Published: 2014-12-03 09:35 | Updated: 2014-12-03 09:35

Increased infant mortality rates among children of overweight women

Children face a greater risk of dying during the first year of life if the mother is overweight. This is the conclusion drawn by a new study from Karolinska Institutet published in the scientific periodical BMJ.

In Sweden, around 3 in 1,000 children die during their first year. In a global context, this is one of the lowest infant mortality rates, but there are still ways to reduce infant mortality further, even in Sweden. One risk factor that should be preventable is overweight and obesity among young women.

"Our research shows that risk in children increase as their mothers become increasingly overweight”, says Stefan Johansson, senior consultant at the Sachs' Children's Hospital in Stockholm, and researcher at Karolinska Institutet. “For an individual woman, regardless of her weight, the risk of her child dying is very small. However, our results are still important from a population perspective, as overweight is common among women of a childbearing age.”

Over 1 million women

The study is based on data from the Swedish Medical Birth Register and encompasses over 1 million women and their 1.8 million children born in the period 1992–2010. When analysing this extensive set of data, the researchers investigated whether the mothers' body mass index (BMI) in early pregnancy was associated with the risk of the infant death. Of all the women, 24 per cent were overweight (BMI 25.0–29.9) and 9 per cent were obese (BMI 30.0 and up).

An increasing BMI was associated with an increasing rate of infant mortality; from 2.4 cases per 1,000 women of normal weight (BMI 18.5–24.9) to 5.8 cases per 1,000 women with the most pronounced obesity (BMI 40.0 and above). Relatively speaking, the increase in risk was moderate for children of overweight women (BMI 25.0–29.9) or mild obesity (BMI 30.0–34.9), at 25 and 37 per cent respectively. In women with more pronounced obesity (BMI 35.0 and up), the child's relative risk was doubled.

In two previous projects, the research group have found that increasing BMI in women increases the risk of premature births and hypoxia during birth; two complications that can lead to the child's death.

"However, when we looked at the causes of infant deaths, we realised that there were several different underlying problems,” says Stefan Johansson. “Other than premature birth and hypoxia, congenital abnormalities and diseases during the neonatal period also contributed to the higher mortality rate.”

Promote public health

The researchers hope their results do not worry women with a high BMI, as it is still rare for infants to die in Sweden. The most important message of this study, according to Stefan Johansson, is the importance of broad-based strategies to promote public health. A healthier society with a population being more normal weight would also be beneficial to the health of newborns.

"Another important message relates to antenatal and neonatal care. Deliveries involving overweight women, and especially those with a significantly elevated BMI, should be considered to carry a higher risk”, says Stefan Johansson. “The health service has a responsibility to be particularly observant in these cases, to minimise risks to both mother and child.”

Financial support for the study was provided by an unrestricted grant from Karolinska Institutet (Distinguished Professor Award to Professor Sven Cnattingius), and from the Swedish Research Council for Health, Working Life and Welfare.

Publication

Maternal overweight and obesity in early pregnancy and risk of infant mortality – a population-based cohort study in Sweden
Stefan Johansson, Eduardo Villamor, Maria Altman, Anna-Karin Edstedt Bonamy, Fredrik Granath, Sven Cnattingius
British Medical Journal (BMJ) 2014;349:g6572, online 2 December 2014