Evidence-Based Medicine Online First, published on February 19, 2015 as 10.1136/ebmed-2014-110163 Aetiology
Cohort study
Maternal overweight and obesity in early pregnancy are associated with an increase in infant mortality risk 10.1136/ebmed-2014-110163
Rebecca M Reynolds Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, UK Correspondence to: Professor Rebecca Reynolds, Endocrinology Unit, University/BHF Centre for Cardiovascular Science, Queen’s Medical Research Institute, Edinburgh, EH16 4TJ, UK; [email protected]
Commentary on: Johansson S, Villamor E, Altman M, et al. Maternal overweight and obesity in early pregnancy and risk of infant mortality: a population based cohort study in Sweden. BMJ 2014;349:g6572.
with maternal overweight and obesity. Obesity grades II–III (BMI ≥35) was also associated with increased infant mortality due to congenital anomalies and sudden infant death syndrome.
Commentary This study demonstrates that maternal overweight, as well as maternal obesity is associated with increased infant mortality risk and the risk increases with increasing BMI.1 2 The excess mortality is explained by an increased mortality risk in term births, due to birth asphyxia and other neonatal morbidities, including congenital anomalies, and also by an increased prevalence of preterm births. This study adds to our knowledge of the adverse effects of maternal overweight and obesity in pregnancy on offspring outcomes3 and is of concern given the high prevalence of maternal overweight and obesity.4 Indeed Sweden has one of lowest rates of infant mortality in the world5 so outcomes may be worse in areas where antenatal care is not as good. The main strength of the study was the large, population-based approach with prospectively collected data and adjustments for several confounders including surrogates of socioeconomic status. The study raises the question of what we can do to improve outcomes. Ideally, overweight or obese women should be encouraged to lose weight before pregnancy, but this may be challenging to achieve. Information about gestational weight gain was not available in the study and this may be an area to target. Trials of lifestyle intervention during pregnancy6 7 or pharmacological interventions that limit gestational weight gain8 are ongoing and results are eagerly awaited.
Context Rates of overweight and obesity among women of childbearing age are increasing worldwide. This has implications for infant health as pregnancy complications, including preeclampsia and gestational diabetes, are more common in women with a higher body mass index (BMI) and there may be more indications for medical preterm delivery. Findings from studies testing associations between maternal BMI and infant mortality are inconsistent, with little information on specific causes of infant mortality. This study used a large nationwide cohort to test associations between maternal BMI and infant, neonatal and postneonatal mortality outcomes, including cause-specific mortality.
Implications for practice The study highlights the need for public health messages to emphasise the importance of a healthy weight for pregnancy. In addition, healthcare professionals should be alerted to the need for careful monitoring of overweight and obese women during pregnancy to ensure optimal outcome for mother and baby. Competing interests None. Provenance and peer review Commissioned; internally peer reviewed.
Methods This was a population-based cohort study including 1 857 822 live single births in Sweden from 1992 to 2010. Maternal BMI was calculated from self-reported height and weight measured at the first antenatal visit. Infant, neonatal and postneonatal mortality were defined as infant deaths during the first year of life, within and after the first 28 days of life, respectively. Overall mortality rates (deaths per 1000 liveborn infants) were calculated and stratified by gestational length and by specific causes of infant death according to International Classification of Diseases codes. ORs were adjusted for maternal age, parity, smoking, education, height, country of birth and year of delivery.
Findings Infant mortality rates increased from 2.4/1000 among normal weight women (BMI 18.5–24.9) to 5.8/1000 among women with grade III obesity (BMI ≥40). Compared with normal weight, overweight (BMI 25.0–29.9) and grade I obesity (BMI 30–34.9) were also associated with modestly increased risks of infant mortality (adjusted ORs 1.25 (95% CI 1.16 to 1.35) and 1.37 (95% CI 1.22 to 1.53)) with more than doubling the risk at higher BMI levels. In stratified analyses, maternal BMI was related to infant mortality primarily in term births (≥37 weeks) where risks of deaths due to birth asphyxia and other neonatal morbidities increased
References 1. Meehan S, Beck CR, Mair-Jenkins J, et al. Maternal obesity and infant mortality: a meta-analysis. Pediatrics 2014;133:863–71. 2. Aune D, Saugstad OD, Henriksen T, et al. Maternal body mass index and the risk of fetal death, stillbirth, and infant death: a systematic review and meta-analysis. JAMA 2014;311:1536–46. 3. Reynolds RM, Allan KM, Raja EA, et al. Maternal obesity during pregnancy and premature mortality from cardiovascular event in adult offspring: follow-up of 1,323,275 person years. BMJ 2013;347:f4539. 4. Heslehurst N, Rankin J, Wilkinson JR, et al. A nationally representative study of maternal obesity in England, UK: trends in incidence and demographic inequalities in 619,323 births, 1989–2007. Int J Obes 2010;34:420–8. 5. World Health Organisation. Global Health Observatory Data Repository: infant mortality data by country. 2014. http://apps.who.int/gho/data/view.main.200? lang=en 6. Dodd JM, McPhee AJ, Turnbull D, et al. The effect of antenatal dietary and lifestyle advice for women who are overweight or obese on neonatal health outcomes: the LIMIT randomised trial. BMC Med 2014;12:163. 7. Briley AL, Barr S, Badger S, et al. A complex intervention to improve pregnancy outcome in obese women: the UPBEAT randomized controlled trial. BMC Pregnancy Childbirth 2014;14:74. 8. Chiswick CA, Reynolds RM, Denison FC, et al. Efficacy of metformin in pregnant obese women: a randomized controlled trial. BMJ Open 2015;5:e006854.
Evid Based Med Month 2015 | volume 0 | number 0 |
Copyright Article author (or their employer) 2015. Produced by BMJ Publishing Group Ltd under licence.
