Female Fertility Factors and Statistics
The average age of girls when they get their first menstrual period is around 12.5 years. During the first year after the first menstrual period occurs in girls, 80% of the cycles do not produce eggs and this percentage reduces to 5 in the second year and by the time the girls enter the sixth year, this percentage reduces to 10.
A woman is most fertile when she is between 20 and 35 years of age. Theoretically, the age of menopause in women is between 45 and 55 years, but then a lot of women go through this phenomena earlier and later than this defined age too. In the process of menopause, the ovaries gradually stop functioning as a result of which the production of eggs by them stops and so does the creation and shedding of uterine lining. As the menopause sets in, the fertility of a woman ends.
Henri Leridon, PhD, who is an epidemiologist with the French Institute of Health and Medical Research, has given some figures relating to women wanting to conceive without the help of any of medicines and medical procedures, and as per those figures, if the age of a woman is 30 years, there are 75% chances that she will conceive and give birth within one year and there are 91% chances that she will conceive and give birth within 4 years. If the age of a woman is 35 years, the chances of conception and giving birth within one year are 66% and those for conception and birth within 4 years are 84%. If the age of woman is 40 years, the chances of her conception and giving birth in one year are 44% and that within 4 years are 64%.
Certain fertility medicines and procedures such as in vitro fertilization have been known to help women in conception at age as late as 67 years too. There have been some studies done since 2004 and those have shown that mammals may produce new eggs all their lives. According to the researchers at the Massachusetts General Hospital in Boston, America, the theories of female fertility being limited with age will be changed if humans can also produce new eggs every month, but this is still only a speculation and nothing can be said about it with confirmation.
The non profit organization of USA, the March of Dimes, which works for the health improvement of mothers and babies, has observed that about 9% of pregnancies in the women between 20 and 24 years, end in a miscarriage, and this percentage increases to approximately 20 in the women of age group 35 and 39 years, and it increases further to 50 for women above 40 years in age. Along with the probability of miscarriages, the chances of birth defects because of chromosomal anomalies also increase with age in women. The chances of Down Syndrome in the new born of a 25 year old mother are 1 in 1250, whereas the chances of this disease in a 30 year old mother's new born are 1 in 1000 and they become 1 in 400 when the mother's age is 30 and 1 in 100 when the mother's age is 40 and 1 in 30 when the mother is 45 years old.
Male Fertility Statistics
The volume of semen, the sperm morphology as well as their mobility reduces with the increase in age of men. The ability to impregnate women reduces from 38% in men below the age of 30 years to 23% in men over 50 years of age.
Men who are in the age group of 20 to 50 years produce 75% more sperm that men above 50 years of age. Along with sperm count, another aspect that needs to be considered is the presence of seminiferous tubules in the testes of sperms. Men between 20 and 39 years of age have 90% of seminiferous tubules containing mature sperm, whereas this percentage reduces to 50% for men in the age group of 40 and 69 and it reduces further to 10% for men older than 80 years of age.
It has also been observed that men who become fathers at a later age, their children are more likely to develop a number of health issues. During an Israeli study, the risk of Autism was seen 5.75 times more for the children who were born to fathers who were 40 years old or higher. Another major disease linked with age of fathers and their new borns is Schizophrenia which is more likely to develop in babies whose fathers are 40 or above.
An Australian study shows that the sperm health of men is also affected by obesity. The chances of fertilization reduce by 40% for men who are obese. Various countries have different age limit for men who can donate sperm and this age is 50 years in USA and 40-45 years in the UK.