Hot tub alternatives during pregnancy

How do the options compare?

Each heat source is compared on the temperature it actually holds and how long it takes to push core body temperature to the level researchers watch, with the week-6 line running underneath all of it.

• Hot tub and sauna use during pregnancy should be limited, and several studies have reported a small chance of neural tube defects in babies of people who had fever or hyperthermia before the sixth week of pregnancy. 1
• High body temperatures occurring after the sixth week of pregnancy are not expected to increase the chance of neural tube defects, which is why the strictest caution applies to the earliest weeks. 1
• In a study of pregnant women, nobody in a 39.0 degree Celsius tub reached the core temperature of concern before 15 minutes, while in a 41.1 degree Celsius tub it took about 10 minutes, so water temperature changes the timeline sharply. 2
• Maternal hyperthermia has been associated with roughly a two-fold increase in the risk of neural tube defects, with a reported odds ratio of 1.93 and a 95% confidence interval of 1.53 to 2.42. 3
• Hot yoga is practiced in rooms held at 35 to 40 degrees Celsius, and the authors of one review concluded it should be avoided in pregnancy for the same heat reasons that apply to hot tubs. 3

Which option makes sense?

Water temperature is the whole variable: a cooler tub buys about 15 minutes and a hotter one about 10, hot yoga rooms run hotter still, and the concern is weighted toward the first six weeks.

Disclosure: Pregnancy Smart is a supplement maker. The options compared above sit outside our own product line; this page describes their pregnancy evidence on its own merits.