It is currently believed that women are born with between 1 and 2 million eggs, with the number decreasing throughout life. A gradual decline in fertility begins around age 32 and continues to decrease rapidly after age 37 because of the reduction in the number and quality of eggs in the ovaries.1 The lower number of eggs leads to changes in hormone levels, which further reduces a woman's fertility.
New research suggests that eggs can be made from stem cells in the ovaries.2 This finding challenges the belief that women are born with a certain number of eggs, and the discovery could help women undergoing early menopause or preserve fertility for women undergoing cancer treatment.
Increasing age also increases the risk for certain diseases that can contribute to a loss of fertility. These include:
In addition, women with a history of ovarian surgery, chemotherapy, radiation therapy, severe endometriosis, smoking, or pelvic infections may have premature reduction in the number of eggs in the ovaries and a simultaneous reduction in fertility.
As a woman ages, the risk increases for miscarriage and for having an embryo with abnormal chromosomes, which can lead to problems with development and loss of the pregnancy.
Because of the decrease in fertility, women older than age 35 who have not been able to get pregnant after 6 months of unprotected sex should consult with a health care professional.
Some women are able to conceive but are not able to carry a pregnancy to term. If loss of the pregnancy occurs before 20 weeks of gestation, it is called a miscarriage. If the loss occurs after 20 weeks of gestation, it is called a stillbirth. When multiple losses of pregnancy occur, it is called repeated or recurrent miscarriage. Women should seek medical advice after two or more failed pregnancies to determine the cause.3
Abnormal chromosomes (structures that contain DNA) in the embryo cause more than 50% of miscarriages that occur during the first 13 weeks of pregnancy.4 In cases of repeated miscarriage, abnormalities in the mother's or father's genes may prevent an embryo from developing.
Many other factors affect the risk of having repeated miscarriages. These include5:
In at least half of stillbirths, the cause cannot be identified.6
More information on miscarriage or stillbirth can be found at the NICHD Pregnancy Loss topic page.
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