The impact of parity and age at first and last childbirth on the prevalence of delayed-onset asthma in women: The Korean National Health and Nutrition Examination Survey

Highlights

• Korean women aged under 20 years at first childbirth were significantly more likely to experience delayed-onset asthma.

• Higher parity showed a tendency toward correlation with the prevalence of delayed-onset asthma.

• This general population-based study on the prevalence, risk factors, and comorbidities of asthma will contribute to the prevention and management of asthma and its comorbidities among Korean individuals.

Abstract

Object

Asthma is a chronic inflammatory airway disease. The aim of this study was to investigate the relationships between asthma and reproductive factors, including age at first childbirth and parity, in a representative sample of Korean women.

Main outcome measures

We analyzed data from the Korean National Health and Nutrition Examination Survey (2010–2012). A total of 7837 adults who completed a questionnaire and examination were evaluated. The presence of asthma was based on the Health Interview Survey. Reproductive factors were estimated by trained interviewers using participant recall.

Results

The women with asthma were significantly older than those without asthma. BMI, hypertension, education level, income level, occupation, alcohol consumption, and age at menarche and first birth were significantly associated with the diagnosis of asthma. Higher parity was positively associated with later-onset asthma. In addition, women who were younger at first birth had a greater prevalence of later-onset asthma. After controlling for confounders, being aged under 20 at first birth was significantly associated with an asthma diagnosis compared with women aged 25–29 at first birth (OR [95% CI]: 1.81 [1.14–2.89]).

Conclusions

Although higher parity was associated with asthma in women, its significance disappeared after adjustment. These results warrant future studies to explore the mechanisms responsible for the association between reproductive factors and asthma.

Introduction

Asthma is an inflammatory disorder of the airway and lung tissue that varies in nature and severity over time. A core feature of asthma is the presence of airway hyper-responsiveness, a condition in which individuals respond to non-allergic stimuli (e.g., cigarette smoke and fog) with airway obstruction, wheezing, and other respiratory symptoms that do not occur in healthy individuals [1]. There has been a sharp increase in the global prevalence, morbidity, mortality, and economic burden associated with asthma over the past 40 years. Many epidemiologic studies suggest the presence of gender differences in asthma prevalence and severity vary according to age. The prevalence of asthma is higher among males during childhood, approximately equal in both sexes during teenage years, and higher among females during adulthood [2]. Although, large epidemiologic studies investigating menopause and asthma are scarce and show contradictory results [3], recent several studies pointed to a higher asthma prevalence in post-menopause [4], [5]. Furthermore, the number of respiratory symptoms was higher in women who were postmenopausal at follow-up [6]. In addition, asthma severity has been found to vary during the menstrual cycle and pregnancy. These findings suggest that reproductive hormones influence the development of asthma and asthma severity [7].

There have been several studies which aimed to verify the association between reproductive factors, particularly hormone exposure, and the prevalence or severity of asthma among women. However, the associations between these factors remain controversial. Women with early menarche and pregnancy have higher estrogen levels and are exposed to greater cumulative estrogen and progesterone concentrations [7]. One study reported that bronchial hyper-responsiveness, a key feature of asthma, was significantly associated with early menarche [8]. Another study found that early menarche, before 11 years of age, was not associated with an increased risk of wheezing during adolescence [9]. Similarly, Jenkins et al. reported that the risk of later-onset asthma among women with no asthma by age seven was associated with increased parity [2], but others found that women with greater numbers of intervening pregnancies were more likely to have lost their atopic status and did not observe any relationship between pregnancy and current symptoms of asthma [10], [11]. Nevertheless, these data on the pattern of asthma according to sex hormonal status has been limited to local communities or particular age groups; population-based studies on the relationship between asthma and these factors are lacking. It is important to recognize the factors associated with asthma and its etiology in order to prevent possible complications. The aim of this study was to analyze the prevalence of asthma and its potential risk factors, including menarche, parity, and timing of first or last pregnancy using KNHANES data, a government-driven survey of the Korea Center for Disease Control and Prevention.