The Japanese have a long tradition of going to hot springs (onsen)—even pregnant women frequently soak. And while in many other countries even a steamy bath is considered risky while pregnant, a 2006 study showed no correlation between the way pregnant women bathed (hot springs, tub baths or showers) and the apgar score of their baby. In other words, there was no evidence that soaking in hot water while pregnant is harmful to ones baby.
Journal of the Japanese Society of Balneology, Climatology and Physical Medicine
VOL.69;NO.4;PAGE.245-250(2006)