title: High Maternal Body Mass Index in Early Pregnancy and Risks of Stillbirth and Infant Mortality-A Population-Based Sibling Study in Sweden.
abstract: In a population-based case-control study, we investigated whether familial confounding influenced the associations between maternal overweight/obesity and risks of stillbirth and infant mortality by including both population and sister controls. Using nationwide data from the Swedish Medical Birth Register (1992-2011), we included all primiparous women with singleton births who also had a sister with a first birth during that time period. We used logistic regression analyses to calculate odds ratios (and 95% confidence intervals) adjusted for maternal age, height, smoking habits, education, and time period (5-year groups) of child's birth. Body mass index (BMI) was calculated as weight (kg)/height (m)(2) Compared with population controls with a normal BMI (18.5-24.9), stillbirth risk increased with increasing BMI (BMI 25-29.9: odds ratio (OR) = 1.51 (95% confidence interval (CI): 1.21, 1.89); BMI 30-34.9: OR = 1.77 (95% CI: 1.24, 2.50); BMI ≥35: OR = 3.16 (95% CI: 2.10, 4.76)). The sister case-control analyses revealed similar results. Offspring of obese women (BMI ≥30) had an increased risk of infant mortality when population controls were used (OR = 2.41, 95% CI: 1.83, 3.16), and an even higher risk was obtained when sister controls were used (OR = 4.04, 95% CI: 2.25, 7.25). We conclude that obesity in early pregnancy is associated with increased risks of stillbirth and infant mortality independently of genetic and early environmental risk factors shared within families.
authors.forename: Anna
authors.initials: A
authors.lastname: Lindam
authors.forename: Stefan
authors.initials: S
authors.lastname: Johansson
authors.forename: Olof
authors.initials: O
authors.lastname: Stephansson
authors.forename: Anna-Karin
authors.initials: AK
authors.lastname: Wikström
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
mesh_terms: D000328:Adult; D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D008423:Maternal Age; D000068097:Maternal Health / Q000706:statistics & numerical data / Q000639:trends; D009765:Obesity / Q000150:complications / Q000453:epidemiology*; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology; D035781:Siblings; D050497:Stillbirth / Q000453:epidemiology*; D013548:Sweden / Q000453:epidemiology; D015430:Weight Gain / Q000502:physiology; D055815:Young Adult
keywords: body mass index; familial confounding; infant mortality; neonatal mortality; postneonatal mortality; sibling-design studies; stillbirth