March 28, 2014 — Summary of "Female Age-Related Fertility Decline," American College of Obstetricians and Gynecologists Committee on Gynecologic Practice/Practice Committee of the American Society for Reproductive Medicine, Obstetrics & Gynecology, March 2014.
A woman's fertility "decreases gradually but significantly beginning approximately at age 32 years and decreases more rapidly after age 37 years," according to a committee opinion by the American College of Obstetricians and Gynecologists Committee on Gynecologic Practice and the Practice Committee of the American Society for Reproductive Medicine.
Biological Bases for Age-Related Fertility Decline
The number of oocytes in a woman's ovaries "naturally and progressively" decreases as the ovaries age, the opinion explains. The number of oocytes that exist in a woman's body begins at approximately six million to seven million at 20 weeks of gestation in the female fetus and declines to about 1,000 by age 51, which is the average age women begin menopause in the U.S.
The decrease in fertility in a woman's 30s primarily represents lower egg quality associated with "a gradual increase in the circulating level of follicle-stimulating hormone and decreases in circulating antimullerian hormone and inhibin B concentrations," according to the opinion. It notes that while "it is difficult to separate out the effects of sexual behavior from age," given that sexual activity also tends to decrease with age, research involving insemination and in vitro fertilization suggests that younger women -- and younger eggs, in donor situations -- are more likely to produce live births.
The committees note that other factors can contribute to early fertility decline, including "prior ovarian surgery, chemotherapy, radiation therapy, severe endometriosis, smoking, pelvic infection, or a strong family history of early menopause."
In addition, age-related fertility decline is "accompanied by significant increases in the rates of aneuploidy and spontaneous abortion," the opinion states.
"[G]iven the anticipated age-related decline in fertility, the increased incidence of disorders that impair fertility, and an increased risk of pregnancy loss, women older than 35 years should receive an expedited evaluation and undergo treatment after 6 months of failed attempts to conceive or earlier, if clinically indicated," the opinion recommends.
In women older than age 40, "immediate evaluation and treatment are warranted," according to the committees.
In addition, the opinion stresses that "[e]ducation and enhanced awareness of the effect of age on fertility is essential in counseling the patient who desires pregnancy."