Saunas/hot tubs

What are they?

Saunas are small chambers that generate wet and dry heat, typically between 70°C and 100°C. Hot tubs are spa baths that contain water at temperatures of up to 40°C. Both are generally used for the purpose of relaxation and to enhance well-being.

Is it safe to use saunas and hot tubs in pregnancy?

There is no yes or no answer to this question. The studies that have investigated whether use of saunas or hot tubs in pregnancy might increase the risk of adverse pregnancy outcomes have produced mixed findings. It is therefore not possible to confirm that their use is safe. For this reason, some women prefer not to use saunas or hot tubs if they suspect or know that they are pregnant.

What if I have already used a sauna or hot tub during pregnancy?

Some women might wish to avoid further use of saunas or hot tubs as a precautionary measure. If you are worried because you have already used a sauna during pregnancy it is worth bearing in mind that in countries such as Finland, where most women use saunas throughout pregnancy, rates of adverse pregnancy outcomes are similar to those in countries where saunas are not routinely used.

Can using a sauna or hot tub in pregnancy cause miscarriage?

No studies have investigated whether sauna use in early pregnancy affects a woman’s chance of having a miscarriage.

A single study of around 1,000 pregnant women showed that those who used a hot tub in early pregnancy were about twice as likely to have a miscarriage compared to women who had not used a hot tub. The risk of miscarriage appeared to be highest in women who used hot tubs frequently and at higher temperatures. More research is required to confirm this finding.

Can using a sauna or hot tub in pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that birth defects can occur.

Neural tube defects
There are theoretical concerns (based largely on the results of animal experiments) that an increase in the mother’s body temperature to around 40°C during use of a sauna or hot tub might increase the risk of neural tube defects such as spina bifida in the baby.

None of the three studies that investigated use of saunas in early pregnancy provided any evidence of a link with an increased risk of neural tube defects in the baby. Additionally, in Finland, where most women use saunas throughout pregnancy, the occurrence of neural tube defects is similar to that in most other European countries.

The four studies that have investigated whether hot tub use in early pregnancy might increase the risk of neural tube defects in the baby have produced mixed findings. There are, however, possible problems with some of the methods used in these studies. Further research is therefore required before we can say whether use of hot tubs in early pregnancy increases the risk of neural tube defects in the baby.

A study of non-pregnant women showed that those in a sauna set at 81°C could not tolerate the heat for long enough to allow their body temperature to rise to 40°C. In this study, women had to spend at least 15 minutes in a hot tub with a water temperature of 39°C before their body temperature rose to around 40°C. Pregnant women who wish to continue using saunas or hot tubs may therefore choose to limit time periods of exposure and/or reduce the sauna or hot tub temperature to avoid a significant rise in body temperature.

Women trying to conceive and all pregnant women in the first trimester are advised to take 400 micrograms of folic acid daily to reduce the risk of neural tube defects in the baby. For more information please see the bump leaflet on use of folic acid in pregnancy. It is not known if taking folic acid before or during early pregnancy offers any protection against any possible effects of hot tub or sauna use.

Other birth defects
Small numbers of studies have provided no evidence that use of saunas or hot tubs in early pregnancy is linked to specific birth defects including heart defects and cleft lip and palate. A single study provided weak evidence of a possible link between hot tub use in early pregnancy and gastroschisis (where some of the baby’s bowel protrudes outside of the baby’s body through a hole next to the tummy button) and oesophageal atresia (where the tube leading from the baby’s mouth to the stomach has not developed properly and does not connect the two). However, further studies which analyse information on much larger numbers of pregnant women who use saunas and hot tubs are needed before any link can be confirmed or ruled out.

Can using a sauna or hot tub in pregnancy cause stillbirth?

No studies have investigated whether stillbirths occurs more commonly in women who use saunas or hot tubs in pregnancy. However, there is a report in a scientific journal of 23 women who spent 20 minutes in a sauna at 70°C during or after the 36th week of pregnancy. All of the women had healthy babies. Further research is required to determine whether use of saunas and hot tubs in pregnancy affects the risk of stillbirth.

Can using a sauna or hot tub in pregnancy cause preterm birth or my baby to be small at birth (low birth weight)?

No studies have investigated whether preterm or low birth weight babies are more common in women who use saunas or hot tubs in pregnancy. Research into these subjects is therefore required. There is, however, a report in the scientific literature of 23 women who were all at least 36 weeks pregnant when exposed to 20 minutes in a sauna at 70°C. None of the babies were preterm.

Can using a sauna or hot tub in pregnancy cause learning and behavioural problems in the child?

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

There are currently no scientific studies that have examined learning and behaviour in children of women who used saunas or hot tubs during pregnancy.

Will my baby need extra monitoring during pregnancy or after delivery?

As part of their routine antenatal care most women will be offered a scan and blood tests from around 11 weeks of pregnancy and a further scan at 20 weeks of pregnancy to screen for birth defects in the baby. Use of a sauna or hot tub in pregnancy is not expected to cause problems that would require extra monitoring of your baby.

Are there any risks to my baby if the father has used a sauna or hot tub?

No studies have specifically investigated whether use of a sauna or hot tub by the father can harm the baby through effects on the sperm, however this is thought to be unlikely.

Who can I talk to if I have questions?

If you have any questions regarding the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from www.uktis.org.