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Clinical Obstetrics

Poster Session 1

(278) Is Age Just a Number? Advanced Maternal Age and Stillbirth Risk

Tuesday, February 13, 2024
10:30 AM – 12:00 PM  
Location: Prince George's Exhibit Hall CDE, Lower Atrium Level
Objective: Advanced maternal age (AMA) has been associated with an increased risk of stillbirth, but it is unclear whether this is an independent effect or represents risk of higher baseline morbidity with increasing age. Further, it is not obvious whether these stillbirths are preventable either by antenatal testing or indicated delivery. The objective of this study is to assess risk of stillbirth in a large population among women classifying as AMA. 

Study Design: This was a population based retrospective study of all singleton, non-anomalous, genetically normal gestations ≥ 20 weeks gestational age in a national registry of live birth vital statistics data from 2020-2022. Women were stratified by age categories in five-year increments from 15-49 years old. Conditional stillbirth rates were calculated per 10,000 women for each gestational age week between 28-41 weeks. Poisson regression with robust error variance was used to calculate adjusted risk ratios (aRR) for still birth overall and ≥ 32 weeks in ongoing pregnancies adjusting for chronic hypertension, pregestational diabetes, and birthweight percentile with age 25-29 as the referent. A secondary analysis restricted the regression to patients with delivery <40 weeks.

Results: A total of 7,032,369 pregnancies were included in this analysis with 15.8%, 3.4%, and 0.2% with maternal age of 35-39, 40-44, and 45-49, respectively. Conditional stillbirth rates increased with advancing gestational age in all groups, with a notable increase following 39; Figure 1. Absolute overall risk of stillbirth was small (range 0.42%-0.85%) with the highest rate at 45-49 years old. The risk of stillbirth after 32 weeks was only significant in women age 40-44 (aRR 1.18, CI 1.07-1.29) and age 45-49 (aRR 1.49, CI 1.10-1.99) after adjustment. However, when further adjusting to exclude deliveries occurring after 39 weeks there were no significantly increased risks of stillbirth across any age category. 

Conclusion: A small but significant increased risk of stillbirth was seen in women 40 to 49 years old. However, this was not significant restricting to women delivered < 40 weeks.