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Maternal age and risk of preterm birth

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Pregnant mothers aged 40 and over may have an increased risk for preterm birth, regardless of confounding factors, according to a study by Florent Fuchs from CHU Sainte Justine, Canada and colleagues.

Maternal age at pregnancy has been increasing worldwide and so has the risk for preterm birth. However, the association between maternal age and preterm birth remains a topic of ongoing research.

Fuchs and colleagues sought to investigate the impact of maternal age on preterm birth in a large cohort. The researchers analysed the previously-collected data from the QUARISMA randomised controlled trial, which had taken place in 32 hospitals in Quebec, Canada, from 2008 to 2011.

The researchers identified five different age groups among the 165,282 pregnancies included in the study, and compared them based on maternal characteristics, gestational and obstetric complications, and risk factors for prematurity. Some of the known risk factors identified more commonly in older mothers (40 and over) included placental praevia, gestational diabetes, medical history, use of assisted reproduction technologies and occurrence of an invasive procedure. On the other hand, nulliparity, past drug use and smoking were more prevalent in younger mothers (30 and under).

Even after adjusting for confounding factors, the researchers found that advanced maternal age (40 or over) was associated with preterm birth. Meanwhile, a maternal age of 30–34 years was associated with the lowest risk of prematurity.

Abstract
Background: Maternal age at pregnancy is increasing worldwide as well as preterm birth. However, the association between prematurity and advanced maternal age remains controversial.
Objective: To evaluate the impact of maternal age on the occurrence of preterm birth after controlling for multiple known confounders in a large birth cohort.
Study design: Retrospective cohort study using data from the QUARISMA study, a large Canadian randomized controlled trial, which collected data from 184,000 births in 32 hospitals. Inclusion criteria were maternal age over 20 years. Exclusion criteria were multiple pregnancy, fetal malformation and intra-uterine fetal death. Five maternal age categories were defined and compared for maternal characteristics, gestational and obstetric complications, and risk factors for prematurity. Risk factors for preterm birth <37 weeks, either spontaneous or iatrogenic, were evaluated for different age groups using multivariate logistic regression.
Results: 165,282 births were included in the study. Chronic hypertension, assisted reproduction techniques, pre-gestational diabetes, invasive procedure in pregnancy, gestational diabetes and placenta praevia were linearly associated with increasing maternal age whereas hypertensive disorders of pregnancy followed a “U” shaped distribution according to maternal age. Crude rates of preterm birth before 37 weeks followed a “U” shaped curve with a nadir at 5.7% for the group of 30–34 years. In multivariate analysis, the adjusted odds ratio (aOR) of prematurity stratified by age group followed a “U” shaped distribution with an aOR of 1.08 (95%CI; 1.01–1.15) for 20–24 years, and 1.20 (95% CI; 1.06–1.36) for 40 years and older. Confounders found to have the greatest impact were placenta praevia, hypertensive complications, and maternal medical history.
Conclusion: Even after adjustment for confounders, advanced maternal age (40 years and over) was associated with preterm birth. A maternal age of 30–34 years was associated with the lowest risk of prematurity.

Authors
Florent Fuchs, Barbara Monet, Thierry Ducruet, Nils Chaillet, Francois Audibert

PLOS One abstract

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