Transactions of the Twenty-Sixth Annual Meeting of the Society for Maternal-Fetal Medicine
Maternal age and the risk of stillbirth throughout pregnancy in the United States

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Objective

The objective of the study was to examine the relationship of maternal age with stillbirth risk throughout gestation.

Study design

A total of 5,458,735 singleton gestations without reported congenital anomalies from the 2001 to 2002 National Center for Health Statistics perinatal mortality and natality files were analyzed. Hazard rates (risk) of stillbirth (fetal death 20 weeks or longer) were calculated for each week of gestation.

Results

The risk of stillbirth at 37 to 41 weeks for women 35 to 39 years old was 1 in 382 ongoing pregnancies and for women 40 years old or older, 1 in 267 ongoing pregnancies. Compared with women younger than 35 years old, the relative risk of stillbirth was 1.32 (95% confidence interval 1.22, 1.43) for women 35 to 39 years old and 1.88 (95% confidence interval 1.64, 2.16) for women 40 years old or older at 37 to 41 weeks. This effect of maternal age persisted despite accounting for medical disease, parity, and race/ethnicity.

Conclusion

Women who are of advanced maternal age are at higher risk of stillbirth throughout gestation; the peak risk period is 37 to 41 weeks.

Section snippets

Material and methods

The sources of data were National Center for Health Statistics perinatal mortality and natality files for 2001 and 2002 combined. We selected the following 36 states for analyses because they met the criteria of 80% or greater complete reporting for the specific data entry fields on Hispanic origin, method of delivery, and prenatal care history: Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland,

Results

We analyzed 5,458,735 singleton, nonanomalous gestations from 2001 to 2002. The maternal age distribution of the total population was 87.4% for younger than 35 years, 10.4% for 35 to 39 years, and 2.2% for older than 40 years. The overall cumulative hazard for stillbirth per 1000 pregnancies through 41 weeks' gestation was 6.5.

The Figure depicts the hazard (risk) of stillbirth per 1000 ongoing pregnancies for each week of gestation from 20 to 41 weeks according to maternal age. The cumulative

Comment

Increasing numbers of women are electing to delay or continue child-bearing beyond age 35 years in the United States. The percentage of total births in the United States to women 35 years old or older increased from 4.5% in 1978 to 13.8% in 2002.11, 12 This study is the first to provide an estimate of stillbirth risk in ongoing pregnancies throughout gestation in advanced maternal age women based on U.S. vital statistics data from 2001 to 2002. This approach provides a clinically relevant

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    Presented at the 26th Annual Meeting of the Society for Maternal-Fetal Medicine, January 30 through February 4, 2006, Miami, FL.

    Reprints not available from the authors.

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