Quick answer: Most major medical guidelines, including those from ACOG (American College of Obstetricians and Gynecologists), recommend avoiding sauna use during pregnancy — particularly in the first trimester. The primary concern is hyperthermia (elevated core body temperature), which has been linked to neural tube defects and other fetal development complications in animal studies and some human epidemiological data. When in doubt, consult your OB or midwife before any sauna use during pregnancy.
Note: This article provides general health information only. It is not medical advice. Always consult your healthcare provider before making decisions about sauna use during pregnancy.
The Core Concern: Hyperthermia
The primary risk of sauna use during pregnancy is hyperthermia — an elevation in core body temperature above 38.9°C (102°F). A typical sauna session at 80–100°C raises core body temperature by 1–2°C, which can push a pregnant woman into the hyperthermia range depending on her baseline temperature, session length, and individual physiology.
Hyperthermia during the first trimester is associated with an increased risk of neural tube defects (conditions affecting the brain and spinal cord) in multiple animal studies and some human epidemiological research. The embryo is most vulnerable during the first 4–6 weeks of development — often before a pregnancy is confirmed.
According to ACOG guidelines, pregnant women should avoid activities that raise core body temperature above 38.9°C for extended periods, which includes sauna use, hot tub soaks, and similar high-heat exposures.
What the Research Shows by Trimester
First Trimester (Weeks 1–12): Highest Risk
This is the period of greatest concern. Neural tube closure occurs between weeks 3–4 of pregnancy. Major organ systems are forming throughout the first trimester. Heat exposure during this window carries the most significant developmental risk. Most guidelines recommend avoiding sauna entirely during the first trimester.
Second Trimester (Weeks 13–26): Lower Risk, Still Caution Warranted
Major organ development is largely complete by the second trimester, reducing the hyperthermia risk to fetal development. However, elevated core temperature still increases maternal heart rate and can reduce placental blood flow. The physiological demands of pregnancy — increased blood volume, elevated resting heart rate, thermoregulatory changes — mean that the cardiovascular stress of sauna is greater during pregnancy than outside it. Short, lower-temperature sessions with careful monitoring may be acceptable for some women with medical clearance.
Third Trimester (Weeks 27–40): Individual Assessment
By the third trimester, the developmental risk from hyperthermia is lower, but the cardiovascular demand of sauna use is highest — maternal blood volume has increased by 40–50%, the heart is working harder, and the body's thermoregulatory capacity is reduced. Many women find the heat simply uncomfortable or exhausting at this stage. Medical guidance varies; individual consultation with an OB or midwife is essential.
Factors That Increase Risk
- Session length: Longer sessions produce greater core temperature elevation. Even at lower temperatures, staying in longer increases risk.
- Dehydration: Pregnancy increases baseline fluid needs. Starting a sauna session dehydrated raises risk significantly. According to fluid loss research, a sauna session produces 300–600ml of sweat loss — on top of already-elevated pregnancy fluid demands.
- Upper bench position: Higher bench = higher temperature = higher core temperature rise.
- Pre-existing conditions: High blood pressure, gestational diabetes, preeclampsia, or any condition affecting cardiovascular function significantly increases risk.
- Multiple pregnancies (twins, etc.): Higher baseline physiological demand.
Safer Alternatives During Pregnancy
If you have used sauna regularly and miss the relaxation and stress relief benefits during pregnancy, these alternatives provide some of the same effects with significantly lower risk:
- Warm (not hot) bath: Water at 37–38°C provides relaxation without core temperature elevation risk. Exit if you feel too warm.
- Infrared sauna at low temperature (50–55°C): Lower heat than traditional sauna; some practitioners consider low-temperature infrared sessions with short duration acceptable during second and third trimester with medical clearance. Consult your provider.
- Steam room at low duration: 5–10 minutes maximum; lower temperature than traditional sauna. Still requires medical guidance.
- Prenatal massage: Produces relaxation and parasympathetic activation without thermal risk.
- Moderate exercise: Swimming and walking produce many of the same cardiovascular and mood benefits as sauna during pregnancy, and are generally considered safe with appropriate modifications.
If You Used Sauna Before Knowing You Were Pregnant
This is a common concern. If you used a sauna early in pregnancy before knowing you were pregnant, the actual risk depends on the timing, temperature, and duration of exposure. A single short session early in pregnancy does not guarantee harm — the risk is probabilistic and depends on multiple factors. Discuss the specific circumstances with your OB or midwife. Most healthcare providers will offer reassurance and, if indicated, additional monitoring.
