One Hot Mama! Hot Tubs In Pregnancy

by Dr. Michele Brown OB/GYN

pregnant woman lounging in hot tubThe warm fragrant waters of elegant spas around the world are often filled with fully submerged, happy, pregnant women. Why? Because pregnant women can be plagued with multiple body aches and discomforts caused by rapid expansion of the abdomen. This is especially true in the third trimester when we OBs hear many complaints of pelvic discomfort and severe lower back pain.

Our recommendations vary from massage, maternity supports, chiropractor visits, and the like but a warm bath, shower, jacuzzi or hot tub is often the most accessible modality for relief a patient's aching joints and muscles. A woman can go home and kick back with a good book in her own bathtub, or get her husband to spring for a weekend at a luxurious spa. Ahhhhh, what a relief!

Is Heat Safe for the Developing Fetus?

Is this yet another simple pleasure which may not be safe for our unborn babies? Allow me to share the latest research so you and your doctor can make the right choices.

Intense heat has been found to cause fetal malformations in many animal species like chickens, mice, guinea pigs, monkeys and pigs. Past older literature also attributes high maternal temperatures with multiple congenital anomalies in humans, especially when exposure occurs in the first trimester. Risks of neural tube defects is estimated to be about two to four times higher when a first trimester mom's body overheats, either from an external source, such as a hot tub or sauna, or from an internal source such as a fever.

Among the anomalies described are:

  • Neural tube defects
  • Anencephaly
  • Microcephaly
  • Retardation
  • Seizures
  • Decreased muscle tone
  • Hirschprung's disease (congenital Intestinal blockage)
  • Omphalocoele (abdominal wall defect)
  • Limb defects
  • Hypospadias (urethral is not located at tip of penis)
  • Cardiac defects
  • Miscarriage
  • Facial anomalies such as micrognathia (small jaw), external ear anomalies, microphthalmia, (small eye development) and midface hypoplasia (underdevelopment of the middle of the face)

Some recent studies (2003 by Hertz-Picciotto) are skeptical about attributing hot tub use with miscarriage. Poorly designed studies with low numbers of participating subjects, lack of stratification of data based on age of the pregnant women that participated in the studies, (older mothers have more of a tendency towards miscarriage anyway) along with some inconsistencies in the findings, prevent definite links between hot tub use and miscarriage.

What Causes These Anomalies?

Facial features and the neural tube regions form occur from week 4 to week 16 in utero. This is the critical time in development where these organ systems can be affected by elevated maternal temperatures.

Crucial Periods of Development
Pregnancy Stage Organ System
Week 4 Development of the head and neck region, this includes regions of the spinal cord, brainstem, forebrain, midbrain, hindbrain, ventricles, and ganglion
Week 5 -Face development including formation of the forehead, mandible, and maxilla;
-Beginning development of the eye, ear, and nose
-Beginning development of the spinal nerves and cranial nerves
-Heart becomes 4 chambered organ
-External genitalia begins to form
Third Month Gut develops outside the body and then returns inside
Fourth Month Chin appears

Are Studies Accurate and Reproducible?

Studies are inconsistent in their findings. Many are anecdotal with few subjects. Others are retrospective and after an anomaly is found, associations of possible causative factors are sought to explain the anomaly.

One study in 1979 (Uhari, British Med Journal) examined the effects of saunas on pregnant Finnish women and found no association with congenital defects in infants. This may be attributed to the lower temperatures used by Finnish women and shorter times spent (6 to 12 minutes) in the sauna compared to American women.

Another study published in JAMA in 1992 by Milunsky was a prospective study that followed 23,491 women in the New England area. Women with exposure to hot tub, sauna, or fever early in pregnancy were found to be 2.2 times more likely to have a fetus with a neural tube defect compared to women without this exposure. Hot tub exposure appeared to have the strongest effect compared to all the other ways elevated temperature can occur.

Is Hot Tub Use More Risky than Saunas or Maternal Fever?

It is thought that immersion in hot water will raise the body temperature to a higher level for a longer period of time compared to a sauna or maternal fever where perspiration and body temperature cooling through evaporation are more likely to occur. The exact reason why heat itself can cause anomalies is unknown but possible mechanisms include theories of cell damage, cell death, disruption of mitosis, and prevention of cell migration. Heat may also cause placental necrosis and death, and vascular lesions.

How Hot is Too Hot?

Prolonged elevation of a woman's body temperature to 38.9° degrees C (102° F) was determined to be the critical level that can cause anomalies. The critical time frame for a woman's body to reach this temperature was 15 minutes in a 39° C (102.2° F) tub or 10 minutes in a 41.1 ° C (106° F) tub.

It was found that prolonged high temperatures or multiple temperature spikes at lower temperature elevations had worse effects than a single temperature spike.

What about Electric Blankets?

A JAMA study (Milunsky, 1992) found that exposure to an electric blanket was not associated with increased risk of neural tube defects.


Although there is some controversy regarding some of the studies, exposure of pregnant women to heat in the first trimester via a hot tub, sauna, or fever is associated with an increased risk of neural tube defects.

I highly recommended that obstetricians, health clubs, private stores selling equipment, and other facilities with hot tubs and saunas warn pregnant women of these risks their baby when pregnant women are exposed to elevated temperatures for prolonged periods of time.

In addition, the range of temperature in the saunas and hot tubs should be posted along with warnings of recommended exposure times. To be safe, pregnant women should be exposed to temperatures less than 100° F for under 15 minutes only after the first trimester. To play it even safer, many mothers should avoid hot tubs and saunas altogether until after they have delivered.

Dr. Brown, founder of Beauté de Maman, is a board-certified member of the American College of Obstetrics and Gynecology, a member of the American Medical Association, the Fairfield County Medical Association, Yale Obstetrical and Gynecological Society and the Women's Medical Association of Fairfield County. She is a magna cum laude graduate of Tufts University, completed her medical training at George Washington University Medical Center and completed her internship and residency in obstetrics and gynecology at Yale-New Haven Hospital. Dr. Brown has a busy obstetrical practice in Stamford, Connecticut and, as a clinical attending, actively teaches residents from Stamford Hospital and medical students from Columbia Presbyterian Hospital in New York.

Copyright © Michele Brown. Permission to republish granted to