Delayed childbearing: more women are having their first child later in life.

Of particular interest to both researchers and the public is the "average" age of women when they have a child, especially their first. Age at first birth influences the total number of births that a woman might have in her life, which impacts the size, composition, and future growth of the population. The age of the mother, both younger and older, plays a strong role in a wide range of birth outcomes (e.g., birthweight, multiple births, and birth defects), so it is critical to track the average age at which women have their first birth.