Extremes of maternal age are associated with adverse outcomes in pregnancy. Age at the time of delivery of less than sixteen years or greater than thirty-five years meets the criteria for this definition. Young women have a higher incidence of premature delivery, high blood pressure, and small infants. In women over age thirty-five, chronic diseases such as diabetes and high blood pressure become more common. In addition, the aging of the developing eggs in the ovary is associated with an increased risk for spontaneous miscarriage and the birth of infants with chromosomal abnormalities such as Down syndrome and Edwards syndrome. As an example, at age thirty-five a woman's risk for the delivery of an infant with Down syndrome is 1 in 378; by age forty-five this risk has increased dramatically to 1 in 30. Tests that sample the amniotic fluid around the developing fetus (amniocentesis) or sample a small part of the placenta (chorionic villus biopsy) can be undertaken to determine if the chromosomal makeup of the fetus is normal.
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