Contribution of Maternal Age Distribution to Incidence of Preterm Birth; 1997~99 and 2012~14 Singleton Birth Certificated Data of Korea

Park,  Sang Hwa; Kim,  Hoon; Lim,  Dar Oh

doi:2016.20.3.221

J Korean Soc Matern Child Health > Volume 20(3); 2016 > Article

Journal of The Korean Society of Maternal and Child Health 2016;20(3):221-227.
DOI: https://doi.org/10.21896/jksmch.2016.20.3.221 Published online September 30, 2016.

Contribution of Maternal Age Distribution to Incidence of Preterm Birth; 1997~99 and 2012~14 Singleton Birth Certificated Data of Korea

Sang Hwa Park¹, Hoon Kim², Dar Oh Lim³

¹Institute of Reproductive Medicine and Population, Medical Research Center, Korea
²Department of Obstetrics and Gynecology, College of Medicine, Seoul National University, Korea
³Department of Health Administration, Kongju National University, Korea

출산 연령 구조가 조기분만율에 미치는 기여효과: 단태아 출생통계 중심으로, 1997~99, 2012~14

박상화¹, 김훈², 임달오³

¹서울대학교 의학연구원 인구의학연구소
²서울대학교 의과대학 산부인과학교실
³공주대학교 보건행정학과

Correspondence: Dar Oh Lim,
Email: moon5@kongju.ac.kr

Abstract

Purpose
The objective of the study was to compare contribution of maternal age to preterm birth (PTB) rates between 1997~99 and 2012~14.
Methods
We used 1997~99 (1,872,720 births) and 2012~14 (1,280,348 births) singleton birth certificated data of Korea Statistics excluding multiple birth and extra-marital birth cases. We decomposed the contributions of age-specific PTB rates and maternal age distribution (Kitagawa’s decomposition method) to overall PTB rates during the period. Odds ratio (OR) and 95% confidence intervals were calculated from logistic regression to describe the secular trend of PTB rate by birth year and maternal age.
Results
The incidence of PTB increased 1.5 times, from 3.0 percent to 4.6 percent, during 1997~ 2014. After adjustment by logistic regression for infantile sex, parity and maternal age, the odds ratio of PTB in birth year of 2012~14 was 1.38 (95% confidence interval: 1.36~1.39), compared with incidence of PTB in 1997~99. During the period, PTB rates increased 1.79 times in women aged 20~24 years and 25~29 years (OR: 1.56), whereas rates remained stable in women aged 35 years and older (OR: range from 1.08 to 1.13). 87.5% of the overall increase in the PTB rates was attributable to the increase in the proportion of women aged 30~34 years, but these age group accounted for only a small portion of the increase in PTB rates (OR: 1.27).
Conclusion
The remainder of the total increment in the PTB rates during the period was explained by increase the proportion of women aged 30~34 years. There was a need to close attention in this area to understand the contributing factors to the secular trend of PTB rates.

Key Words: singleton preterm birth, maternal age, contribution of preterm