Medically Assisted Reproduction in the United States: A Focus on Parents 40 and Older.

As age at first birth continues to increase in the United States, the use of medically assisted reproduction (MAR) has likely increased. Using population-level data of births in the United States from the National Vital Statistics System from 2010 to 2021, the authors document the proportion of births due to MAR with a focus on parents 40 years or older, disaggregating by parental age combinations and parity. Although MAR-related births constitute a small proportion of all births, there is a growing and sizable proportion of first births to women 40 years or older due to MAR. Specifically, 28.2 percent, 21.5 percent, and 15.3 percent first births involved MAR among mothers 40 or older with an unknown father's age, both parents 40 or older, and mothers 40 or older with fathers younger than 40, respectively. Thus, for some groups, MAR is a particularly important component of the pathway to parenthood.