Sauna During Pregnancy: What the Research Actually Says

If you search "sauna during pregnancy," most results will tell you the same thing: avoid it. End of story.

But that is not the whole story. Not even close.

In Finland, where sauna is part of daily life, many women continue to use the sauna throughout pregnancy with modifications. Finland has one of the lowest rates of neural tube defects in the world. If sauna were a major risk factor, you would expect the opposite.

The medical concern is real and worth understanding. But the research is more nuanced than a blanket "no." And your healthcare provider, who knows your specific situation, is the right person to help you make this decision.

This guide lays out the evidence, the risks, the precautions, and the practical guidelines so you can have an informed conversation with your provider.

MEDICAL DISCLAIMER: This guide is for educational purposes only. It is not medical advice. Pregnancy is individual. Your OB-GYN or midwife knows your health history, your risk factors, and your pregnancy. Talk to them before making any decisions about sauna use during pregnancy. Do not rely on this or any internet guide as a substitute for that conversation.

TL;DR: The Short Version

The concern is about sustained core body temperature above 101°F / 38.3°C, especially in the first trimester
Some studies link prolonged hyperthermia to neural tube defects, but the evidence is mixed
Finnish women commonly use saunas during pregnancy with shorter sessions and lower temperatures
A 2019 systematic review found no significant increase in adverse outcomes with moderate sauna use
If you choose to sauna while pregnant: lower temperature, shorter sessions, lower bench, never alone
First trimester requires the most caution. Third trimester has different concerns (overheating, swelling, dizziness).
High-risk pregnancies, preeclampsia, and pregnancy complications are absolute contraindications
Talk to your provider. This is not a decision to make from a blog post.

Why the Concern Exists

The worry about sauna during pregnancy comes down to one thing: core body temperature.

When your core temperature rises above 101°F / 38.3°C and stays there, it enters a range called hyperthermia. During the first trimester, when the neural tube is forming (roughly weeks 3-8), sustained hyperthermia has been associated with an increased risk of neural tube defects like spina bifida.

This association comes primarily from studies on prolonged fever during early pregnancy, not from sauna use specifically. High fevers that last hours are different from a 10-minute sauna session. But the underlying mechanism is the same: elevated core temperature during a critical window of development.

This is why most Western medical guidelines err on the side of caution. The American College of Obstetricians and Gynecologists (ACOG) recommends avoiding activities that could raise core temperature above 102.2°F / 39°C during pregnancy.

The question is: does a typical sauna session actually raise core temperature that high?

What the Research Actually Shows

The Finnish Data

Finland has the highest per-capita sauna use in the world. Roughly 99% of Finns sauna regularly, including many pregnant women. Despite this, Finland consistently has one of the lowest rates of neural tube defects globally.

This is not proof that sauna is safe during pregnancy. Other factors are at play, including high rates of folic acid supplementation, excellent prenatal care, and genetic factors. But it is a meaningful data point.

Finnish medical guidelines do not advise against sauna use during pregnancy. They recommend moderation: shorter sessions, lower temperatures, and listening to your body. Finnish obstetricians generally view moderate sauna use as acceptable for uncomplicated pregnancies.

The 2019 Systematic Review

A systematic review published in the British Journal of Sports Medicine (Ravanelli et al., 2019) examined the evidence on heat stress during pregnancy. The review looked at exercise in the heat, hot baths, and sauna use.

Key findings:

Pregnant women did not show core temperature increases to dangerous levels during moderate heat exposure
The thermoregulatory responses of pregnant women appear to be protective. Pregnant women tend to sweat earlier and more efficiently, likely as an evolutionary adaptation.
No significant increase in adverse pregnancy outcomes was associated with moderate sauna use

The authors concluded that the blanket recommendation to avoid all heat exposure during pregnancy may not be supported by the available evidence.

