Washington, July 7 : A French scientist claims that she has, for the first time, found a strong paternal effect on reproductive outcomes in a study.
Dr. Stephanie Belloc of the Eylau Centre for Assisted Reproduction in Paris has discovered that pregnancy rates decrease, and miscarriages increase when a father is over 35 years of age.
During the study, Belloc and her colleagues followed up 21239 intrauterine inseminations (IUIs)-a process in which the sperm is 'washed', or spun in a centrifuge, in order to separate them from the seminal fluid, and then inserted directly into the uterus.
If the sperm are not washed they can cause uterine cramps which can expel the semen because of prostaglandins in the seminal fluid, the researcher points out.
Belloc revealed that 12236 couples, who had consulted at the Centre between January 2002 and December 2006, were involved in the study, and that the husband's semen was used in all cases.
She said that the couples were being treated in most cases because of the husband's infertility.
The researchers examined the sperm of each partner at the time of the IUI for a number of characteristics, including sperm count, motility and morphology. They also recorded clinical pregnancy, miscarriage, and delivery rates carefully.
An analysis of the data enabled the researcher to separate out the male and female factors related to each pregnancy.
It was found that maternal age was closely associated with a decreased pregnancy rate of 8.9 per cent in women over 35 years, compared to 14.5 per cent in younger women. Miscarriage rates were also typically affected by maternal age.
"But we also found that that the age of the father was important in pregnancy rates - men over 35 had a negative effect. And, perhaps more surprisingly, miscarriage rates increased where the father was over 35," says Dr. Belloc.
While it is well known that maternal age affects the ability to conceive as well as miscarriage rates, there is still controversy about the role of the father.
Many reports have shown an overall decline in sperm counts and quality from decade to decade, but still there exists no clinical proof that simply being an older man has a direct effect on a couple's fertility.
"We already believed that couples where the man was older took longer to conceive, but a number of reasons had been put forward for this. Neither was there any definite evidence that miscarriage rates increased when the man was older.
To undertake a complex multivariant statistical analysis of data from a large roup of patients was difficult, but we thought it was a question that needed to be answered once and for all.
Some recent studies have established a relationship between the results of IUI and DNA damage, which is also correlated to a man's age, suggesting that it might be an important factor, but until now there was no clinical proof," says Dr. Belloc.
She revealed that further studies, to be conducted in the next few years to confirm their results, would include more couples.
"This research has important implications for couples wanting to start a family, and we need to research it in as large a group as possible," she says.
"How DNA damage in older men translates into clinical practice has not been shown up to now. Our research proves for the first time that there is a strong paternal age-related effect on IUI outcomes, and this information should be considered by both doctors and patients in assisted reproduction programmes.
"We believe that the use of IVF or ICSI should be suggested to infertile patients where either party is over 35 years of age.
In IVF, the zona pellucida (the outer membrane of the egg) seems to be an efficient barrier in preventing the penetration of sperm with DNA damage, and in ICSI, the best sperm can be selected out for use.
These methods, although not in themselves a guarantee of success, may help couples where the man is older to achieve a pregnancy more quickly, and also reduce the risk of miscarriage," she adds.
A presentation on the study was made at the 24th annual conference of the European Society of Human Reproduction and Embryology on Monday.