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The Korea Nurses' Health Study (KNHS)
The Korea Nurses’ Health Study (KNHS) which began in July 2013 in collaboration with the Korean Nurses Association (KNA) and Harvard University, is a prospective cohort study of female nurses that investigated the effects of occupational, environmental, and lifestyle risk factors on the health of Korean women. Female registered nurses aged 20–45 years and living in Korea were invited to join the study and asked to complete a web-based baseline survey in the four different modules at 6-month intervals. The study protocols and questionnaires related to the KNHS were based on the Nurses’ Health Study 3 (NHS3), which is used in the United States, although they were modified to reflect the Korean lifestyle. Participants were asked about demographic and lifestyle factors, disease history, occupational exposure, reproductive factors, dietary habits, and diet during their adolescence. If a participant became pregnant, she was asked to answer additional questionnaires requesting pregnancy-related information. The baseline survey (Module 1) was closed in October 2014, and 20,613 nurses aged 20–45 years completed the web-based selfadministered questionnaires. Modules 2 and 3 began in March and November 2014, respectively, and Module 4 began in September 2015. Two additional modules for early-pregnancy and postpregnancy (Modules 5 and 6) were sent to participants who become pregnant after July 2014. Data from Modules 2–4 and the pregnancy modules are under investigation. The KNHS is the first cohort study to focus on working Korean women of reproductive age and as such, it provides an opportunity for young nurses to participate in a long-term prospective study. As the KNHS survey items were basically matched to those in the US NHS3, the findings from both data sets offer the chance to compare risk exposure in terms of ethnic and environmental differences.
Prospective Observational Study of Pregnant Women
To investigate the prevalence and risk factors of pregnancy complications among Korean pregnant women, a prospective observational study was started in 2013 in collaboration with the Cheil General Hospital and CHA Gangnam Medical Center located in Seoul. We focused on gestational diabetes, gestational hypertension, and postpartum depression, known as relatively serious and common complications occurring with pregnancy. Pregnant women around 12 weeks of gestation were enrolled in this registry when visiting the hospital. A structured questionnaire was used to collect information about the following areas: demographics (marital status, family type/number of family members, occupational status, income, and education), lifestyle factors (smoking, drinking, and physical activity), psychological status (distress thermometer score, marital satisfaction, and quality of life), and dietary intake (dietary habit and food intake). More than 3,500 pregnant women were enrolled and about 47,000 sample vials (plasma, DNA, tissue) were collected from March 2013 to December 2015. Total deliveries were 2,152 during the same period.
Prospective Observational Study of Perimenopausal Women
A prospective observational study of perimenopausal women was established in 2014 to investigate the risk factors for physical and mental disorders during menopausal transition. Together with the health promotion center at Kangbuk Samsung Hospital in Seoul, participants were enrolled and a standard questionnaire was completed. Data and biological samples (urine and blood)of participants were collected from the medical examination at the time of a health check-up. Baseline eligibility criteria included the following: 42-52 years of age, having one or more menstrual cycles in the previous 3 months, not undergoing hormone replacement therapy, presence of an intact uterus and at least one ovary, no history of cancer, no use of contraceptive pills over the last 10 menstrual cycles, and no renal failure, hyperthyreosis or hypothyroidism, or use of medication in the previous year. The standard questionnaire, which included the menopausal status of subjects and Menopause-Specific Quality of Life Questionnaire (MENQOL), was used to assess the participants’ menopausal experience. Clinical data and biological samples for about 3,350 premenopausal women were collected from April 2014 to December 2015. A subsequent followup study at early and late menopausal transition and postmenopause is being analyzed.
