In 2011, nearly 30% of women who gave birth to single infants had an interval of less than 18 months between the conception of their most recent pregnancy and the birth of their previous child, potentially putting them at risk for pregnancy complications.
The findings, released April 16, come from a new report from researchers at the Centers for Disease Control and Prevention, who analyzed birth certificate data covering 1,723,084 women who had singleton births in 2011. In addition to women with short birth intervals, the report found that nearly 21% of women had birth intervals of 60 months or longer, which is also associated with a higher risk for adverse health outcomes, the researchers wrote (National Vital Statistics Report 2015;64:1-10).
About half of women had an interval of 18-59 months between the birth of one child and the conception of the next child, the researchers found.
Age and race had an impact on the birth interval, according to the birth certificate data. The median interpregnancy interval increased along with the age of the mother. For instance, the median interpregnancy interval was 11-14 months for women under age 20 years, but it was 39-76 months for women aged 40 years and older. Non-Hispanic white women had the shortest median interpregnancy interval at 26 months. This is compared with 30 months for non-Hispanic black women and 34 months for Hispanic women.
The birth certificate data used in the study, from 36 states and the District of Columbia, is not nationally representative and may not be generalizable across the United States, but the researchers pointed out that the percentages of women with short and long pregnancy intervals were similar to pregnancy data from the 2006-2010 National Survey on Family Growth.
The researchers called for further studies to assess whether pregnancy intervals are “independently associated with adverse maternal and infant health outcomes or whether these relationships are due to other confounding factors” such as maternal age, socioeconomic status, and pregnancy health behaviors.
Find the full study here.