Frequency of sexual intercourse tends to be lower among Japanese couples compared to couples overseas, or are having more extramarital sex

Proximate Determinants of Fertility in Japan. Shoko Konishi, Emi Tamaki.. Biodemography of Fertility in Japan pp 13-42, https://link.springer.com/chapter/10.1007/978-981-10-0176-5_2

Abstract: Proximate determinants link both social and biological factors to fertility. In this section, we will summarize available data related to proximate determinants of fertility in Japan while referring to some of the related literature targeting populations overseas. In addition to data from published studies, we present our original data collected in the biodemography project, an Internet-based cross-sectional survey on reproductive history conducted in 2014 targeting Japanese women between 20 and 44 years of age. Following Wood’s conceptualization, the specific components of the proximate determinants of fertility referred to in this chapter are lactational infecundability, fecund waiting time to conception, and fetal loss (both spontaneous and induced). Additionally, papers on factors that are expected to significantly affect fecund waiting time to conception, i.e., frequency of sexual intercourse, length and regularity of menstrual cycle, and use of contraception and infertility treatment, will be reviewed.

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Recent research suggests that frequency of sexual intercourse tends to be lower among Japanese couples compared to couples overseas (e.g., [1,21]).

The biodemography project revealed an overall low frequency of intercourse (Table 2.4). Additionally, when the participants were further categorized by their pregnancy intention, only 24% of married women who wanted to become pregnant and were not pregnant at the time of the survey were having intercourse 1+ day per week [1]. The proportion of women having intercourse 1+ day per week was even smaller for those who wanted to become pregnant in the future (14%) or who did not want to become pregnant (12%) [1]. The National Survey of Work and Family in Japan conducted in 2007 [21] also reported low coital frequency (Table 2.5); only 23% of women desiring a child had sexual intercourse at least once a week. The same survey showed that 21% of women aged between 20 and 29 years and 37% of women aged between 30 and 39 years were in sexless marriages, which refers to married or cohabitating couples who have not had any sexual intercourse for more than 1 month (Table 2.5, sum of “once in 2 months”, “once in 6 months”, and “not at all”) [21]. In a series of studies conducted by Arakawa and colleagues [16] to examine a possible association between chemical exposure and TTP, more than 70% of the respondents answered that the frequency of intercourse before their latest pregnancy was equal to or less than once a week (Table 2.6). These data suggest that the frequency of intercourse tends to be low among couples in Japan today, even when the sample is limited to couples who eventually achieved pregnancy or were actively trying to conceive.

[...] Although recent studies report relatively low frequency of sexual intercourse among Japanese couples compared to those in Western countries, studies conducted in the past report a higher frequency of intercourse among Japanese couples. For example, in 1955, Tsukamoto [25] reported that more than 80% of married women had sexual intercourse once a week or more (Table 2.7). Infrequent sexual intercourse among Japanese couples in recent years may be the result of sociocultural factors, including prevalent premarital sex [26], higher unemployment rates, and long working hours among those who are employed [27]. It is also possible that a lower frequency of marital sexual intercourse is often accompanied by active sexual activity outside the marital relationship, although we do not have sufficient data to support or reject this supposition.