pairs), provided by Statistics Korea. Weinberg's differential rule was used to estimate the number of MZ and DZ twin births. The impact of assisted reproductive technologies (ART) on MZ and DZ twinning was analyzed by examining data after the introduction of the national support program for infertile couples. The odds ratio (OR) and 95% confidence intervals were calculated to describe the trend in the MZ and DZ twinning ratio. Results: From 1991 to 2018, the DZ/MZ ratio increased significantly from 0.45 to 3.30. Prior to the introduction of the national support program for infertile couples (1991-1994 years), the DZ/MZ ratio was 0.54, but after its introduction, the DZ/MZ ratio was 1.

Background: International comparison and time trend surveillance of preterm delivery rates is complex. New techniques that could facilitate interpretation of such rates are needed.

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Objectives: To compare contribution of age distribution and age specific death rates to intentional self-harm (ISH) between 1985-89 and 2010-14. Methods: We used 1985-89 (16,977 deaths) and 2010 ISH death data of Korea Statistics. We decomposed the contributions of agespecific ISH death rates and age distribution of population (Kitagawa's decomposition method) to overall increment of ISH death rates during the period. Odds ratio (OR) and 95% confidence intervals were calculated to describe the secular trend of ISH death rates by age groups. Results: Between 1985-89 and 2010-14, ISH death rates (per 100,000 persons) increased from 8.16 to 29.57 (OR: 3.62, 95% confidence interval: 3.56-3.86). ISH death rates increased from 11.74 to 40.45 in male (OR: 3.44) and increased from 4.53 to 18.66 in female (OR: 4.12). ISH death rates have risen with advancing age, peaking at 60 years & older in both gender. In 1985-2014, a prominent increase in ISH death rates occurred among those aged 60 years and older (3.82 times in male, and 4.28 times in female), and followed by the group of 40-59 years (2.81 times in male, and 3.54 times in female). Most (59.6 percent) of the overall increase in the ISH death rates was attributable to male age group of 40-59 years and 60 years & older, and 25.3 percent of the overall increase of death rates was attributable to female age group of 40 years & older. Conclusions: The remainder of the total increment in the ISH death rates during the period was explained by increase the proportion and the excessive death rates of male age group of 40-59 years and 60 years & older. There was a need to close attention in male age group of 40 years & older to reduce ISH death rates and understand the contributing factors to ISH death.

To determine the secular trend of the multiple birth rate in Korea from 1981 to 2017. Methods: This study used birth certificate data covering the years 1981-2017 (20,948,901 births), provided by Statistics Korea. The impact of assisted reproductive technologies (ART) on multiple birth was analyzed by examining data prior to and after the introduction of ART and the national support program for infertile couples in South Korea. The odds ratio (OR) and 95% confidence intervals were calculated to describe the secular trend in the multiple birth rate per 100 births. Results: During this period, the multiple birth rate per 100 births increased by 277 percent from 1.031 to 3.891, the twin birth rate increased from 1.013 to 3.807 (275%), and the triplet birth rate increased from 0.018 to 0.084 (363%). The secular trend of the multiple birth rate remained in the 1.000 level during 1981-1991, but has been rising steadily since 1992. The average increment of the multiple birth rate was