Researchers from University of Maastrict have found the reasons for the increased probability of boy children's born to women older than 35 years of age. Professor Luc Smits have reported the results of the work in British Medical Journal analyzing data of child births in 5,283 women and found that there is an probability of 58% of getting male child in women who took more than a year to get pregnant. The researchers also have noted that the there is a 4% increased probability of getting male child for each additional year.
The Researchers feel that the viscosity and stickiness of the cervix mucus is responsible for increased probability of getting boy child in late pregnancy in women. The mucus in the cervix becomes thicker and sticky in women who take longer time to get pregnant which makes the sperm hard to migrate and reach the ovum. But, the Y chromosome bearing sperm is lighter and has the capacity to swim faster through the thickened cervix and reaches the ovum which increases the probability of getting male child.