivery (≤27 completed weeks).
Research on associations between maternal body mass index (BMI) and infant mortality has not produced consistent results. Two recently published meta-analyses disagree on whether infants of overweight mothers (BMI 25.0–29.9) are at increased risk, and only one of these meta-analyses investigated risks during the neonatal period. Other studies disagree on whether there are ethnic differences. Maternal obesity is known to increase the risk of infant deaths due to congenital anomalies, but research on associations with other specific causes of infant mortality is scarce.
A nationwide cohort of more than 1.8 million liveborn, singleton infants gave us the opportunity to test the hypothesis that maternal overweight and obesity are associated with infant, neonatal, and postneonatal mortality. As maternal BMI is positively associated with risk of preterm delivery, we also wanted to investigate these associations stratified by preterm and term births. Finally, we wanted to study whether maternal overweight and obesity are associated with specific causes of infant death.