Korean Neonatal Network (KNN)
The Korean Neonatal Network (KNN), a national multicenter neonatal network based on a prospective web-based registry for very-low-birth-weight (VLBW) infants (<1,500 g), was officially started in 2013 for the first time in Korea. In collaboration with the Korean Society of Neonatology, the KNN collected clinical data annually on more than 2,000 VLBW infants from the neonatal intensive care unit (NICU) of 64 participating hospitals throughout the country, covering about 70% of the overall admissions of VLBW infants born in Korea at present. VLBW infants admitted to the NICU at birth or transferred from other hospitals within 28 days of life to the KNN-participating hospitals are registered to the KNN registry (visit 1). Then, long-term outpatient follow-up at 18-24 months (visit 2) and 3 years of age (visit 3) are discharged. Through a unique system of web-based simultaneous data display on its homepage and site-visit monitoring for data quality surveillance, more than 6,000 VLBW infants were enrolled in the KNN registry and about 820 infants were followed by December 2015. Furthermore, KNIH and the KNN executive committee have published an annual report of data for the total registered cases born in the previous year, providing objective evidence of the status of a NICU in relation to all other NICUs participating in the KNN in terms of patient characteristics, treatment policies, care quality, and patient outcomes. The KNN will facilitate active multicenter neonatal research to improve the survival rate and decrease the complication rate of high-risk newborn infants and will ultimately lead to an improvement in the prognosis of high-risk newborn care in Korea through the development of evidence-based medicine.
Study of Health Conditions Specific to Women
Although the prevalence of hypertension is higher in postmenopausal women than in premenopausal women, little is known about changes in blood pressure (BP) during the menopausal transition. We evaluated BP according to the menopausal transition and associated factors in healthy Korean women, using the cross-sectional study involving 2,037 women aged 44-56 years who presented at a health-screening center in Seoul, Korea, from November 2012 to March 2013. Menopausal status was divided into four groups as premenopause, early menopausal transition, late menopausal transition, and postmenopause. Both systolic and diastolic blood pressure (SBP and DBP) differed significantly according to the menopausal status. BP showed the greatest difference between early and late menopausal transition. After adjusting for variables related to hypertension, SBP (β = 2.753, p < 0.01) and DBP (β = 1.746, p = 0.02) were significantly higher in late compared to early menopausal transition. The prevalence of hypertension was significantly different between early and late menopausal transition (1.4 vs. 6.1%). Waist circumference, glucose, and triglycerides were positively and significantly associated with SBP and DBP during menopause. These findings suggest that changes in BP during the menopausal transition are significant; therefore, frequent monitoring will be needed for early detection of hypertension during the menopausal transition.
Gestational diabetes mellitus is associated with maternal morbidity and complications such as pre-eclampsia, premature rupture of membranes, and Caesarean section. In Korea, rates of gestational diabetes and pre-existing diabetes have recently been increasing, but few studies have evaluated these diseases specifically in Korean females. We evaluated the effects of gestational diabetes and pre-existing diabetes on maternal morbidity and medical costs, using data from the Korea National Health Insurance Claims Database of the Health Insurance Review and Assessment Service. Although, the rates of pre-existing diabetes did not fluctuate (2.5, 2.4, and 2.7%), the rate of gestational diabetes steadily increased (4.6, 6.2, and 8.0%). Furthermore, the rates of pre-existing diabetes and gestational diabetes increased in conjunction with maternal age, pre-existing hypertension, and cases of multiple pregnancy. The risk of pregnancy-induced hypertension, urinary tract infections, premature delivery, liver disease, and chronic renal disease were greater in the gestational diabetes and pre-existing diabetes groups than in the normal group. The risk of venous thromboembolism, antepartum hemorrhage, shoulder dystocia, and placenta disorder were greater in the pre-existing diabetes group, but not the gestational diabetes group, compared with the normal group. The medical costs associated with delivery, the costs during pregnancy, and the number of in-hospital days for the subjects in the pre-existing diabetes group were the highest among the three groups. The study showed that the rates of pre-existing diabetes and gestational diabetes increased with maternal age at pregnancy and were associated with increases in medical costs and pregnancy-related complications.