Premature delivery linked to greater risk of early death in women and threat may remain for next 40 years: Study
Preterm and early term delivery are independent risk factors for premature death in women and the risk can persist for up to 40 years after delivery, according to researchers. Preterm is defined as babies born before 37 weeks of pregnancy are completed, while early-term implies giving birth between 37-38 weeks of pregnancy.
After taking account of many other risk factors, the authors found that women who delivered preterm or extremely preterm (22-27 weeks) had 1.7-fold and 2.2-fold increased risk of death from any cause, respectively, during the next 10 years compared with those who delivered full term. This equates to around 28 excess deaths per 100,000 person-years. These risks subsequently declined but remained significantly raised even 20-44 years after delivery, more than 1.3-fold in preterm delivery, and 1.6-fold in extremely preterm delivery, reveals analysis.
The findings were not explained by shared genetic or early life environmental factors in families. “This suggests that women who deliver prematurely need long term clinical follow-up for detection and treatment of chronic disorders associated with early mortality,” recommends the research team from the Icahn School of Medicine at Mount Sinai, US and Lund University, Sweden.
Nearly 11% of all births worldwide occur preterm, says the study. Preterm birth has been associated with long term health risks, not only in children but also in mothers. Women who deliver preterm or extremely preterm have been reported to have increased risks of developing conditions such as heart disease or diabetes in later life, but little is known about their long term risk of death. A better understanding of these outcomes is needed to identify women at high risk and guide their long term clinical care, say experts.
Accordingly, a team led by Professor Casey Crump at the Icahn School of Medicine at Mount Sinai, set out to examine the long-term death associated with preterm delivery in women and to explore the potential influence of shared genetic or environmental factors within families. Using nationwide birth records, they analyzed data on length of pregnancy for over two million women who gave birth in Sweden during 1973-2015. Deaths were then identified from the Swedish Death Register up to December 31, 2016, with a maximum follow-up time of 44 years.
Overall, 76,535 (3.5%) of women died, at an average age of 58. Compared with full-term delivery, women who delivered preterm, extremely preterm, or early term had 1.41-fold, 1.7-fold, and a 1.11-fold higher risk of death, respectively. “In the first 10 years after delivery, the adjusted hazard ratio for all-cause mortality associated with preterm delivery was 1.73. When further stratified, it was 2.20 for extremely preterm delivery, 2.28 for very preterm delivery (28-33 weeks), 1.52 for late preterm delivery (34-36 weeks), and 1.19 for early term delivery compared with full-term delivery (39-41 weeks),” the findings reveal.
The analysis shows that whereas risks were highest in the first 10 years after delivery and then declined, absolute differences in death associated with preterm delivery increased with longer follow-up times. For example, there was a 1.5-fold increased risk (equivalent to 48 excess deaths per 100,000 person-years) 10-19 years after delivery, and a 1.4-fold increased risk (equivalent to 143 excess deaths per 100,000 person-years) 20-44 years after delivery. “Overall, an estimated 2,654 excess deaths in this population were associated with preterm delivery -- one excess death for every 73 women who delivered preterm. Even early term delivery (37-38 weeks) was associated with modestly increased mortality risks that persisted 20-44 years later,” says the report.
The team identified several specific causes of death associated with preterm delivery, which include cardiovascular and respiratory disorders, diabetes and cancer. The findings did not seem to be attributable to shared genetic or environmental factors within families.
Since this is an observational study, it cannot establish cause and the researchers acknowledge some limitations, such as a lack of complete information on spontaneous or medically indicated preterm delivery. However, strengths include the large sample size and long follow-up time, prompting the authors to say that premature delivery should now be recognized as a risk factor for early death in women that can remain raised up to 40 years later.