While age is key in a woman’s odds of conceiving, whether naturally or via assisted reproduction, there is no consistent evidence that a man’s age affects the chances of success with infertility treatment, a new research review finds.

In an analysis of 10 studies mostly conducted in the past decade, Israeli researchers found that most of the studies showed no clear relationship between men’s age and couples’ odds of success with in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI).

Both IVF and ICSI involve joining a woman’s egg and a man’s sperm in a lab dish, then - if fertilization is successful - transferring one or more embryos to the woman’s uterus. ICSI is typically used for male fertility problems, including a low sperm count or poor sperm quality. It involves isolating a single sperm and injecting it directly into the egg.

It’s known that women’s fertility declines after age 35, and drops sharply after about age 40. And the odds of having a baby through assisted reproduction show a similar decrease.

Men are capable of fathering a child even into their golden years. However, studies have indicated that they do have a biological clock of sorts. Sperm quality, research suggests, may decline after age 40, and so too may the chances of having a baby; one study, for example, found that when the man was older than 40, a couple’s risk of miscarriage was higher compared with couples in which the man was younger.

However, only a handful of studies have looked at the relationship between men’s age and fertility-treatment outcomes.

For the new review, reported in the journal Fertility and Sterility, Dr. Lena Dain and colleagues at Carmel Medical Center in Haifa, Israel, pulled together 10 international studies that have looked at the question. Each involved anywhere from about 200 to 2,000 couples who underwent fertility treatment.

Overall, the researchers found, most of the studies failed to find an association between men’s age and sperm quality, the odds of couples’ conceiving or the chances of ultimately having a baby.

However, one U.S. study of 221 couples did find a connection: among couples in which the man was age 35 or younger, the pregnancy rate was 53 percent, versus 35 percent among men ages 36 to 40. The pregnancy rate dipped as low as 13 percent among men older than 40.

There was a similar pattern when it came to birth rates. Among men age 35 or younger, the rate was 38 percent, compared with 17 percent among those ages 36 to 40, and 7 percent for men older than 40.

This one study alone is not enough to prove that older paternal age does impede fertility treatment. However, the researchers point out, it was the only one of the group that was “prospective” - meaning it followed treatment-seeking couples over time, rather than reviewing their records after they had undergone fertility treatment. In general, prospective studies yield stronger evidence.

So while there is currently “insufficient evidence” that a man’s age affects fertility-treatment success, the researchers write, more studies - particularly prospective ones - are needed.

Future studies should also try to have more uniform criteria for what they are investigating and reporting, according to Dain’s team. The 10 studies they reviewed varied widely in the specific fertility-treatment protocols, the standards they used for including or excluding couples from the analysis, and in how they defined “advanced paternal age.”

There is evidence that a man’s age may only have a negative effect on fertility after age 50, the researchers write. However, some of the studies in their review defined advanced age as roughly age 40 and up.

So more studies with better defined age groups are needed, the researchers write.

Understanding how men’s age affects fertility in general is becoming increasingly important, as more and more couples postpone pregnancy and as second marriages become more common, Dain and her colleagues note.

In the U.S., they write, birth rates to fathers between the ages of 35 and 54 rose nearly 30 percent between 1980 and 2000 - from 68 per 1,000 men to 88 per 1,000.

SOURCE: Fertility and Sterility , online October 7, 2010.