Working women or dual-income households in South Korea have fewer children on average than households with a single breadwinner, as child care is disproportionately also done by women, reports showed Monday.

Based on household surveys of partners aged 25 to 44, dual-income households had an average of 1.36 children while single-income households had 1.46 children last year, according to Statistics Korea's study of fertility disparities based on economic and social factors.

Elite families with a single breadwinner had the most children on average, according to the study. Single-income families in the top quintile income bracket had an average of 1.75 children, whereas dual-income households in the same bracket had 1.43 children.

However, families in the lowest quintile income bracket showed different aspects, with households in which both partners were employed having slightly more children -- 1.42 -- than those with just one income -- 1.35.

“Low-income households may have a higher number of children in dual-income households because they are more likely to be unable to use parental leave to care for children and give birth due to financial reasons,” the report said.

The report also showed a negative correlation between women's incomes and the number of children they had on average. When women's incomes increased by 100 percent, the number of children they had decreased by 4 percent.

Women having an income correlated to a 5-percent lower probability of having children, while men having an income correlated to a 6-percent higher probability of having children.

The Korea Development Institute also released a report last month that found that the increase in workplace disadvantages associated with career interruptions accounts for about 40 percent of the reason for the decline in the birth rate between 2013 and 2019.

According to the Organization for Economic Cooperation and Development and the KDI, the ratio of men's to women's unpaid work hours, which refers to men's participation in domestic labor, is 23. The OECD average is 52, more than double that of South Korea's men.

The report criticized Korea's reality where women face delays in promotion after marriage and childbirth, as well as unfair distributions of household responsibilities, which contribute significantly to the low birth rate.

"Many young women witness their peers encountering promotion delays after marriage and childbirth, dealing with problems in sharing housework responsibilities and having difficulty finding adequate child care," the report stated.

The IMF has recommended supporting women's employment and career growth opportunities by promoting career flexibility. It also suggested increasing male participation in child care by providing more incentives for husbands to take paternity leave, according to the report.