Birth outcomes across the spectrum of maternal age: dissecting aging effect versus confounding by social and medical determinants

Role of Maternal Age in Increasing Severe Maternal Morbidity Rates in the United States

OBJECTIVE

To evaluate a commonly proposed explanation for increasing rates of severe maternal morbidity (SMM) in the United States: shifts in the birthing population to older maternal ages, a known risk factor for SMM.

METHODS

We conducted a cross-sectional analysis comparing delivery hospitalizations from two time points (2008-2009 to 2017-2018) using hospital discharge data from the National Inpatient Sample. We used demographic decomposition techniques to evaluate whether increasing rates of SMM and nontransfusion SMM were explained by population-level increases in maternal age or changes in age-specific rates. Analyses were stratified by race and ethnicity.

RESULTS

Rates of SMM and nontransfusion SMM significantly increased in the United States between 2008 and 2018 from 135.6 to 170.5 and 58.8 to 67.9 per 10,000 delivery hospitalizations, respectively, with increases observed for nearly all racial and ethnic groups. Over this same period, the proportion of births to people younger than age 25 years decreased and births to people of advanced maternal age (35 years and older) increased, with the largest increases occurring among people identified as non-Hispanic American Indian/Alaskan Native (9.8-13.0%), non-Hispanic Black (10.7-14.4%), and Hispanic (12.1-17.1%). Decomposition analyses indicated that the changing maternal age distribution had little effect on SMM trends. Rather, increases in SMM and nontransfusion SMM were primarily driven by increases in age-specific SMM rates, including rising rates among younger people. Contributions of maternal age shifts were minimal for all racial and ethnic groups except among non-Hispanic Black people, for which 17-34% of the rise in SMM was due to increasing maternal age.

CONCLUSION

Except among certain racial groups, increases in U.S. population-level SMM rates over the past decade were due to increases in age-specific rates rather than shifts to older maternal age among the birthing population. Increasing SMM rates across the maternal age spectrum could indicate worsening prepregnancy health status of the birthing population.

Telomeres, oxidative stress, and timing for spontaneous term and preterm labor

Telomeres are nucleoprotein complexes located at the distal ends of chromosomes. In adults, progressive telomere shortening occurs throughout the lifetime and is thought to contribute to progressive aging, physiological senescence, multiorgan dysfunction, and ultimately, death. As discussed in this review, multiple lines of evidence provide support for the biological plausibility that a telomere-based clock mechanism also determines the length of gestation, leading to the onset of labor (parturition). After telomere expansion at the beginning of pregnancy, the telomere lengths in the gestational tissues (ie, the placenta and fetal membranes) progressively shorten throughout the remainder of pregnancy. The rate of telomere shortening can be accelerated by conditions that affect the mother and result in oxidative stress. Preterm births in the United States are associated with multiple risk factors that are linked with increased oxidative stress. Antioxidant vitamins (ie, vitamins E and C) mitigate the effects of oxidative stress and delay or prevent telomere shortening. Clinical trials with vitamins E and C and with multivitamins started during the periconception period have been associated with reduced rates of preterm births. In the United States, African-American women have a 2-3-fold higher rate of preterm birth. African-American women have multiple risk factors for premature birth, all of which are distinct and potentially additive with regard to epigenetic telomere shortening. The "weathering effect" is the hypothesis to explain the increased rates of chronic illness, disabilities, and early death observed in African-Americans. With regard to pregnancy, accelerated weathering with the associated telomere shortening in the gestational tissues would not only explain the preterm birth disparity but could also explain why highly educated, affluent African-American women continue to have an increased rate of preterm birth. These studies suggest that the racial disparities in preterm birth are potentially mediated by telomere shortening produced by lifetime or even generational exposure to the effects of systemic racism and socioeconomic marginalization. In conclusion, this review presents multiple lines of evidence supporting a novel hypothesis regarding the biological clock mechanism that determines the length of pregnancy, and it opens the possibility of new approaches to prevent or reduce the rate of spontaneous preterm birth.