The new study from from Aarhus University Hospital in Denmark also indicates higher stillbirth risks for those who undergo intracytoplasmic sperm injection, although researchers point out the risk from both IVF and ISI still is low.
"The results from our study emphasize the need for continuous follow-up of the outcome of fertility treatments so that the information given to infertile couples seeking treatment can be differentiated to their individual circumstances," Kirsten Wisborg, who led the study, wrote in the journal Human Reproduction .
The new study , which involved 20,000 pregnancies from August 1989 to October 2006, also indicates that the higher risk may be the result of fertilization treatments, rather than infertility itself. That's because the risks of those who conceived after more than a year of trying (called subfertile) were almost similar to those of couples who conceived within a year of first trying.
"This may indicate that the increased risk of stillbirth is not explained by infertility and may be due to other, as yet unexplained factors, such as the technology involved in IVF and ICSI or some physiological difference in the couples that require (it)," Wisborg wrote.
The rate of stillbirth after IVF/ICSI was 16.2 per thousand, compared to 3.7 per thousand in fertile couples who conceived without medical help.