Women who find it difficult to become pregnant are more likely to have a stillbirth or a baby who dies within a month of birth, according to Australian research.
And the risks of serious complications are greater in those women who end up conceiving without using invasive medical treatments such as in-vitro fertilisation.
A University of Adelaide study, the most detailed of its kind in the world, compared the outcomes from 300,000 births in South Australia over 17 years.
The study included 4300 babies born from assisted reproductive therapies.
Researchers found babies conceived by IVF had at least double the risk of serious complications such as stillbirth, preterm birth, very low birth weight and newborn death compared with naturally conceived babies.
Professor Michael Davies, from the university's Robinson Institute, said the study confirmed previous studies that linked IVF to adverse outcomes for babies.
But in a first, the study also looked at women with known fertility problems who did not have IVF and found that they had even more birth-related complications.
This raised the possibility that lifestyle issues such as obesity might be contributing as well.
"This may be due to the underlying medical conditions related to their infertility, or the use of fertility medications or therapies that are not recorded," Professor Davies said.
That included the possible negative effects of low-key fertility treatments such as clomiphene citrate, a drug used to trigger ovulation. "There is something going on in that group of women that is a real priority for future research, because the worst outcomes are occurring in the group of people who have the least invasive treatment," he said.
University of WA professor of reproductive medicine Roger Hart said though it was well established that children born from IVF had significantly worse birth-related outcomes, fertility practices had improved since the study, which tracked births from 1986 to 2002.
"It is unclear as to the cause of the adverse outcomes. However, as this study confirms, women with a degree of subfertility have an adverse perinatal outcome even if they do not ultimately need IVF," he said.
Professor Hart said the health of the mother at the time of becoming pregnant was likely to have a significant effect on her child's longer term health.