Women who put on weight after their first pregnancy are more likely to have a stillborn second child or a baby who dies within the year than those whose weight remains stable, new research shows.
A study carried out in Sweden confirms that the increased risk of the baby’s death in the womb or within its first year of life is real in women who put on even a modest amount of weight – about 6kg (13lb) – between pregnancies. It affects all women, not just those who are overweight or obese when they get pregnant for the first time.
“The public health implications are profound,” said the study’s co-author Prof Sven Cnattingius from the Karolinska Institutet in Stockholm. “Around a fifth of women in our study gained enough weight between pregnancies to increase their risk of stillbirth by 30–50%, and their likelihood of giving birth to babies who die in infancy increased by 27–60%, if they had a healthy weight during their first pregnancy.”
Because infant death and stillbirth are relatively rare, the increased risk does not equate to large numbers of deaths. In England and Wales, nearly five babies were stillborn for every 1,000 live births in 2013, according to the Office for National Statistics, and infant mortality in the UK was 3.8 per 1,000 live births in 2014. Among women who have put on significant weight – a rise in their body mass index (BMI) of 4 points or about 11kg in an average-height Swedish woman – there would be about two more stillbirths and the same number of extra deaths per 1,000 births.
But experts say stillbirths and infant deaths are already unacceptably high and that it is important to look for ways to help women who become pregnant keep their weight down.
“The prevalence of overweight and obesity in pregnant women has reached epidemic levels,” said Eduardo Villamor, a professor of epidemiology at the University of Michigan school of public health in the US and co-author of the paper published by the Lancet medical journal.
“More than half of women in the USA and one in three women in Sweden are either overweight or obese at the start of their pregnancy. Our findings highlight the importance of educating women about maintaining a healthy weight during pregnancy and reducing excess weight before becoming pregnant as a way to improve infant survival.”
The study was carried out using the Swedish medical birth register. The scientists had data on more than 450,000 women who gave birth to a first and second child between 1992 and 2012, including their BMI and details of any stillbirth or infant death.
The causes of such deaths included congenital abnormalities, birth asphyxia, infections and sudden infant death syndrome. The researchers were able to allow for other factors that make stillbirth or infant death more likely, such as smoking and the mother’s age.
Women who lost weight between the first and second birth were at lower risk of having a stillbirth or infant death. The authors say that “prevention of weight gain and promotion of weight loss in overweight women might reduce stillbirth and infant mortality” in women having a second or subsequent child.
Why weight gain affects the baby is not completely clear, they say. Women who are overweight have more fat tissue, which can cause raised blood pressure, which is a risk to the baby in the womb. They are more likely to suffer from gestational diabetes – a form of the condition that is particular to pregnancy – which can increase the chances of heart defects in the baby, said Andrew Whitelaw, an emeritus professor of neonatal medicine at the University of Bristol.
“Excessive fat tissue increases the risk of critical oxygen deprivation during labour and also increases inflammation, and that could trigger preterm birth which certainly increases mortality,” he said. “Treatment programs to reduce weight gain between pregnancies have proved difficult in the past but are clearly needed.”
He called for a larger study even than that carried out in Sweden, using data across the NHS to find out the causes.
