Changes in Multiple Birth Rates and Parental Demographic Factors in South Korea During the Last Four Decades: 1981-2019

Genetic and Environmental Influences on Perceived Stress in South Korean Twins

Researchers have proposed that culture significantly influences perceived stress (PS). To date, however, twin studies on PS have been conducted mostly in western, individualistic cultures, which demonstrate that PS due to controllable (personal) life events is more heritable than PS due to uncontrollable (network) life events. This study aimed to investigate genetic and environmental influences on PS in South Korean twins. South Korea practices a dominant collectivist culture. In total, 1372 twin individuals (mean age = 22.4 ± 2.5 years) completed an online survey on PS, which consisted of the scales, Friendship, Academic Stress, Future Career, Family Conflicts, and Family Financial Difficulties (FFD). Friendship, Academic Stress, and Future Career can be considered PS due to personal life events, and Family Conflict and FFD, PS due to network life events. The general sex-limitation model-fitting analysis revealed the absence of qualitative or quantitative sex differences in genetic and environmental influences. Specifically, additive genetic influences were predominant for Friendship (63%), Academic Stress (67%), and Future Career (57%) for both sexes, with the remaining variance attributable to nonshared environmental influences. In contrast, shared environmental influences were largest for Family Conflict (47% for both genders) and FFD (64% for males, 63% for females) with no significant genetic effects. Despite known cultural differences in the means and variances of PS, South Korean twins exhibited significant genetic effects in PS due to personal life events and large shared environmental effects in PS due to network life events, which is similar to western samples.

The impact of assisted reproductive technology treatment coverage on marriage, pregnancy, and childbirth in women of childbearing age: an interrupted time-series analysis

BACKGROUND

Korea is encountering major challenges related to its declining birth rate and aging population. Various policies have been introduced to prevent further population decrease and boost the birth rate, but their effectiveness has not been verified. Therefore, this study examined the effects of assisted reproductive technology (ART) insurance coverage on marriage, pregnancy, and childbirth in women of childbearing age.

METHODS

All information on marriage, pregnancy, childbirth of women of childbearing age was obtained from Statistics Korea and Korean National Health Insurance Service database. During a total follow-up period of 54 months (July 2015 to December 2019), an average of 12,524,214 women of childbearing age per month, and 29,701 live births per month were included in the analysis. An interrupted time series with segmented regression was performed to analyze the time trend and changes in outcomes.

RESULTS

The implementation of ART coverage policies had no significant impact on marriage or pregnancy rates. However, it did affect multiple pregnancy and multiple birth rates, which increased by 1.0% (Exp(β3) = 1.010, P-value = 0.0001) and 1.4% (Exp(β3) = 1.014, P-value = < 0.0001), respectively, compared to the pre-intervention period. Although the effect of covering ART treatment on total birth rates were not confirmed, a slightly slower decline was observed after the intervention (Exp(β1) = 0.993, P-value = < 0.0001, Exp(β1 + β3) = 0.996 P-value = 0.012).

CONCLUSION

This study identified the effects of ART health insurance coverage policy on the rates of multiple pregnancies and births. After the policy implementation, the downward trend in the total birth rate reduced slightly. Our findings suggest that interventions to support infertile couples should be expanded to solve the problem of low fertility rates. To address the intricate problems related to low birth rates, the Korean government introduced a policy that provides financial support and health insurance coverage for assisted reproductive technology (ART) treatment for infertile couples. As a result of evaluating the effectiveness of the ART coverage policy, it led to higher rates of pregnancies and births. In addition, although the total birth rate has been continuously decreasing over time, the decline may have been slowed down slightly by this policy.

Secular Trends of Birth Weight in Twins and Singletons in South Korea from 2000 to 2020

Whether the decline of birth weight (BW) reported in developed countries in the early 2000s is ongoing remains unknown. Furthermore, despite recent sharp increases in twin births, comparing secular trends of BW between singletons and twins is difficult, as studies have rarely examined secular trends of BW in twins and singletons simultaneously. Therefore, this study aimed to investigate the most recent 20-year trends (2000-2020) of BW in twins and singletons in South Korea. Annual natality files from 2000 to 2020 obtained from the Korean Statistical Information Service were analyzed. A yearly decrease of BW was 3 g among singletons and 5 to 6 g in twins from 2000 to 2020, indicating a widening gap of BW between twins and singletons with increasing years. Gestational age (GA) also decreased in twins and singletons with yearly decreases of 0.28 days in singletons and 0.41 days in twins. Whereas BW decreased in term (GA ≥ 37 weeks), and very preterm groups (28 weeks ≤ GA < 32 weeks) from 2000 to 2020 in twins and singletons, it increased in moderate to late preterm (32 weeks ≤ GA < 37 weeks) groups, indicating a non-linear relationship between BW and GA. The prevalence of macrosomia (BW > 4000 g) in singletons decreased from 2000 to 2020, whereas low birth weight (LBW; BW < 2500 g) increased in twins and singletons. LBW is associated with adverse health outcomes. Effective public health strategies aiming at reduction in the incidence of LBW in the population should be developed.