1
Cohort study
Maternal overweight and obesity in early pregnancy are associated with an increase in infant mortality risk 10.1136/ebmed-2014-110163
Rebecca M Reynolds Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, UK Correspondence to: Professor Rebecca Reynolds, Endocrinology Unit, University/BHF Centre for Cardiovascular Science, Queen’s Medical Research Institute, Edinburgh, EH16 4TJ, UK; [email protected]
Commentary on: Johansson S, Villamor E, Altman M, et al. Maternal overweight and obesity in early pregnancy and risk of infant mortality: a population based cohort study in Sweden. BMJ 2014;349:g6572.
with maternal overweight and obesity. Obesity grades II–III (BMI ≥35) was also associated with increased infant mortality due to congenital anomalies and sudden infant death syndrome.
Commentary This study demonstrates that maternal overweight, as well as maternal obesity is associated with increased infant mortality risk and the risk increases with increasing BMI.1 2 The excess mortality is explained by an increased mortality risk in term births, due to birth asphyxia and other neonatal morbidities, including congenital anomalies, and also by an increased prevalence of preterm births. This study adds to our knowledge of the adverse effects of maternal overweight and obesity in pregnancy on offspring outcomes3 and is of concern given the high prevalence of maternal overweight and obesity.4 Indeed Sweden has one of lowest rates of infant mortality in the world5 so outcomes may be worse in areas where antenatal care is not as good. The main strength of the study was the large, population-based approach with prospectively collected data and adjustments for several confounders including surrogates of socioeconomic status. The study raises the question of what we can do to improve outcomes. Ideally, overweight or obese women should be encouraged to lose weight before pregnancy, but this may be challenging to achieve. Information about gestational weight gain was not available in the study and this may be an area to target. Trials of lifestyle intervention during pregnancy6 7 or pharmacological interventions that limit gestational weight gain8 are ongoing and results are eagerly awaited.
Context Rates of overweight and obesity among women of childbearing age are increasing worldwide. This has implications for infant health as pregnancy complications, including preeclampsia and gestational diabetes, are more common in women with a higher body mass index (BMI) and there may be more indications for medical preterm delivery. Findings from studies testing associations between maternal BMI and infant mortality are inconsistent, with little information on specific causes of infant mortality. This study used a large nationwide cohort to test associations between maternal BMI and infant, neonatal and postneonatal mortality outcomes, including cause-specific mortality.
Implications for practice The study highlights the need for public health messages to emphasise the importance of a healthy weight for pregnancy. In addition, healthcare professionals should be alerted to the need for careful monitoring of overweight and obese women during pregnancy to ensure optimal outcome for mother and baby. Competing interests None. Provenance and peer review Commissioned; internally peer reviewed.
Methods This was a population-based cohort study including 1 857 822 live single births in Sweden from 1992 to 2010. Maternal BMI was calculated from self-reported height and weight measured at the first antenatal visit. Infant, neonatal and postneonatal mortality were defined as infant deaths during the first year of life, within and after the first 28 days of life, respectively. Overall mortality rates (deaths per 1000 liveborn infants) were calculated and stratified by gestational length and by specific causes of infant death according to International Classification of Diseases codes. ORs were adjusted for maternal age, parity, smoking, education, height, country of birth and year of delivery.
Findings Infant mortality rates increased from 2.4/1000 among normal weight women (BMI 18.5–24.9) to 5.8/1000 among women with grade III obesity (BMI ≥40). Compared with normal weight, overweight (BMI 25.0–29.9) and grade I obesity (BMI 30–34.9) were also associated with modestly increased risks of infant mortality (adjusted ORs 1.25 (95% CI 1.16 to 1.35) and 1.37 (95% CI 1.22 to 1.53)) with more than doubling the risk at higher BMI levels. In stratified analyses, maternal BMI was related to infant mortality primarily in term births (≥37 weeks) where risks of deaths due to birth asphyxia and other neonatal morbidities increased
References 1. Meehan S, Beck CR, Mair-Jenkins J, et al. Maternal obesity and infant mortality: a meta-analysis. Pediatrics 2014;133:863–71. 2. Aune D, Saugstad OD, Henriksen T, et al. Maternal body mass index and the risk of fetal death, stillbirth, and infant death: a systematic review and meta-analysis. JAMA 2014;311:1536–46. 3. Reynolds RM, Allan KM, Raja EA, et al. Maternal obesity during pregnancy and premature mortality from cardiovascular event in adult offspring: follow-up of 1,323,275 person years. BMJ 2013;347:f4539. 4. Heslehurst N, Rankin J, Wilkinson JR, et al. A nationally representative study of maternal obesity in England, UK: trends in incidence and demographic inequalities in 619,323 births, 1989–2007. Int J Obes 2010;34:420–8. 5. World Health Organisation. Global Health Observatory Data Repository: infant mortality data by country. 2014. http://apps.who.int/gho/data/view.main.200? lang=en 6. Dodd JM, McPhee AJ, Turnbull D, et al. The effect of antenatal dietary and lifestyle advice for women who are overweight or obese on neonatal health outcomes: the LIMIT randomised trial. BMC Med 2014;12:163. 7. Briley AL, Barr S, Badger S, et al. A complex intervention to improve pregnancy outcome in obese women: the UPBEAT randomized controlled trial. BMC Pregnancy Childbirth 2014;14:74. 8. Chiswick CA, Reynolds RM, Denison FC, et al. Efficacy of metformin in pregnant obese women: a randomized controlled trial. BMJ Open 2015;5:e006854.
Evid Based Med Month 2015 | volume 0 | number 0 |
Copyright Article author (or their employer) 2015. Produced by BMJ Publishing Group Ltd under licence.
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