Researchers in France studying over 12,000 couples with fertility problems found that when the man was over 35 pregnancy rates fell and perhaps more surprisingly, miscarriage rates rose, leading them to conclude that the age of the father was just as important as the age of the mother in reaching a successful pregnancy.

The findings are being presented today, Monday 7th July, at the 24th annual conference of the European Society of Human Reproduction and Embryology (ESHRE) in Barcelona, Spain, by lead investigator Dr Stephanie Belloc, of the Eylau Centre for Assisted Reproduction in Paris, France.

This is the first time such a strong effect from the father on reproductive success rates has been found from research, said Belloc in a press statement.

Belloc and her team studied 12,236 couples who underwent 21,239 intrauterine inseminations (IUIs) at the Eylau Centre between January 2002 and December 2006 and used the male partner’s sperm (as opposed to donated sperm) in all cases. Most couples were being treated because of the man’s infertility.

In IUI, the sperm is spun in a centrifuge to remove the seminal fluid and then inserted directly into the uterus while the woman is ovulating. This technique is less invasive than IVF and is used when the woman’s fertility is not a problem.

If the sperm is not “washed” in the centrifuge to remove the seminal fluid, the prostaglandins in the seminal fluid can cause cramps in the uterus which expels the semen.

For each IUI, the sperm was examined for a number of characteristics, such as sperm count, motility (how agile they are) and morphology or shape, and the clinical pregnancy, miscarriage and delivery rates were noted. The researchers then analyzed the results, distinguishing between male and female factors in influencing outcomes for each IUI case.

The results showed that maternal age was closely linked to decreased pregnancy rate, which was 8.9 per cent in women over 35 compared to 14.5 per cent in younger women.

But the scientists also found that the father’s age was also important, not only on pregnancy rates, but perhaps more surprisingly, on the rate of miscarriage, with a pronounced negative effect once the father was over 35 years of age.

The effect of the mother’s age on conception and miscarriage rates is already well known to scientists, but the effect of the father has not been very clear; studies have shown that sperm count and quality declines as men get older, but until now there has been no clinical evidence of the impact of the age of the man on a couple’s ability to have a successful pregnancy.

As Belloc explained, it was a question that needed to be answered once and for all:

“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,” she said.

Speculating on the reasons why the age of the man should impact fertility, Belloc said a number of recent studies have shown a ink between IUI success and DNA damage, which is linked to the man’s age.

The researchers are hoping to gather more evidence as they add more couples to the study in the coming years.

Belloc said this research will yield important information for couples wanting to start a family, and the larger the pool of couples from which the evidence is drawn the more helpful the information will be.

The study is clinical evidence to support the notion that DNA damage in older men reflects in fertility, Belloc said:

“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.”

She said that perhaps this will support the recommendation that IVF or ICSI should be the preferred treatment when either of the partners is over 35. In IVF the outer membrane of the egg (the zona pellucida) appears to stop the entry of sperm with DNA damage, and in ICSI, the best quality sperm is selected out.

“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,” said Belloc.

A representative of the Eylau Centre also said on an interview with the BBC aired early this morning that the likely cause of the decrease in male fertility after 35 was DNA fragmentation. He said that DNA fragmentation was not unusual in male sperm and often this is repaired “by the woman”, but when it is too fragmented it is beyond repair, leading to pregnancy failure and miscarriage, he said.

Source: ESHRE press statement, BBC News.

Written by: Catharine Paddock, PhD