Effects of assisted reproductive technology on severe maternal morbidity risk in both singleton and multiple births in Korea: A nationwide population-based cohort study

BACKGROUND

Whether infertility treatment predicts severe maternal morbidity in both singleton and twin pregnancies is controversial. We conducted this nationwide population-based cohort study to compare pregnancies conceived through assisted reproductive technology treatments, such as intrauterine insemination or in vitro fertilization, with unassisted pregnancies.

METHODS

This study included 269,930 women who experienced childbirth in 2018, using data of the National Health Insurance Service National Delivery Cohort in Korea. The primary outcome was assessed using a severe maternal morbidity algorithm developed by the Centers for Disease Control and Prevention in the United States. A modified Poisson regression was used to estimate the adjusted risk ratio of severe maternal morbidity.

RESULTS

Severe maternal morbidity occurred in 6,333 (2.3%) of 280,612 deliveries investigated. The risk of severe maternal morbidity was approximately 1.5-fold higher among women who received in vitro fertilization (risk ratio: 1.51, 95% confidence interval: 1.36-1.68) than among fertile women. However, no significant association between intrauterine insemination and maternal morbidity was identified. Via subgroup analysis, in vitro fertilization increased the risk of severe maternal morbidity by 1.6- and 1.3-fold in singleton and multiple births, respectively (singleton: risk ratio: 1.62, 95% confidence interval: 1.43-1.83; multiple birth: risk ratio: 1.31, 95% confidence interval: 1.07-1.60).

CONCLUSIONS

This study suggested that in vitro fertilization was associated with the risk of severe maternal morbidity in both singleton and multiple births. Further research should identify patient- and treatment-specific factors that may mitigate or prevent adverse maternal health risks.

Temporal trends and adverse perinatal outcomes of twin pregnancies at differing gestational ages: an observational study from China between 2012–2020

Background

With the development of assisted reproductive technology, the twinning rate in China has been increasing. However, little is known about twinning from 2014 onwards. In addition, previous studies analysing optimal gestational times have rarely considered maternal health conditions. Therefore, whether maternal health conditions affect the optimal gestational time remains unclear.

Methods

Data of women delivered between January 2012 and December 2020 were collected through China’s National Maternal Near Miss Surveillance System. Interrupted time series analysis was used to determine the rates of twinning, stillbirth, smaller than gestational age (SGA), and low Apgar scores (< 4) among twins in China. To estimate the risk of each adverse perinatal outcome for separate gestational weeks, a multivariate generalised linear model was used. Infants born at 37 weeks of gestational age or foetuses staying in utero were used as reference separately. The analyses were adjusted for the sampling distribution of the population and the cluster effect at the hospital and individual levels were considered.

Results

There were 442,268 infants enrolled in this study, and the adjusted rates for twinning, stillbirth, SGA, and low Apgar scores were 3.10%, 1.75%, 7.70%, and 0.79%, respectively. From 2012 to 2020, the twinning rate showed an increasing trend. Adverse perinatal outcomes, including stillbirth, SGA, and low Apgar scores showed a decreasing trend. A gestational age between 34 and 36 weeks decreased most for rate of stillbirth (average changing rate -9.72%, 95% confidence interval [CI] -11.41% to -8.00%); and a gestational age of between 37 and 38 weeks decreased most for rates of SGA (average changing rate -4.64%, 95% CI -5.42% to -3.85%) and low Apgar scores (average changing rate -17.61%, 95% CI -21.73% to -13.26%). No significant difference in changes in twinning rate or changes of each perinatal outcome was observed during periods of different fertility policies. Infants born at 37 weeks of gestation had a decreased risk of stillbirth, SGA, and low Apgar scores. Maternal antepartum or medical complications increased the risk of SGA and low Apgar scores in different gestational weeks.

Conclusion

China’s twinning rate showed an increasing trend, while adverse perinatal outcomes decreased from 2012 to 2020. Fertility policy changes have had little effect on the twinning rate or the rate of adverse perinatal outcomes such as stillbirth, SGA, or low Apgar scores. The optimal gestational age for twins was 37 weeks. Women pregnant with twins and with antepartum or medical complications should be cautious due to an increased risk of SGA and low Apgar scores.

Twinning rates in Chennai, India – A cross-sectional study

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