Published: 03-12-2015 08:00 | Updated: 03-12-2015 10:31

Weight gain between pregnancies may influence baby’s survival

A novel study from Karolinska Institutet and University of Michigan in the U.S. shows that gaining weight from one pregnancy to the next can increase the risk that women will face stillbirth or lose their second babies within the first year of life. The findings are being published in The Lancet and build on data from more than 450,000 women in Sweden.

“These tragic events are still very rare among infants of mothers with high weight gain. However, as many women gain weight between pregnancies, our results are very important from a public health perspective”, says principal investigator Sven Cnattingius, professor of reproductive epidemiology at Karolinska Institutet.

In their study, researchers reviewed data from the first two pregnancies of nearly 457,000 women who gave birth in Sweden from 1992 to 2012. The women’s information was recorded in the Swedish Medical Birth Register, which since 1973 has collected information on about 98 percent of all births in that country. Weight was assessed at the beginning of each pregnancy. The results show that stillbirth risk rose with larger gains in body mass index (BMI) from first to second pregnancy. Compared with women who kept their weight, women whose BMI increased more than four units had a 50 percent increased risk of stillbirth.

Among women of normal weight in first pregnancy, high weight gain also increased the risk of infant mortality: when their BMI increased by 4 units or more, risk of infant mortality increased by 60 percent. On the other hand, the results also point to the opposite situation. Women who were overweight by their first pregnancy, defined as a BMI of 25 or more (corresponding to at least 70 kg of women with average height), but who lost weight before the second pregnancy, reduced their risk of infant mortality.

Rare events in Sweden

Every fifth women in the study material gained so much weight that it influenced risks of stillbirth and infant mortality (i.e. at least 2 BMI units, corresponding to 5.5 kg). However, the researchers point out that stillbirth and infant mortality are very rare events in Sweden, and only 2.4 per 1000 births resulted in a stillbirth and 2.1/1000 in infant mortality. There are annually around 100,000 births in Sweden.

“Previously, we have published that risks of stillbirth, infant mortality and morbidity increase with maternal weight, and in this new study we find that find that weight gain influence mortality risks. Taken together, our results support the conclusion that mother’s weight per see may influence infant chances of survival”, says Dr Cnattingius. “Still, the explanation for the findings is still speculative. We cannot differentiate from the data whether it is the weight gain during the pregnancy or in between pregnancies that is of significance”.

Financial support was provided by the Swedish Research Council for Health, Working Life and Welfare, and a Karolinska Institutet Distinguished Professor Award to Sven Cnattingius.