Photo from Mount Royal, Frisco, Colorado.

"That is happiness; to be disolved into something complete and great. When it comes to one, it comes as naturally as sleep." - Willa Cather

Thursday, 3 February 2011

Daring to discuss teratogens in the culture of blame and guilt

I know I am in over my head. Once again the disclaimer: I'm not an obstetrician. And now I'm adding this one: I'm not an expert on teratogens.

But, that being said, I feel it is my role to bring a little balance back into the universe. I get very angry when I see discussion forums where women discuss what it was that caused their miscarriage, their baby's neural tube defect, etc. There are just endless comments such as this: "I had a fever when I was 3 weeks pregnant and a miscarriage at 6 weeks. People try to tell me that is not what caused it, but I know better...". Come on now. Fevers are common. Miscarriages are common. A woman having a fever and then a miscarriage proves nothing. And bear in mind, women who have a fever and don't develop any problems never write anything. This is how myths develop. The women who write these comments think that they are helping solve the mysteries of the human body. But they are actually doing a huge disservice to other women who become fearful after they develop a fever.

Now for a little personal background: I am a professional sauna sitter.

That is not me in the picture. If it were, I'd be naked like all the other Danes.

Actually, I am not a professional. I just sit in a sauna about 3 times a week. When I got pregnant, I didn't think twice about continuing, granted I can't sit in there nearly as long. I even told my swimming friends about my pregnancy in the sauna. Tons of pregnant women sauna sit in Denmark; it is simply part of the culture here. One day, a woman was telling me a personal story in the sauna and I suddenly got the emergent need to GET OUT. When I got out, I felt terrible in like the primordial terrible kind of way. I almost threw up, but didn't. This was the first time I thought "maybe that wasn't so healthy". But I reassured myself that pregnant women get fevers all the time (with certainly higher core temperatures for longer periods of time) and end up with perfectly healthy babies. If we've evolved through fevers, we must be able to tolerate saunas.

But what does research show?

In 2002 a study was done in Denmark in 24,000 pregnant women demonstrating no relationship between fever and miscarriage or still birth, regardless of how high the fever was or how long it lasted. So one must conclude that if there is an association, it is a very small one because this was an exceptionally large study. (The Lancet, Volume 360, Issue 9345, Pages 1552 - 1556, 16 November 2002 )

What about neural tube defects? Well I will point out first an observational study from Finland where they found that 98.5% of expectant mothers visited the sauna regularly and that Finland has close to if not the lowest percentage of neural tube defects in the world. Now, that is not to say saunas are beneficial, just to say that they are likely not very harmful (Saxén, Sauna and congenital defects, Teratology Volume 25, Issue 3, pages 309–313, June 1982).

So where did all the fear come from? First animal studies. And then a study in the Journal of the American Medical Association in 1992. In a study of nearly 24,000 pregnant women, there was no significant association between any single heat exposure (hot tub, sauna, electric blanket or hot tub) and neural tube defect when they were examined together randomly. BUT there was an association between hot tube use and neural tube defect that was significant. This was NOT true for fevers, electric blankets or saunas. From this, somehow it was deduced that any heat exposure (including that from exercise!) was potentially dangerous to the developing fetus. THIS (and animal studies) is where the "don't overheat during exercise while pregnant" comes from. Read the study for yourself and decide what you think (Mulinsky et al JAMA. 1992 Aug 19;268(7):882-5.). My personal interpretation of this is it tends to be women of a lower socioeconomic class that frequent hot tubs in the US while pregnant and that this group also tends to have poorer nutrition and higher percentages of substance and alcohol abuse. This was not controlled for, likely because they thought the study would not get published if they did not show any significant associations (studies with positive associations are about 9 times more likely to be published).

Bottom line - don't worry about an increase in body temperature from exercise in pregnancy inducing a neural tube defect (neither fevers nor saunas have an association, so why should exercise, which almost always rises the core body temp less?)But watch out for yourself like usual! Heat stroke is always dangerous (but is, by the way, much less likely while pregnant due to improved heat dissipation). I am still uncertain what the significance of the hot tub - neural tube defect is.

But now you can see why I didn't go into Ob-Gyn in the US. Can you imagine the lawsuits?! But on this blog, I feel free to give you all my honest opinion. Heck, when it comes to pregnancy, I am a scardy-cat. But no one needs to worry about things that aren't actually dangerous.

Remember, we are all nomads from Africa genetically - it simply doesn't make sense that an increase in body temperature from exercise would be dangerous.


