Trends in Birth across High-Parity
The published evidence showing that high-parity women are at greater risk for adverse birth outcomes is inconclusive. Whereas some studies find a direct association between parity status and adverse birth outcomes, others do not. In order to understand the linkage between parity status and adverse birth outcomes, it may be necessary to investigate temporal changes within certain sociodemographic entities, a step that could provide etiologic clues to these findings. However, it remains unknown whether the proportion of births to high-parity women has changed over the past decades, reflecting certain shifts in the demographic composition of gravidas in the United States. This issue is important, as the demography of the country continues to expand and diversify. For instance, during the last half of the 20th century, racial and ethnic diversity increasingly characterized the population of the United States. As of 1998, immigrants comprised approximately 9% of the U.S. population and, consequently, the proportion of births to foreign-born women has risen. In addition, the age distribution of pregnant women in the United States has changed. Whereas childbearing among women in their 20s has slightly declined or remained stagnant, birth rates for women aged >35 have increased consistently.
As a result of the aforementioned demographic trends among childbearing mothers in the United States, we sought to examine whether these changes have affected birth rates to parous mothers. The primary aim of this study was to explore temporal variations in live-born parity by race and maternal age in the United States from 1989 through 2000. While considering that adverse outcomes are more common with advanced age and high parity, we undertook the study with the following specific objectives:
1. Determine temporal trends in birth rates to women across live-born parity subgroups in the United States from 1989-2000.
2. Assess temporal variations in birth rates by race/ethnicity within each parity category.
3. Estimate racial and ethnic differences in birth rates across the parity subgroups after taking into account the overall contribution of observed maternal age-related trends in birth rates.
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