Though assisted-reproduction techniques (ART) are known to come with a higher risk for birth defects, a new review of defect rates in Western Australia shows major birth defects becoming less common over the course of a decade among babies born through ART.
It's unclear why there have been fewer birth defects in more recent years.
"Changes to clinical practice may be largely responsible with improved (laboratory techniques) leading to the transfer of 'healthier' embryos," suggested Michele Hansen, the lead author of the study and a researcher at the Telethon Institute for Child Health Research in Subiaco, Western Australia.
It's also not known why babies conceived through ART are likelier to have an increased risk of birth defects in the first place.
A recent estimate, based on the results of several dozen studies, found that ART is linked with a 37 percent increase in the risk of being born with a birth defect (see Reuters Health story of April 19, 2012).
Hansen said she and her colleagues wanted to get an update on those rates using a database of all births in Western Australia.
They collected information on more than 207,000 births, including babies conceived through two common techniques, 1,328 by in vitro fertilization and 633 by intracytoplasmic sperm injection, from 1994 to 2002.
The data also included pregnancies terminated due to a defect in the fetus.
Overall, major birth defects, including cleft lip, hip dysplasia and malformations of the heart, abdominal wall and genitals, affected about eight percent of singleton babies conceived by ART, compared to about five percent of babies conceived without assistance.
When the researchers compared the period between 1994 and 1998 to the years between 1998 and 2002, they saw a decline in birth defects over time among babies whose parents used ART.
In the first period, nearly 11 percent of ART babies had a birth defect diagnosed by age six, compared to about 7.5 percent in the second period.
In the journal Obstetrics & Gynecology, Hansen calls the results "encouraging," though she can't explain them.
The researchers speculate they could stem from a combination of ART techniques becoming available to a wider swath of the population, and changes in how the techniques themselves are applied.
"It is very difficult to assess the impact of each of these changes on birth defect risk, however, we believe that changes to laboratory practice...changes to the medications used for ovarian stimulation requiring lower doses and shorter stimulation periods; together with a decrease in the number of embryos transferred may all have had a positive impact on the 'health' of embryos transferred in ART treatments," she told Reuters Health in an email.
"Whilst our study does still show that babies born using Assisted Reproductive Technology remain at a higher risk of birth defects, couples seeking ART treatment can be reassured that the vast majority of ART infants are born healthy and do not have a birth defect," said Hansen.