J Korean Soc Matern Child Health.  2017 May;21(2):112-118. 10.21896/jksmch.2017.21.2.112.

Length of First Birth Interval and Incidence of Twin Birth in Korea; 2010~2015

• Park SH
• Lim DO

• KMID: 2449570
• DOI: http://doi.org/10.21896/jksmch.2017.21.2.112

Abstract

PURPOSE
To compare the incidence of twin births with the length of first birth interval (LFBI: from marriage to first birth) among primiparous women.
METHODS
The birth certificated data of Korea Statistics from 2010 to 2015 were used for this analysis. There were 1,356,204 births of primiparous women from total birth cases (2,736,296 births). The data involving multiparous women, teenage birth, extra-marital birth, and triplet birth cases were excluded from all analyses. Odds ratio and 95 percent confidence intervals were calculated from logistic regression to examine the risk of twin birth by LFBI adjusted for year of birth, maternal age, paternal age, age difference between couples, and maternal education and occupation.
RESULTS
The frequency of LFBI was 41.5 percent in ≤12 months, 30.7 percent in 13~24 months, 13.1 percent in 25~36 months, and 2.1 percent in LFBI of ≥85 months. The mean LFBI was 21.5 months. The incidence of twin birth increased with prolonged LFBI. The twin birth rates per LFBI were 0.8 percent, 3.1 percent, 7.9 percent, and 11.0 percent in LFBI of ≤12 months, 25~36 months, 49~60 months, and 73~84 months, respectively. Odds ratio of twin births rate by LFBI were 1.510 (95% confidence interval: 1.449~1.574) for the LFBI of 13~24 months, 9.839 (9.390~10.309) for 49~60 months, and 13.244 (12.458~14.080) for ≥73~84 months, each compared with LFBI of ≤12 months. Odds ratio of twin birth rate in LFBI of ≤72 months was higher in women aged 35 and older, as compared to women aged ≤34 years. Odds ratio of twin birth rate by maternal age (≤34 years versus ≥35 years) reversed in LFBI of ≥73 months.
CONCLUSION
The risk of twin birth increased significantly with prolonged LFBI. There is a need to understand the factors (fertility therapy and etc.) to increased risk of twin birth in prolonged LFBI.

Keyword

first birth interval; twin birth; prolonged LFBI

MeSH Terms

Birth Intervals*
Birth Order*
Birth Rate
Education
Family Characteristics
Female
Humans
Incidence*
Korea*
Logistic Models
Marriage
Maternal Age
Occupations
Odds Ratio
Parturition*
Paternal Age
Triplets
Twins*