Pregnancy rates decrease and miscarriages increase when a father is over 35 years of age, a scientist will tell the 24th annual conference of the European Society of Human Reproduction and Embryology (Monday 7 July). Dr. Stephanie Belloc, of the Eylau Centre for Assisted Reproduction, Paris, France, will say that this is the first time that such a strong paternal effect on reproductive outcomes has been shown.
Dr. Belloc and colleagues followed up 21239 intrauterine inseminations (IUIs). In IUI 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. 12236 couples who had consulted at the Centre between January 2002 and December 2006 were involved, and the husband's semen was used in all cases. In most cases the couples were being treated because of the husband's infertility
The sperm of each partner was examined at the time of the IUI for a number of characteristics, including sperm count, motility and morphology. Clinical pregnancy, miscarriage and delivery rates were also carefully recorded. Detailed analysis of the results allowed the scientists to separate out the male and female factors related to each pregnancy.
Maternal age was closely associated with a decreased pregnancy rate of 8.9% in women over 35 years, compared to 14.5% 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," says Dr. Belloc. "And, perhaps more surprisingly, miscarriage rates increased where the father was over 35."
The effect of maternal age on the ability to conceive and on miscarriage rates is well known, but there is still controversy about the role of the father. Although there are many reports that show an overall decline in sperm counts and quality from decade to decade, up to now there has been no clinical proof that simply being an older man has a direct effect on a couple's fertility.