Women certainly take hot baths while they are pregnant but the hot tub immerses the body and of course the tendency is to stay in it longer.

When I counsel women about hot tubs, I say that we just don't know, but it makes sense to me to take breaks every 10 minutes and not to have the water over 115 degrees or so.

Just to be absolutely safe, I would recommend just a quick dip. Sitting on the edge is not really recommended either. Although this seems like a low risk, it is possible to pick up bacteria such as pseudomonas that are deposited on the edges of such tubs.There have been reports of hyperthermia causing neural tube defects in offspring and yet this can not be substantiated in all populations. And five months is beyond the time of concern for this particular anomaly. Consider the Finnish who take saunas every week throughout gestation.

The bottom line is no immersion, not too hot and shorter time intervals.