Maternal Obesity Linked To Increase Infant Mortality

Stefan Johansson, MD PhD consultant neonatologist Stockholm, Interview with:
Stefan Johansson, MD PhD
consultant neonatologist
Stockholm, Sweden

Medical Research: What is the background for this study?

Dr. Johansson: Maternal obesity (BMI ≥ 30) has previously been linked to increased infant mortality. However, research has not produced consistent results. For example, there are disagreements whether infants to overweight mothers (BMI 25-29) are at increased risk, and research on BMI-related specific causes of death is scarce.

Medical Research: What are the main findings?

Dr. Johansson: Within the whole Swedish population of women delivering singleton infants during 1992-2010, we investigated whether maternal BMI in early pregnancy was associated with infant mortality. The cohort included 1.1 million women and 1.8 million infants. Of included women, 24% were overweight and 9% were obese.

Infant mortality rates consistently increased with increasing maternal BMI, from 2.4 per 1000 among normal-weight women to 5.8 per 1000 among the most severe obese women. In regression models, adjusted for maternal age, parity, smoking, education, height, country of birth and year of delivery, we found modest but significantly increased risks for overweight and mildly obese women. Adjusted odds ratios (95% confidence intervals) for BMIs of 25-29 and 30-34 were 1.25 (1.16-1.35) and 1.37 (1.22-1.53), respectively. More severe obesity was associated with higher risks. Corresponding odds ratios for BMIs of 35-39 and ≥40 were 2.11 (1.79-2.49) and 2.44 (1.88-3.17).

The BMI-related increased infant mortality risks were related to preterm birth, congenital malformations, birth asphyxia and other neonatal morbidities.

We also estimated the number of infant deaths attributed to maternal overweight and obesity by calculating the population attributable fraction (PAF). Given a causal relation, we estimated that 11% of the infant mortality in Sweden could be attributed to maternal BMI ≥25.

Medical Research: What should clinicians and patients take away from your report?

Dr. Johansson: Although all women (and men) should aim for healthy lifestyles, our research carries little meaning to an individual woman. After all, the probability of an infant death to any woman, normal-weight or obese, is very small.

For clinicians, our findings are more relevant. Antenatal care services and delivery units should give extra caution to overweight and obese women, to minimize risks for the mother and infant.

Most importantly, our study adds to the big picture everyone is already aware of, showing that overweight and obesity carries health risks. As over-weight and obesity is so prevalent, our results are important for population-level. Broad public health efforts should continue to promote healthy lifestyles, as a more normal-weight population would gain infant health.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Johansson: This study is based on Swedish women and therefore we believe that similar studies of the same size should be carried out in other countries. We would also like see more research on the pathways behind the associations we found. Finally, it is time to do intervention studies designed to reduce risks for pregnancy and obstetric complications for overweight and obese women.



Maternal Overweight and Obesity and Risks of Severe Birth-Asphyxia-Related Complications in Term Infants: A Population-Based Cohort Study in Sweden

Martina Persson, Stefan Johansson,Eduardo Villamor,Sven Cnattingius 

Published: May 20, 2014 DOI: 10.1371/journal.pmed.1001648


Maternal obesity and risk of preterm delivery.