One Hot Mama! Hot Tubs In Pregnancy

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.