A woman is normally born with a fixed number of egg follicles meant for development and maturation of the eggs and this number is known to only diminish as she grows up, denoting the number of eggs at birth would be all that she is going to have in her lifetime (although there have been recent evidences where it has been shown that female mammals like mice can indeed replenish the reproductive follicle pool when the damaged eggs die). As she grows up, her eggs age with her, decreasing in quality and quantity. This is the time when ovulation becomes irregular as compared to her younger years when the menstrual cycle is regular and there is ovulation every month.

In her younger years, in the beginning of each menstrual cycle when a woman is having her period, a hormone produced in the pituitary gland, which is located in the brain, stimulates a group of follicles to grow more rapidly on both ovaries. The pituitary hormone that stimulates the ovaries is called follicle-stimulating hormone (FSH). Normally, only one of these follicles will reach maturity and release an egg (ovulate); the remainder gradually will stop growing and degenerate. Pregnancy results if the egg becomes fertilized and implants itself in the uterine endometrium. If pregnancy does not occur, the endometrium is shed as the menstrual flow and the cycle begins again. In their early teens, girls often have irregular ovulation resulting in irregular menstrual cycles, but by the age of 16 their ovulation cycle gets regulated resulting in regular periods. A woman’s cycles will remain regular, 26 to 35 days, until her late 30s to early 40s when she may notice that her cycles become shorter. As time passes, she will begin to skip ovulation resulting in missed periods. Ultimately, periods become increasingly infrequent until they cease completely. When a woman has not had a menstrual period for 1 full year, she is said to be in menopause.

This is why age is regarded as the single most important factor affecting a woman’s fertility. While good health improves the chance of getting pregnant and having a healthy baby, it does not override the effects of Aging female fertility.

In her early to mid-20s, a woman has a 25 to 30 per cent chance of getting pregnant every month. Female fertility generally starts to decline when a woman is in her early 30s, and the decline speeds up after the age of 35. By age 40, the chance of getting pregnant in any monthly cycle is down to around five per cent. However, there lies a common misconception that IVF treatment can overcome age-related infertility. A woman’s age also affects the chance of success with IVF as the older she gets, the reproductive health diminishes, even if it is by a tiny fraction.

Women do not remain fertile until menopause. The average age for menopause is 51, but most women become unable to have a successful pregnancy sometime in their mid-40s.

For Aging female (aged upwards of 35) the chance of having a baby increases if they use eggs donated by a younger woman.

The risk of pregnancy complications increases with age too. The risk of miscarriage and Pregnancy risks and chromosomal abnormalities in the fetus increase significantly from age 35. As she grows older, she becomes more prone to developing complications such as gestational diabetes, placenta previa (when the placenta covers all or part of the cervix, which increases the risk that the placenta will detach), caesarean section, and still birth, which although are not limited to only the older women, but are definitely more common than their younger counterparts.

It is not only that the baby’s health is at stake, but also the mother’s health which is at a risk of conditions like preeclampsia. Some of the increase in risk may be because older women tend to have more health problems before they get pregnant than younger women. For example, having high blood pressure, a condition that becomes more common with age, can increase the risk of preeclampsia. Studies also show that older women who do not have any health conditions still can have complicated pregnancies.

The rate and chances of babies born with chromosomal abnormalities also increases when elderly women try to conceive. This is because of the diminishing quality of eggs with age. One such important change in egg quality is the frequency of genetic abnormalities called aneuploidy (too many or too few chromosomes in the egg). At fertilization, a normal egg should have 23 chromosomes, so that when it is fertilized by a sperm also having 23 chromosomes, the resulting embryo will have the normal total of 46 chromosomes. As a woman gets older, more and more of her eggs have either too few or too many chromosomes, implying that if fertilization occurs, the embryo also will have too many or too few chromosomes. Most people are familiar with Down syndrome, a condition that results when the embryo has an extra chromosome 21. Most embryos with too many or too few chromosomes do not result in pregnancy at all or result in miscarriage. This helps explain the lower chance of pregnancy and higher chance of miscarriage in older women. The risk of having a baby with Down syndrome is

• 1 in 1,480 at age 20 years
• 1 in 940 at age 30 years
• 1 in 353 at age 35 years
• 1 in 85 at age 40 years
• 1 in 35 at age 45 years

Genetic screening is recommended for parents who start a family later than usual in order to prevent babies bring born with such genetic abnormalities.