Researchers also found black mothers who were single when they had their first child and remained unmarried had better health at age 40 than those who later married.
Lead study author Kristi Williams, associate professor of psychology at Ohio State University, and colleagues found that women who had their first child between the age of 25-35 reported better health at the age of 40 than those who had their first child as a teenager (15-19) or in early adulthood (20-24).
Interestingly, however, the team found that the health of women who had their first child as a teenager was no better at the age of 40 than those who had their first child in early adulthood.
"Ours is the first US study to find that having your first child in young adulthood is associated with worse self-assessed health decades later for white and black women, when compared to those who wait until they are over 24," notes Williams.
The study was recently published in the Journal of Health and Social Behavior.
Worse health for women who become mothers aged 24 and younger
The team reached their findings by analyzing data of 3,348 women who were part of the National Longitudinal Survey of Youth 1979 (NLSY79).
All women had a first birth between the ages of 15-35 and completed health questionnaires every 1 or 2 years between 1979-2008.
The researchers compared the health data of women who gave birth at ages 15-19, 20-24 and 25-35, focusing specifically on their self-reported health at the age of 40.
Women who had their first child at age 25-35 reported better health at the age of 40 than those who had their first child as a teenager or in early adulthood; the two younger groups reported similar health at the age of 40.
The researchers say the latter finding challenges the popular notion that it is better to wait until young adulthood to have a first child.
"We've had all this focus on the bad effects of teen childbearing and never really asked what happens if these teens waited to early adulthood," says Williams. "The assumption has been that 'of course, it is better to wait.' But at least when it comes to the later health of the mother, that isn't necessarily true."
Marriage may not benefit midlife health of single mothers
Additionally, the researchers found that a woman's marital status at the time of her first child may influence her midlife health.
Fast facts about births in the US
- There were 3,932,181 births in the US in 2013
- The average age of first births for women in 2013 was 26
- Around 40.6% of women who gave birth in 2013 were unmarried.
Overall, women who were married when they had their first child reported better health at the age of 40 than those who were unmarried at the time of their first child.
Among black women, however, those who were single when they had their first child and who remained unmarried reported better midlife health than those who later married - a finding the researchers say negates public policies that encourage single mothers to marry.
"Most studies indicate that marriage promotion efforts have been unsuccessful in increasing marriage rates," notes Williams. "Our findings suggest that may be a good thing, at least for black women's health."
While the team is unable to pinpoint the reasons behind the potential negative health effects of later marriage among single black mothers, they cite earlier studies that suggest many black single mothers are unable to find men with good economic prospects; those who marry are likely to have a husband with poor education and low income.
"That can lead to stress and conflict in marriage, which can result in poorer health for the women as they age," notes Williams.
Findings a cause for concern
Speaking of their overall findings, the team says the fact that women who had their first child in early adulthood reported worse midlife health than those who had their first child in later adulthood is worrying; around one third of first births in the US occur among women aged 20-24 - mostly among single mothers.
What is more - while the number of teenage births among black women has fallen in recent years - the researchers note that around 63% of all first births among black women occur among those under the age of 24.
"We still need to be concerned that women who are having births in their early 20s may face more health challenges as they reach middle age than those who wait longer."
It is not only women's midlife health that may be affected by the timing of their first child. Earlier this year, Medical News Today reported on a study suggesting men who become fathers before the age of 25 may be at greater risk of death in middle age.