Inter-pregnancy Weight Change and Risks of Severe Birth-Asphyxia-Related Outcomes in Singleton Infants Born at Term: A Nationwide Swedish Cohort Study

<div><p>Background</p><p>Maternal overweight and obesity are associated with increased risks of birth-asphyxia-related outcomes, but the mechanisms are unclear. If a change of exposure (i.e., maternal body mass index [BMI]) over time influences risks, this would be consistent with a causal relationship between maternal BMI and offspring risks. Our objective was to investigate associations between changes in maternal BMI between consecutive pregnancies and risks of birth-asphyxia-related outcomes in the second offspring born at term.</p><p>Methods and Findings</p><p>This study was a prospective population-based cohort study that included 526,435 second-born term (≥37 wk) infants of mothers with two consecutive live singleton term births in Sweden between January 1992 and December 2012.</p><p>We estimated associations between the difference in maternal BMI between the first and second pregnancy and risks of low Apgar score (0–6) at 5 min, neonatal seizures, and meconium aspiration in the second-born offspring. Odds ratios (ORs) were adjusted for BMI at first pregnancy, maternal height, maternal age at second delivery, smoking, education, mother´s country of birth, inter-pregnancy interval, and year of second delivery. Analyses were also stratified by BMI (<25 versus ≥25 kg/m²) in the first pregnancy.</p><p>Risks of low Apgar score, neonatal seizures, and meconium aspiration increased with inter-pregnancy weight gain. Compared with offspring of mothers with stable weight (BMI change of −1 to <1 kg/m²), the adjusted OR for a low Apgar score in the offspring of mothers with a BMI change of 4 kg/m² or more was 1.33 (95% CI 1.12–1.58). The corresponding risks for neonatal seizures and meconium aspiration were 1.42 (95% CI 1.00–2.02) and 1.78 (95% CI 1.19–2.68), respectively. The increased risk of neonatal seizures related to weight gain appeared to be restricted to mothers with BMI < 25 kg/m² in the first pregnancy. A study limitation was the lack of data on the effects of obstetric interventions and neonatal resuscitation efforts.</p><p>Conclusions</p><p>Risks of birth-asphyxia-related outcomes increased with maternal weight gain between pregnancies. Preventing weight gain before and in between pregnancies may improve neonatal health.</p></div

Maternal inter-pregnancy weight change and risks of low Apgar score (0–6) at 5 min, neonatal seizures, and meconium aspiration: live singleton second term infants of women in Sweden 1992–2012.

<p>Maternal inter-pregnancy weight change and risks of low Apgar score (0–6) at 5 min, neonatal seizures, and meconium aspiration: live singleton second term infants of women in Sweden 1992–2012.</p

Maternal characteristics and rates of low Apgar scores (0–6), meconium aspiration, and neonatal seizures: live-born singleton second term infants of women in Sweden 1992–2012.

<p>Maternal characteristics and rates of low Apgar scores (0–6), meconium aspiration, and neonatal seizures: live-born singleton second term infants of women in Sweden 1992–2012.</p

Maternal body-mass index and odds ratios for low Apgar scores at 5 and 10 minutes: live singleton term births in Sweden 1992–2010.

<p>In addition to regression models used in <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001648#pmed-1001648-t003" target="_blank">Table 3</a>, odds ratios are further adjusted for mode of delivery.</p

Maternal characteristics and rates of low Apgar scores at 5 and 10 minutes in live singleton term births in Sweden 1992–2010.

<p>Maternal characteristics and rates of low Apgar scores at 5 and 10 minutes in live singleton term births in Sweden 1992–2010.</p

Maternal body-mass index and odds ratios for meconium aspiration and neonatal seizures; live singleton term births in Sweden 1992–2010.

<p>In addition to regression models used in <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001648#pmed-1001648-t003" target="_blank">Table 3</a>, odds ratios are further adjusted for mode of delivery.</p

Month of Birth and Mortality in Sweden: A Nation-Wide Population-Based Cohort Study

<div><h3>Background</h3><p>Month of birth – an indicator for a variety of prenatal and early postnatal exposures – has been associated with life expectancy in adulthood. On the northern hemisphere, people born in the autumn live longer than those born during the spring. Only one study has followed a population longitudinally and no study has investigated the relation between month of birth and mortality risk below 50 years.</p> <h3>Methods and results</h3><p>In this nation-wide Swedish study, we included 6,194,745 subjects, using data from population-based health and administrative registries. The relation between month of birth (January – December) and mortality risk was assessed by fitting Cox proportional hazard regression models using attained age as the underlying time scale. Analyses were made for ages >30, >30 to 50, >50 to 80 and >80 years. Month of birth was a significant predictor of mortality in the age-spans >30, >50 to 80, and >80 years. In models adjusted for gender and education for ages >30 and >50 to 80 years, the lowest mortality was seen for people born in November and the highest mortality in those born in the spring/summer, peaking in May for mortality >30 years (25‰ excess hazard ratio compared to November, [95% confidence interval = 16–34 ]) and in April for mortality >50 to 80 years (42‰ excess hazard ratio compared to November, [95% confidence interval = 30–55]). In the ages >80 years the pattern was similar but the differences in mortality between birth months were smaller. For mortality within the age-span >30 to 50 years, results were inconclusive.</p> <h3>Conclusion</h3><p>Month of birth is associated to risk of mortality in ages above 50 years in Sweden. Further studies should aim at clarifying the mechanisms behind this association.</p> </div

Number of deaths and excess hazard ratio (EHR) in ‰ compared to November (95% confidence interval) in the age-span >30: crude model, adjusted for sex and education, male (adjusted for education) and female (adjusted for education) and with p-value for type 3-test.

<p>Number of deaths and excess hazard ratio (EHR) in ‰ compared to November (95% confidence interval) in the age-span >30: crude model, adjusted for sex and education, male (adjusted for education) and female (adjusted for education) and with p-value for type 3-test.</p

Number of deaths and excess hazard ratio (EHR) in ‰ compared to November (95% confidence interval) in the age-spans >30 to 50, >50 to 80 and >80 years: crude models and adjusted for sex and education with p-value for type 3-test.

<p>Number of deaths and excess hazard ratio (EHR) in ‰ compared to November (95% confidence interval) in the age-spans >30 to 50, >50 to 80 and >80 years: crude models and adjusted for sex and education with p-value for type 3-test.</p

Number of subjects and proportion of the population that died during the study time by age-span, sex and education group.

<p>Number of subjects and proportion of the population that died during the study time by age-span, sex and education group.</p