A report into perinatal and maternal death shows there is further evidence of the link between smoking, obesity and stillbirths.
The Perinatal and Maternal Mortality Review Committee report, released on Tuesday, said the number of stillbirths was falling but that there was a clear link between stillbirth and smoking, and stillbirth and obesity.
It said it could be shown for the first time that smoking and obesity were independent risk factors, and that pregnant women must get as much help and support as possible to quit smoking and reach a healthy weight before and during pregnancy.
The report also showed the risk of maternal deaths was 2-1/2 times higher for women living in the most deprived areas, and that improving access to services remained a challenge.
The chair of the Perinatal and Maternal Mortality Review Committee, Sue Belgrave, said the appropriate messages needed to go out to pregnant women and their families.
"When I'm seeing a woman in an ante-natal clinic who is smoking and I'm talking to her about this, one of the barriers she brings up is that the rest of the family smokes. And so we need to give this message not only to the women who are pregnant or contemplating pregnancy but to their wider family and whanau"
The study also revealed Indian women are most at risk of stillbirths. Ms Belgrave said Indian women suffer maternal conditions such as hypertension and diabetes, but no one knows why they have more stillbirths than other women, and the findings are a flag to midwives to ensure the women are carefully monitored.