Fertility in women above 35 years of age

27 Jul

Fertility in women above 35 years of age

As more women choose to put off pregnancy to their 30’s to pursue other life goals, the question of fertility with advanced age becomes important. Although fertility in women is impaired by various factors such as obesity, smoking, medical conditions and other lifestyle variables, age continues to be the biggest contributing factor to decreased fertility. Even by leading healthier lifestyles, it is not possible for women to offset the decline in fertility that comes with age.

Relationship between age and fertility

During the reproductive years between puberty and menopause, women have regular menstrual cycles. In each cycle, one egg matures inside the follicles in one of the ovaries and is released. If the egg is fertilized by sperm, it implants in the uterine lining resulting in pregnancy. If not, the uterine wall is shed as menstrual flow. Typically the menstrual cycle lasts between 26 to 35 days until women reach their late 30’s and early 40, beyond which the cycle becomes shorter. During the same period, the fertility with age women also continues to decline as the number of egg-containing follicles in the ovaries continues to decline. At birth, females have about a million follicles, by puberty which decreases to about 300,000. Throughout their reproductive years, only about 300 follicles produce a mature egg during ovulation.

The peak reproductive years for women are in their 20’s. By the time they reach 30, their fertility begins to decline, particularly after the age of 35 gradually. Statistically, a fertile 30-year-old woman only has about a 20% chance of getting pregnant in 1 cycle. That is, 20 women out of 100 fertile women in their 30’s can get pregnant on their first try. The remaining 80 women will have to try again. By the time women reach their 40’s their chances of getting pregnant in 1 cycle drops to 5%. When women reach their mid to late 40’s they are unable to have a successful pregnancy as the average age for menopause is 51, and women do not remain fertile until then.

Causes for age-related infertility

Fertility after 35 in women begins to decline because of two main reasons:

Egg Quality

The quality of the eggs decreases along with the number of eggs as women reach their mid to late 30’s. Genetic abnormalities begin to increase in frequency, leading to decreased egg quality. Embryos that have too few chromosomes or too many as a consequence do not result in a pregnancy or end in a miscarriage. The incidence of Down syndrome, where the embryo has an extra chromosome, also increases.

Egg Quantity

As women reach their late 30’s, their ovarian reserve begins to decrease. Since the existing pool of follicles is used up, they become less sensitive to FSH stimulation. This results in the menstrual cycles becoming shorter. Gradually the follicles stop responding consistently enough to ovulate periodically, which results in longer and irregular cycles. Ovarian reserves can also decrease prematurely due to lifestyle factors such as smoking, ovarian surgery or a family history of premature menopause.

Conclusion

Women’s fertility begins to decline as they get to their early 30’s gradually. Women’s fertility over 35 begins to drop at a faster rate as the quantity and quality of the follicles go into a fast decline.

References:

https://www.reproductivefacts.org/news-and-publications/patient-fact-sheets-and-booklets/documents/fact-sheets-and-info-booklets/age-and-fertility/

https://fertilitynetworkuk.org/fertility-faqs/factors-affecting-fertility/