A new study has found a mother's weight gain between pregnancies increases the risk of stillbirth and infant death.
The Swedish study, published in the medical journal The Lancet today, showed the risk of infant mortality increased for healthy women who gained even moderate weight before their second pregnancy.
It also found mothers who gained excessive weight between their first and second pregnancies had about a 50 percent higher risk of a stillbirth.
Auckland University head of obstetrics and gynaecology Lesley McCowan said when applied to New Zealand, the risk goes up from 3 in 1000 women to 4.5 in 1000.
Dr Chris McKinlay, senior lecturer at the University of Auckland and neonatal paediatrician, said the new data could change how health professionals look at mothers' weight gain.
"A lot of our focus to date has been on the weight of women during pregnancy and achieving a healthy weight gain, but this really interesting new data suggests that actually what happens between pregnancies can affect infant outcomes throughout the first year of life.
The study revealed the increased risk could apply to women of a healthy weight who gained as little 6kg between pregnancies.
"We've been trying to tackle still births for sometime and things like cot deaths and concentration on healthy weight between pregnancies might be another target to bring down these rates."
Though the study established a link between the mother's weight and infant mortality risk, researchers did not know the reason.
"In our commentary on our study we've speculated several things, one of which is that [being] overweight has been associated with cot death and it may be that's one factor," said Dr McKinlay.
"The other is that we know that women who are a larger weight or have diabetes find it more difficult to breastfeed and we know that breastfeeding is protective.
He said women should not be too worried about the new findings.
"For each individual woman, its not a cause to panic. Overall our risk of stillbirth in New Zealand is about four per thousand, so very low for each individual woman, but over the population that's about 240 stillbirths a year that we'd like to prevent."