Even if they are of a healthy weight during their first pregnancy, women who gain weight between pregnancies face an increased risk of death for their second child.
The study was led by Prof. Sven Cnattingius, of Karolinska Institutet in Stockholm, Sweden, and is published in The Lancet.
According to the American College of Obstetricians and Gynecologists (ACOG), the population demographics of pregnant women have changed significantly over the past 10 years or so, and more women are overweight or obese at conception.
This can affect both the health of a woman and her baby; there are links between excessive weight gain in pregnancy and increased birth weight and postpartum weight retention.
On the flip side, there are links between inadequate weight gain and decreased birth weight, so gaining the right amount of weight during pregnancy is key.
According to the Mayo Clinic in Rochester, MN, how much weight a pregnant woman gains depends on various factors, including pre-pregnancy weight and body mass index (BMI).
Recommended weight gains during pregnancy are as follows:
- Underweight (BMI less than 18.5): should gain 28-40 lbs during pregnancy
- Normal weight (BMI 18.5-24.9): should gain 25-35 lbs
- Overweight (BMI 25-29.9): should gain 15-25 lbs
- Obese (BMI 30 or more): should gain 11-20 lbs.
Women who are carrying twins or other multiples, however, will likely need to gain more weight.
Stillbirth risks increase with increased maternal weight gain
To conduct their latest study, the researchers used data from the Swedish Medical Birth Register, which assessed over 450,000 women who gave birth to their first and second child between 1992-2012.
The team analyzed risk of stillbirth - which is defined as fetal death at 28 weeks or later - and infant mortality - defined as death within the first year of life - and compared it with a change in the mother's BMI between the two pregnancies.
Results show that babies of mothers who gained more than 4 BMI units - which is around 24 lbs in Swedish women of an average height - between the two pregnancies had a 50% higher risk of dying in the first 4 weeks of life, compared with babies of women who had a more stable weight.
The researchers say these results remained, even after adjusting for maternal age, education level and smoking - all of which are known to affect stillbirth risk.
Causes of death for the infants included congenital abnormalities, birth asphyxia, infections and sudden infant death syndrome (SIDS).
Furthermore, stillbirth risks rose with increasing weight gain; even mothers who had a normal BMI during their first pregnancy had increased infant mortality risks with increased weight gain.
In detail, infant death risk was 27% greater for women who gained between 13-24 lbs, and 60% greater for mothers who gained more than 24 lbs, compared with mothers of a stable weight.
Maternal weight loss decreases infant death likelihood
Based on their results, the researchers say increments in BMI in women of a healthy weight may demonstrate a greater fat mass increase than in obese women and may, therefore, pose a greater risk.
Interestingly, overweight mothers who lost at least 13 lbs before their second pregnancy saw a 50% decreased likelihood of infant death.
"The public health implications are profound," says Prof. Cnattingius of their results. He adds:
"Around a fifth of women in our study gained enough weight between pregnancies to increase the 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."
Study co-author Prof. Eduardo Villamor, from the University of Michigan School of Public Health in Ann Arbor, adds that "overweight and obesity in pregnant women has reached epidemic levels. More than half of women in the USA and 1 in 3 women in Sweden are either overweight or obese at the start of their pregnancy."
He adds that their 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."
Medical News Today recently reported on a study that showed infant deaths are on the rise due to the use of crib bumpers.