Preterm Birth and Low Birth Weight in Extramarital Birth in Korea: 2015-2018 Years

Objectives: The purpose of this study was to analyze the risk of preterm birth (PTB) and low birth weight (LBW) in babies born to unmarried parents (extramarital birth). Methods: This study used birth certificate data (1,523,594 births) from Korea Statistics, 2015-2018 years. Odds ratio and 95% confidence intervals were calculated by logistic regression analyses to describe the risk of PTB and LBW in extramarital birth adjusted for maternal age, maternal education, infantile sex, and type of birth (singleton & multiple birth). Results: During this periods, the rate of extramarital birth was 1.9 percent in 2015-2018. The incidence of LBW was 8.4 percent in extramarital birth and 5.9 percent in marital birth. The rate of PTB in extramarital birth were 10.6 percent and 7.3 percent in marital birth. The LBW and PTB rate of extramarital birth (father listed on the birth certificate) was 7.4 percent and 9.1 percent, respectively. Among extramarital birth (father not listed on the birth certificate) was associated with increased risk of PTB (12.3%) and LBW (9.5%). Compared with LBW and PTB rate of marital birth, the odds ratio (OR) for LBW and PTB were 1.66 (95% confidence interval, 95% CI: 1.56-1.77) and 1.57 (95% CI: 1.49-1.67) for extramarital birth (father listed). Risk of LBW (OR: 2.14) and PTB (OR: 2.14) was higher in extramarital birth (father not listed) than that of marital birth. Conclusions: The babies born to unmarried parents was associated with increased risk of LBW and PTB, compared with those of marital birth. Risk of adversed pregnancy outcome was higher in extramarital birth (father not listed on the birth certificate). More study is required to understand the factors to adversed pregnancy outcome of extramarital status.