There has been a little banter going on between Piccola Pinecone and myself about whether or not a female's core body temperature rising slows down sperm transport, thus decreasing fertility. PPC said that she had read this in a Clapp book (does he have more than one?). Anyhow, I have not been able to find this study or any related study for that matter, but I simply want to point out why this theory doesn't make sense to me.

Sperm like to live in relatively cool temperatures. That's why they live outside the body (in the testicles). It is well documented that a rise in temperature in "the balls" causes DNA damage to the sperm and can affect fertility. But certainly once sperm enter the female body (or go into their active state), they have to be "ready" for the increased temperature inside the female body. Otherwise none of us would be here. And if an increase in a woman's body temperature (from for example exercise) negatively impacts the sperm, why is it evolutionarily speaking that we get so warm (as in exercise) during the actual act of baby making?

Okay, that last part was more "something to chew on" :) rather than proof of anything.

Running songs of the day:

Something old - Jesus He Knows Me by Genesis
Something new - Freedom Hangs like Heaven by Iron & Wine


kathleen said...

hm. i always thought neural tube defects were from lack of folate. never heard that heat caused it.

i don't think saunas are bad. i don't think raising your core temperature is bad unless it makes you feel bad. when i was 4 months pregnant my husband and i went to washington dc for the 4th of july. it was 110F degrees in the shade. what did we do one morning? go for a run. granted i couldn't run fast... it was too hot. but i stayed hydrated, ran slower and felt great.

at some point you look at miscarriage and you think to yourself, there are crack babies born everyday. there's no way those 10 minutes in a sauna or 1 cup of coffee caused a miscarriage.

pernillesarup said...

Regarding the hot tub hypothesis: Apart from a range of possible confounding factors, which you already mention, there is always the possibility of a type I error.

Did they test which “activity” raised the core temperature of the women most? The only logical explanation I could think of is if hot tubs raised the temp faster (likely) or to higher levels (I doubt that) making it more stressful for the fetus.

I think that sperm is non resistant to heat during production, but not necessarily afterwards. Otherwise the male plumbing would also be a problem.

Steph said...

Sea Legs Girl,
I love reading your analyses and research about different studies. I hear you on all of that. I guess I keep coming back to these questions that I have to ask myself as the person who is ultimately responsible for the safety of my baby until he is born. When 9 out of 10 OBGYNs (who have seen MANY pregnancies, miscarriages, and defects and stillbirths) and when organizations such as the Organization of Teratology Information Services or The American College of Obstetricians and Gynecologists advise strongly against an activity, why would I go against their advice?

I guess it is not enough for me to second guess the source of their recommendation when much of their careers and (with respect to the above-named organizations) the whole purpose of their existence is dedicated to researching and making these types of recommendations. I suspect that their resources are VASTLY more extensive than mine.

The answer for me, therefore, would be that I would need to be somehow convinced that whatever activity we are talking about (being it excessive exercise (NOT moderate exercise, which is actually recommended), sitting in hot tubs, saunas, or whatever) might have some benefit for the baby. If there is no evidence that it benefits the baby, and all of the above advise strongly against it, why would I still do it? If the answer is “because it makes me feel good, even though I could get by for nine months without it,” is that a responsible decision?

Can’t seem to get past that.

sea legs girl said...


You bring up a question I have - do doctors recommend against sauna use in the US? One sees signs up all over around hot tubs (and I actually never knew why my last pregnancy) but I never actually heard a doctor or midwife recommend against them either.

Then let me challenge your way of thinking. Let us say that you moved to Finland and there your doctor recommended sauna sitting as part of a healthy pregnancy. Would it suddenly be more right than it had been in the US? I am just saying that actually knowing the studies makes me feel safer than simply trusting the authorities.

sea legs girl said...


I'm sitting here wondering what the chance is that you're not a Dane with that first name...

Anyway, great point about the amout of heat exposure. The heat exposure is WAY more in a hot tub and they mentioned that in the study. Well, it's not way more than in a fever, but way more than a sauna or heating blanket. Not sure why I didn't mention it. Great point!

sea legs girl said...


Totally agree :). My first pregnancy weeks with The Lorax were spent doing 2-3 hour runs without shade in the over 100 degree midsummer Oklahoma sun. The thought never once crossed my mind that it might be dangerous to the baby's development. Nor did SR get concerned. He was more concerned about the sketchy homeless men I ran by - for good reason!

pernillesarup said...

Yep, I’m a Dane.
Actually I’d expect (from experience with Drosophila ;-)) that the ramping speed might be as or more important than the final rise in temperature. A slow increase in temperature allows the organism to adjust, start an ample stress response, and suffer a higher temperature without permanent damage. We’re not really adapted to sudden submersion into hot water (which conveys heat to the body much more efficiently that air).

