Advancing age in men directly affects their ability to become fathers, with a relationship similar to women’s age and likelihood of becoming pregnant. Because men do not go through a visible decline in their fertility (like menopause in women), the age of the partner has until now been considered a major factor in any couple’s chances of conceiving, whether through natural conception or IVF. New research on in vitro fertilization from Harvard Medical School reveals that the likelihood of normal fertilization, pregnancy and birth is directly related to the age of the father. The study is based on the analyzed data from 19,000 in vitro procedures performed with a total of 7,753 couples. The couples were divided into age groups: under 30, 30-35 years old, 35-40 years old and 40-42 years old. As expected, the success rate in conception and birth was lowest in the group with women between 40-42 years of age. They required at least 6 in vitro procedures and the effect of the woman’s age was clearly distinguishable. The scientists were surprised, however, when they discovered a new dependence: in all other age groups, the success rate of the procedures decreased as the man’s age increased. NEWS_MORE_BOX According to the research data, in a couple with a woman under 30 and a man between 40-42 years of age, the success rate was 46%. In a couple with a woman under 30 and a man between 30 and 35, the success rate is 73%. In a couple with a woman between 35-40 years of age, the success rate is higher, the younger the male partner is. In natural conception, increasing male age is associated with a decreased likelihood of becoming pregnant, an increased time to conception, and an increased risk of preterm birth or miscarriage. Although the mechanisms behind this process are still unclear, scientists suggest that they are caused by reduced semen quality, an increased incidence of DNA damage in sperm, and epigenetic changes in sperm that affect fertilization, implantation, or embryonic development.