Hydration During Pregnancy Near Sauna Environments
Even if you choose not to use the sauna during pregnancy, if you are attending a sauna event like the Mammoth Mug Sauna Rave at NRG Toronto while pregnant, the warm ambient environment and social activity still increase fluid demands. Pregnant women need significantly more fluid than baseline — approximately 2.3–3L per day according to ACOG nutrition guidelines — and should increase this further in warm environments.
The Mammoth Mug 2.5L covers the full-day hydration target for a pregnant woman in one fill, making it easy to track intake and stay on top of the elevated fluid needs that pregnancy requires. For the full hydration science, see our guide on post-session rehydration and our deep-dive on sauna dehydration.
Related Articles
- 7 Sauna Health Benefits Backed by Science
- Beginner Guide to Sauna: Everything You Need for Your First Session
- Sauna Dehydration: How Much Fluid You Lose
- How Much Water to Drink After a Sauna
- Sauna Rave Toronto: NRG Event Guide
Frequently Asked Questions
Can I use a sauna in the second trimester?
The risk is lower in the second trimester than the first, as major organ development is largely complete. However, cardiovascular stress from sauna is still elevated during pregnancy, and individual risk varies significantly based on health status, pregnancy complications, and baseline fitness. The most important step is to consult your OB or midwife before resuming sauna use at any point during pregnancy — many will provide individualised guidance based on your specific situation rather than a blanket recommendation.
What temperature is safe for sauna during pregnancy?
There is no established "safe" temperature threshold for sauna during pregnancy — the concern is core body temperature elevation above 38.9°C (102°F), which can occur at various ambient temperatures depending on duration and individual physiology. Lower temperatures (60–70°C) for shorter durations (5–10 minutes) reduce but do not eliminate the hyperthermia risk. Any sauna use during pregnancy should be discussed with your healthcare provider before proceeding.
Is infrared sauna safer than traditional sauna during pregnancy?
Infrared saunas operate at lower ambient temperatures (50–65°C vs 80–100°C for traditional saunas), which may reduce the rate of core temperature increase. However, the core concern — hyperthermia — can still occur with infrared sauna, particularly with longer sessions. The lower temperature makes short sessions more manageable, but does not make infrared sauna automatically safe during pregnancy. Consult your healthcare provider regardless of sauna type.
Can I be near a sauna (in the changing room or cool-down area) while pregnant?
Being in a warm environment adjacent to a sauna — changing rooms, cool-down areas, warm pools — does not carry the same risk as sauna use itself. The ambient temperature of these areas is typically 25–30°C, which does not produce the core temperature elevation associated with developmental risk. Stay hydrated, avoid overheating, and exit immediately if you feel uncomfortable. The main risk is dehydration in a warm environment — keep your water intake high throughout.
When can I return to sauna use after giving birth?
Most guidelines suggest waiting until your postpartum check-up (typically 6 weeks after vaginal birth, longer after caesarean section) before resuming sauna use. Your body's thermoregulatory and cardiovascular systems need time to return to pre-pregnancy baseline. Once cleared by your healthcare provider, you can resume normal sauna use — the cardiovascular and recovery benefits are particularly valuable during the postpartum period when sleep is disrupted and physical recovery is ongoing. See our sauna health benefits guide for the full evidence base.
What does the research say about sauna and birth defects?
The primary concern is neural tube defects (NTDs) in the first trimester. A meta-analysis in the American Journal of Obstetrics and Gynecology found that maternal hyperthermia (core temperature above 39°C) during weeks 3–8 of pregnancy was associated with a 2x increased risk of NTDs, including spina bifida. This is why most medical guidelines advise avoiding sauna during the first trimester specifically. Notably, Finnish studies where women continued moderate sauna use (shorter sessions, lower temperatures) throughout pregnancy did not show elevated NTD rates — suggesting duration and temperature control matter significantly.
Can my partner use the sauna while we are trying to conceive?
For male partners: regular sauna use temporarily reduces sperm count and motility. A Finnish study found that bi-weekly sauna use reduced sperm concentration by 25–30% — the effect was fully reversible within 3–6 months of stopping. If actively trying to conceive, male partners should reduce sauna frequency to once per week maximum or take a 3-month break from sauna to allow full spermatogenesis recovery. For female partners: there is no evidence that sauna affects ovulation or fertility, but most practitioners advise caution during the two-week wait between ovulation and expected menstruation.
What alternatives to sauna exist for pregnant women who want relaxation benefits?
Warm baths (not hot — keep water temperature below 38°C), prenatal massage, prenatal yoga, and meditation provide overlapping relaxation benefits without the core temperature risk. A warm bath at 37°C raises core temperature by only 0.3–0.5°C, well within the safe range. Some women find the cool-down area of the sauna facility — sitting near the sauna without entering, enjoying the social environment — satisfies the ritual and social component of their sauna practice. Always discuss any heat exposure plan with your obstetrician or midwife.