And to supplement your example from Finland I never heard a word against hot tubs, exercise or saunas from anyone (neither from professionals or “ammestue” talk) during my two pregnancies. Actually warm baths was recommended to soothe labor pains, and it worked too! Mind you that was 12 and 14 years ago. Anyways, the neural tube defect manifests itself during the first weeks/months of pregnancy, you should be in the clear on that one :-).

sea legs girl said...


It is funny. I actually wrote that about the rapid rise in temperature from hot tubs maybe being the most dangerous. But then thought - doesn't out temperature also rise really quickly when we have a fever? It sure seems like it anyway.

There is just something so cool in saying "from my experience with Drosophila". :).

Steph said...

Sea Legs Girl,

Yes, physicians and those organizations that I mentioned do recommend against saunas in the US (see below). Do physicians in Finland actually recommend sitting in saunas or hot tubs as part of a healthy pregnancy? If that is the case, then I would want to know why there is a difference of opinion. If they agree with the American physicians and pregnancy organizations, then I would not second guess their resources (for reasons already stated -- i.e., qualifications, expertise, and most importantly, experience with actual pregnancies). These activities that I'm referring to seem to be areas where most, if not all, of the experts agree.

For your question on saunas, see e.g.,: Also, I have very recently seen notices posted by hot tubs and saunas at gyms indicating they are not safe for pregnant women.

Steph said...

Sea Legs Girl,

In response to your question, yes, physicians in the US do recommend against hot tubs and and saunas in the U.S. See link to U.S. Pregnancy Association recommendation below. I've also recently noticed postings near hot tubs and saunas at gyms warning against use by pregnant women.

Do physicans in Finland really recommend sitting in saunas as a part of a healthy pregnancy? If so, then I would be interested in the reasons for the difference, but I don't think that they really do. These areas that I am talking about are not areas where there is a striking debate or division of opinion among the experts. The activites that I'm referring to are the ones in which a most, if not all, of the experts agree. In those cases, for reasons previously stated (i.e., resources, expertise and most importantly experience with actual pregnancies), I'm reluctant to second guess their advice based upon one or two studies that I'm able to dig up. My thinking is that they are in a much better position to see the entire "big picture."

Steph said...

noticed that the link won't paste in completely for some reason. The last of the link above should be /saunas.html

Brianne said...

How do you figure that it is mostly women with lower socioeconomic status that frequent hot tubs?! I've never heard of there being hot tubs in trailer parks or the projects.....I only know of them at swimming pools and gyms - things not terribly frequented by the poor.

sea legs girl said...

Good question Brianne. Simply because there are signs up everywhere around hot tubs not to go in them when pregnant and it tends to be young poor women who don't know they are pregnant right away. And it is only the first 8 weeks gestation that really matter.

Hot tubs are not just for the upper class in the US - they are everywhere (waterparks, cheap hotes, etc.).

Diana said...

You're right about message boards: those places are terrible breeding grounds for modern-day myths. I try to stay away from them, because they usually only ever irritate me.
Thanks for breaking down the study and discussing the effects or non-effects of a higher core temperature on a developing fetus.

I'd like to echo Brianne's comment about the use hot tubs. I'm not sure I would break up usage along socio-economic lines, although I suddenly feel the urge to see if there is a statistic on that.

Do you find that, in general, American medical advice tends to take a more cautious approach when it comes to the activities pregnant women should be doing? Hot tubs and saunas are just part of a long list of "don'ts" pregnant women encounter

Stefanie Schocke said...

This post (and the comments) are exactly why I love your blog. Love that you post scientific research and love the back/forth between all the readers.

Kate said...

My gut instinct is like Brianne's -- I just wouldn't think that hot tubs would be more frequently used by the lower socioeconomic classes.

We are all guessing, but I wonder if there's any data on that. : )

I just think that the truly lower class are not making it to waterparks, cheap hotels, or anywhere else with a hot tub.

Anonymous said...

The neural tube forms at about 17 days gestation, and therefore the problems associated with neural tube defects also occur very early in pregnancy, most often before a woman even realizes that she is pregnant.

A correlation between high fever during pregnancy and mental health issues such as schizophrenia has been found in some health studies. That's why pregnant women are advised not to use saunas and hot tubs.

Exercise does raise core temperature, but only slightly, and our bodies have several fetal protective adaptations, such as increased sweating and respiration and vasodilation which help prevent maternal overheating.

