Risk Factors of Preterm Delivery in Pregnant Women Aged 35 Years or Older: Analysis of Birth Certificate Data in 1996

Park, S H; Han, J H; Kim, S M; Koo, S Y; Kim, S H

Abstract

OBJECTIVE
This study was performed to investigate the risk factors of preterm delivery in nulli- and multiparous women aged 35 years or older.
METHODS
A total of 34,342 singleton birth cases from the birth certificate data in the year of 1996 obtained from the National Statistical Office of Korea was reviewed and analyzed. The logistic regression analysis was used to examine the relationship between preterm delivery and risk factors including infantile sex, maternal age and parity, age difference between couples, education level, and season of birth.
RESULTS
The sex ratio in newborns was 127.5[19,244/15,098]. The rates of low birth weight and preterm delivery were 4.8%[1,643/34,342] and 5.0%[1,697/34,220], respectively. The parity of women aged 35 years or older was 24.2% in the nulliparous and 75.8% in the multiparous. The season of birth was 24.7% in spring, 23.7% in summer, 25.5% in autumn, and 26.1% in winter. The risk for preterm delivery was significantly higher in the nulliparous women aged 40 years or older, compared with the multiparous women aged 35-39 years[odds ratio[OR]: 1.54, 95% confidence interval[CI]: 1.21-1.95, p<0.001]. This risk was significantly higher in spring[OR: 1.19, p<0.05], summer[OR: 1.23, p<0.01], and autumn[OR: 1.34, p<0.001], compared with winter. However, there was no significant association between the preterm delivery and the other clinical factors such as newborn sex, parents` education level, and age difference between couples.
CONCLUSION
Maternal older age and nulliparity can be considered as the risk factors for preterm delivery.