Core Temperature Studies

A few studies have directly measured core temperature during sauna use in pregnant women:

A Finnish study found that 20 minutes in a traditional sauna (at roughly 158°F / 70°C) raised core temperature by about 0.7°C (1.3°F) in pregnant women. For most women, this kept core temperature well below the 39°C / 102.2°F threshold.
Individual variation matters. Some women's core temperature rose more than others. Body composition, hydration status, and fitness level all play a role.

The takeaway: a moderate sauna session probably does not raise core temperature to dangerous levels for most women. But "probably" and "most" are doing a lot of work in that sentence. This is why individual medical advice matters.

Trimester-by-Trimester Guidance

First Trimester (Weeks 1-12)

This is the highest-caution period. Neural tube formation happens in weeks 3-8, and this is the window where elevated core temperature carries the most theoretical risk.

If you and your provider decide to continue sauna use:

Keep temperature low, no higher than 150°F / 65°C
Stay on the lowest bench
Limit sessions to 10 minutes maximum
Exit immediately if you feel any discomfort, dizziness, or nausea
Stay well hydrated

If you are uncertain: Skip the sauna during the first trimester. The risk window is finite. You can revisit the decision in the second trimester.

Many women who are regular sauna users choose to pause during the first trimester and resume later. This is a reasonable and cautious approach.

Second Trimester (Weeks 13-27)

The neural tube has closed. The risk profile changes. Many providers are more comfortable with moderate sauna use during this period.

If your provider approves:

Temperature up to 150°F / 65°C
Sessions of 10-15 minutes
Lower bench only
Water before, during, and after
Exit if you feel lightheaded, overheated, or unwell
Never sauna alone

The second trimester is often when women feel their best during pregnancy. Energy returns, nausea usually fades, and the belly is not yet large enough to cause significant discomfort. If you are going to sauna during pregnancy, this is typically the most comfortable window.

Third Trimester (Weeks 28-40)

New considerations emerge. Your blood volume has increased by about 50%. Your cardiovascular system is working harder. Swelling is common. Balance changes as your center of gravity shifts.

If your provider approves:

Keep it gentle. Temperature at or below 150°F / 65°C.
Short sessions, 10 minutes or less
Lower bench, with room to sit comfortably
Stand up very slowly. Blood pooling and dizziness are more likely now.
Have someone with you
Stop immediately if you notice contractions, dizziness, or any unusual symptoms

Some women find the warmth genuinely helpful for third-trimester aches, particularly lower back pain and joint stiffness. Others find the heat too much. Follow your body's signals.

If You Choose to Sauna During Pregnancy

These rules apply regardless of trimester:

Lower temperature. Stay at or below 150°F / 65°C. This is not the time for a hot session.
Shorter sessions. Ten minutes maximum. You can always do a second short round after cooling down.
Lowest bench only. Temperature is significantly cooler at bench level compared to the ceiling.
Exit immediately if uncomfortable. Any dizziness, nausea, rapid heartbeat, or feeling of overheating means you are done.
Stay hydrated. Drink water before you enter. Bring water in with you. Drink after you exit.
Never alone. Always have someone with you or nearby who knows you are in the sauna.
Cool down gently. Lukewarm shower, not cold plunge. Avoid dramatic temperature swings.
Skip the steam. Heavy steam (throwing water on stones) increases humidity and makes the heat feel more intense. Keep it dry or minimal.

When to Absolutely Avoid Sauna During Pregnancy

Regardless of trimester, do not use the sauna if you have:

Preeclampsia or signs of preeclampsia (high blood pressure, protein in urine, swelling)
Placenta previa or other placental complications
A history of preterm labor or current risk of preterm delivery
Cervical insufficiency
Gestational diabetes that is not well controlled
Any pregnancy complication your provider has flagged
Fever or illness. Your body is already overheated.
Dehydration. Sauna will make it worse.

If your pregnancy has been classified as high-risk for any reason, sauna is off the table unless your provider specifically says otherwise.

For a broader look at conditions that rule out sauna use, see our guide on when not to sauna.

Hot Tubs, Hot Baths, and Saunas: Are They the Same Risk?

