Directions for Future Research

  • Shoko Konishi
  • Emi Tamaki
  • Jun Yoshinaga
Part of the SpringerBriefs in Population Studies book series (BRIEFSPOPULAT)


In the earlier chapters of this book, we have shown, with limited evidence, that both the duration of lactational infecundability and time to pregnancy (TTP) may be longer among Japanese couples than among Western couples. Longer TTP can be linked to the relatively low coital frequency and prolonged duration of lactation found in couples and mothers in Japan, as well as to other factors such as long work hours, underweight, and overweight. The relatively longer TTP may be linked to the frequent use of ART among couples in Japan. Efficient use of ART, in terms of who should utilize these technologies and at what time, should be investigated in future studies to better meet couples’ needs. We confirm the widely held notions that many Japanese couples continue to rely on unreliable contraception and that induced abortion is common among both married and unmarried women. Conceptions that end in artificial abortions could have a significant impact on fertility trends in Japan if social and other circumstances allowed some of those conceptions to result in live births. It is also important to investigate the biological and sociocultural factors—e.g., exposure to chemical substances, body size, educational level, and working conditions—that may explain variations in TTP and other proximate determinants of fertility. In addition, a model-based approach would enable us to estimate the level of change in each sociocultural factor that would lead to changes in fertility through the modification of proximate determinants. We believe that the accumulation of such data will help us to understand why low levels of fertility persist in Japan.


Underweight Overweight Chemical exposure Infertility treatment Lactational amenorrhea Time to pregnancy (TTP) Japan 


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Copyright information

© The Author(s) 2018

Authors and Affiliations

  • Shoko Konishi
    • 1
    • 4
  • Emi Tamaki
    • 2
  • Jun Yoshinaga
    • 3
  1. 1.Department of Human Ecology, School of International Health, Graduate School of MedicineThe University of TokyoTokyoJapan
  2. 2.Faculty of International Social SciencesGakushuin UniversityTokyoJapan
  3. 3.Faculty of Life SciencesToyo UniversityGunmaJapan
  4. 4.Department of AnthropologyUniversity of WashingtonSeattleUSA

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