Washington D.C. [US], Oct. 17 : Babies born to women in the age of 40 and over from assisted reproduction have fewer birth defects compared with those from women, who conceive naturally at the same age, suggests a new research.

This is contrary to the widespread belief that greater risk of birth defects after assisted conception is due to the frequent use of these services by older women.

The researchers believe this could point to the presence of more favorable biological conditions in IVF (in vitro fertilization) specific to pregnancies in older women but they're currently working to determine the exact cause.

The research is based on the data of all live births recorded in South Australia from 1986-2002.

These include more than 3,01,000 naturally conceived births as well as 2,200 births from IVF and almost 1,400 from ICSI (intracytoplasmic sperm injection).

The average prevalence of a birth defect was 5.7 percent among naturally conceived births, 7.1 percent for the IVF births and 9.9 percent for the ICSI births across all age groups.

In births from assisted reproduction, the prevalence of birth defects ranged from 11.3 percent at its highest for women less than 30 years of age using ICSI, down to 3.6 percent for women aged 40 and older using IVF.

For natural conceptions, the corresponding prevalence across age groups was 5.6 percent in young women, increasing to 8.2 percent in the women aged above 40.

"There's something quite remarkable occurring with women over the age of 40 who use assisted reproduction," said lead author Michael Davies.

"We know from our previous studies that women who undergo assisted reproduction have an increased rate of birth defects compared to women who conceive naturally. We also know that among women who conceive naturally, the rate of birth defects increases exponentially from age 35 onwards. Therefore, it was widely assumed, but untested, that maternal age would be a key factor in birth defects from assisted reproduction," he further said.

Adding, "However, our findings challenge that assertion. They show that infertile women aged 40 and over who used assisted reproduction had less than half the rate of birth defects of fertile women of the same age, while younger women appear to be at an elevated risk."

For women treated with IVF and ICSI combined the greatest age-related risk of birth defects was among the young women at or around 29 years of age.

"With a prevalence of 9.4 percent, their risk was more than double the rate of 3.6 percent observed for the patients aged over 40 and significantly higher than for fertile women of the same age, at 5.6 percent," Davies said.

These results could have broader implications for infertility treatment if researchers can understand why older women do better on assisted reproduction.

"There is some aspect of IVF treatment in particular that could be helping older women to redress the maternal age issues we see among natural conception, where we observe a transition at around the age of 35 years toward a steadily increasing risk of birth defects. We don't know what that is quite yet - it could be an aspect of hormonal stimulation that helps to reverse the age-related decline in control of ovulation," he concluded.

The research was published in BJOG: An International Journal of Obstetrics & Gynaecology (BJOG). (ANI)