AGE AND FERTILITY
For women, the fertility declines with increasing age and the chromosomal abnormalities also increase.
Women have a finite number of eggs in their ovaries. They are born with approximately two million eggs in their ovaries, but about eleven thousand of them die every month prior to puberty a lifetime, through a process known as atresia. Atresia begins at birth and continues throughout the course of the reproductive life. When puberty is reached and menstruation begins, only about 400,000 follicles remain.
With each menstrual cycle, a thousand follicles are lost and each cycle one egg matures to ovulate. That means that of the one to two million follicles, only about 400 will ever mature.Relatively little or no follicles remain at menopause, which usually begins between 48 to 55 years of age.
Two main hormones responsible for both ovulatory cycles and menstrual cycle are Follicle stimulating hormone (FSH) and luteinizing hormone (LH), and are released from the brain and travel in the blood to the ovaries. The FSH hormone stimulates the growth of about 15 to 20 eggs in the ovaries, in each cycle, however, due to micro level changes in the hormones, one follicle becomes dominant and the rest are atretic, at the same time estrogen levels rise, which like a switch, decrease follicle-stimulating hormone. This careful balance of hormones allows the body to limit the number of follicles that mature. The dominant follicle reaches a critical size at which time ovulation is triggered from the LH and egg released. The follicle now starts producing progesterone in preparation for pregnancy. If pregnancy continues, the follicle becomes the support for pregnancy till placenta develops. If not, there is bleeding and the cycles repeat in the same pattern.
Increase in age is associated with high Incidence of Downs Syndrome, Patau’s and Edwards. Aneuploidy is due to aging of the eggs and abnormalities in fertilization.
Male fertility decline is more subtle, but a man’s age affects the chances of his (female) partner conceiving, and increases the risk of miscarriage and the child’s risk of mental health and developmental disorders.