How Does Age Affect Fertility : Pregnancy Over Age 30

Many women today are waiting until later in life to have children. In the United States, birth rates for women in their 30s are at the highest levels in three decades. However, an older mother may be at increased risk for miscarriage, birth defects, and pregnancy complications such as twins, high blood pressure, gestational diabetes, and difficult labors. Some studies show that while there may be a greater likelihood of pregnancy complications in older women, their babies may not have more problems than babies of younger women. This is more likely when women receive prenatal care and give birth in a healthcare facility equipped to care for high-risk mothers and babies.

Risks for Chromosome Abnormalities by Maternal Age

Maternal Age	Down syndrome	Any abnormality
15 to 24 years	1/1300	1/500
25 to 29 years	1/1100	1/385
35 years	1/350	1/178
40 years	1/100	1/63
45 years	1/25	1/18

It is possible that risks may be higher as many statistics only report live births and do not take into account pregnancies with chromosomal abnormalities that were terminated or ended due to natural pregnancy loss. There are approximately 400 different types of chromosome abnormalities that have been observed in humans, however, many are rare. The risk for Down syndrome makes up almost half of the maternal age risk for chromosome abnormalities.

In general, for women under the age of 40, after having one child with Down syndrome, the chance of having another baby with Down syndrome is 1 percent. After age 40, the recurrence risk for Down syndrome is based on the age of the mother at delivery. It is important to know that about 75 percent of babies with Down syndrome are born to women under the age of 35. This is because women under the age of 35 have more babies than women over 35. The physician may refer parents to a genetic specialist or genetic counselor who can explain the results of chromosomal tests in detail, including what the recurrence risks may be in another pregnancy and what tests are available to diagnose chromosome problems before a baby is born.