Objectives: The objective of the study was to analyze the secular trend of late preterm birth (LPT: 34-36 weeks) by analyzing birth certificated data (1995: 713,038, 2000: 632,440, 2005: 430,662, 2010: 468,607, 2012: 484,052) of Korea Statistics.
Methods: Odds ratio and 95% confidence intervals were calculated from logistic regression analyses to describe the secular trend (1995-2012) of LPT adjusted for infantile sex, birth order, number of fetus, maternal age, maternal education &
occupation, and marital status (marital & extra-marital birth).
Results: The incidence of infants born LPT rose 2.6 times, from 1.9 percent to 4.9 percent, during 1995-2012. The mean gestational age decreased from 39.67 weeks in 1995 to 38.63 weeks in 2012. After adjustment by logistic regression for infantile sex, birth order, number of fetus, maternal age, maternal education & occupation, and marital status (marital & extra-marital birth), the odds ratio of LPT in birth year of 2000, 2005, 2010 and 2012 were, respectively, 1.57 (95% confidence interval: 1.54-1.61), 1.99 (1.94-2.04), 2.44 (2.38-2.50), and 2.52 (2.46-2.58), compared with incidence of LPT in 1995. Between 1995 and 2012, the rate of increase in LPT was higher in marital birth (vs. extra-marital birth), in multiple birth (vs. singleton birth), and in maternal age at ＜ 35 years (vs ≥ 35 years).
Conclusions: The possible contributing factors to the rising LPT rate included advanced maternal age, artificial eproductive technologies, multiple births, and extra-marital birth. There was a need to more research in this area to understand the contributing risk factors for increasing LPT.
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