Not exactly. Hot tubs may actually pose more risk than saunas during pregnancy. Here is why:

In a sauna, your body can cool itself through sweating. The sweat evaporates and carries heat away. In a hot tub, you are submerged in water. Sweating does not help because the sweat cannot evaporate. Your core temperature rises more quickly and stays elevated longer.

Studies have found that hot tub use is more consistently associated with core temperature increases above the safety threshold compared to sauna use.

If you are choosing between the two, sauna (with precautions) is likely the lower-risk option. But the same principle applies: talk to your provider, keep it moderate, and listen to your body.

Frequently Asked Questions

Can I use a sauna in early pregnancy?

The first trimester is the highest-risk window because of neural tube development. Most Western guidelines recommend caution or avoidance during this period. Finnish women often continue with modifications. If you want to be conservative, skip the first trimester and discuss resuming with your provider after week 12.

Is infrared sauna safer than traditional sauna during pregnancy?

Infrared saunas operate at lower air temperatures (120-150°F / 49-65°C), which may feel more comfortable. However, infrared heat warms your body directly, and the effect on core temperature is not necessarily lower. The same precautions apply: short sessions, moderate settings, and medical clearance.

Can sauna cause miscarriage?

There is no strong evidence linking moderate sauna use to miscarriage. The concern is specifically about sustained core temperature elevation and neural tube defects in the first trimester, not miscarriage. However, if you have a history of miscarriage or a high-risk pregnancy, your provider may recommend avoiding sauna as a general precaution.

What if I used a sauna before I knew I was pregnant?

Do not panic. A single sauna session is unlikely to have caused harm. The concern is about sustained, repeated hyperthermia during a specific developmental window. Mention it to your provider at your next visit, but this is not an emergency.

Can sauna help with pregnancy aches and pains?

Many women find that gentle heat helps with back pain, joint stiffness, and muscle tension during pregnancy. If your provider approves sauna use, a short, moderate session can provide real relief. Just follow the guidelines above.

Sources

Ravanelli, N., et al. "Heat Stress and Fetal Risk: Environmental Limits for Exercise and Passive Heat Stress During Pregnancy." British Journal of Sports Medicine, vol. 53, no. 13, 2019, pp. 799-805. Systematic review finding no significant adverse outcomes with moderate heat exposure during pregnancy.
American College of Obstetricians and Gynecologists (ACOG), Committee Opinion No. 804, "Physical Activity and Exercise During Pregnancy and the Postpartum Period," 2020. ACOG guidelines recommending core temperature stay below 102.2°F / 39°C during pregnancy.
Moretti, M.E., et al. "Maternal Hyperthermia and the Risk for Neural Tube Defects in Offspring." Epidemiology, vol. 16, no. 2, 2005, pp. 216-219. Meta-analysis examining the association between maternal fever/hyperthermia and neural tube defect risk.
Finnish Institute for Health and Welfare (THL), "Sauna and Pregnancy." Finnish public health guidance on continuing sauna use during uncomplicated pregnancies with modified duration and temperature.
Vaha-Eskeli, K., and Erkkola, R. "The Sauna and Pregnancy." Annales Chirurgiae et Gynaecologiae, vol. 77, no. 5-6, 1988, pp. 203-214. Finnish study measuring core temperature responses in pregnant women during sauna use.

The Bottom Line

The question "Is sauna safe during pregnancy?" does not have a universal yes or no answer. It depends on your health, your pregnancy, your trimester, and your provider's assessment.

What we can say:

The research is more reassuring than most internet sources suggest
Finnish women have been doing this safely for generations
Moderate use with precautions appears to be low-risk for uncomplicated pregnancies
The first trimester deserves the most caution
Your provider's opinion matters more than any article, including this one

Print this guide. Bring it to your next appointment. Have the conversation. Your provider knows your body and your pregnancy better than any website ever will.

For general sauna safety fundamentals, start with our sauna safety guide. If you are new to sauna entirely, our beginner's guide covers the basics.

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