In a sauna or hot tube, our abilities to dissipate excess heat is diminished. For this reason too, "hot yoga" or aerobic exercise in high temperatures and humidity are not recommended during pregnancy.

Grace in TN said...

It is my understanding that electric blankets are not recommended during pregnancy due to the fact that they give off low level electromagnetic fields which may be harmful, not that the heat is harmful.

sea legs girl said...

First- yeah, Stefanie - that is totally what I love about blogging. Thanks to everyone for contributing to discussion.

Now re hot tubs and social class. I need to be clear that I just think is liklier that women who go in hot tubs while pregnant are less educated, perhaps poorer - I mean there are signs everywhere. I'm not trying to be condescening, just thinking what I would have controlled for in this study. Got to wonder if these same women were likely to ignore other recommendations.

Be Fit Mom

Thanks for commenting. I did run across the studies about schizophrenia but found them very inconclusive and frustrating to read. It reminded me of the whole vaccination-autism connection. But do you know of a well-designed study which has shown a significant association?
Re neural tube devlopment, my impression from Embryology was that it occurs over weeks (wasn't it gesation weeks 3-8 approximatel?) and not just on one day.

Grace - gotta admit my ignorance about electic blankets and electromagnetic fields. Sounds like there is yet another potential teratogen I could read about :). I find electic blankets dangerous just because of the fire hazard!

Fast Bastard said...

As a guy who isn't as emotionally involved in this, I have to say a few things.

The anonymous poster who talked about schizephrenia may have been joking but I don't think she was. Let's be clear that the reason pregnant women ar advised not to sit in hottubs has nothing to do with schizophrenia. Again, it sounds funny, but I don't think the poster was aiming for this.

Women who are pregnant tend to be a little anemic. More importantly, they have fluid shifts, including swollen legs. Sitting in a hot tub, and to some degree in a sauna, causes dilation of the veins in the legs, worsening this fluid shift. Everyone can feel a little faint if he/she gets out of a tub too quickly, and this feeling, orthostasis, is more pronounced in pregnant women.

I can think of many ways heat can harm the mother, but so far no one has linked to any study showing that heat can harm the fetus. Sea Legs, are there any, or are you picking out the negative studies only?

PiccolaPineCone said...

Come on SLG, you can't compare the rise in temperature during intercourse to the rise in temperature during exercise. The other day I measured my temperature at 39.7 deg C after a mile repeat session! [Insert joke here about my athleticism in bed but.... it's hard to believe temperature would get that high during intercourse unless one was doing it in one of your beloved saunas!]. It was not in the Clapp book that I read about sperm motility and temperature, it was in a variety of different studies. Here is one example of such:

"Sperm velocity increased steadily from zero to 50.4 nm/sec between freezing point and body temperature. Thereafter, their activity dropped dramatically and total immobilization occurred at 45°C."



"Semen specimens from fertile prevasectomy patients maintained at 4 degrees, 20 degrees, and 37 degrees C were evaluated at 3, 6, 12, and 18 hours after collection. Sperm viability, assessed by eosin-nigrosin stain, and motility decreased with time at 20 degrees and 37 degrees C, but at a significantly higher rate at 37 degrees C (where the motility was halved by 12 hours)."


High temperatures makes sperm slow!

sea legs girl said...

Cool PPC! More discussion. I love it.

Are these in vitro or in vivo studies? I'm just guessing in vitro, in which case they don't necessarily represent what happens in the human body. There is a reasonably wide range of temperature in which functions and reactions occur normally in the human body and I don't believe that exercise would under any sort of normal circumstances raise temperature to such an extent that it would significantly affect sperm transport. Showing that above a certain temperature sperm in a test tube move more slowly is not the same as a study showing that fertility is affected by the rise in body temperature caused by exercise. Hey - I'm not saying it's impossible, I just wouldn't believe it until I saw a more convincing study in women trying to conceive.

FB - I have seen one study where there is an association between a heat source and neurtal tube defects and that's the one I presented here. But is it the heat or something else about hot tubs or the women who visit them?

pernillesarup said...

I don’t know how fast the ramping speed of a fever compares to the convection of heat from a hot bath. I would think that the hot tub was faster a fever has to build up using excess heat from our own metabolism. But I know too little about how the human body thermo-regulates.

Concerning the studies on mental health and fever during pregnancy:
a) Correlations should always be interpreted with care. They do not prove a causal link.
b) Why do they think it is the heat (from the fever) and not the virus/bacteria causing the fever, or the immune response towards the pathogen, that causes the problem?

SteveQ said...

I won't pretend to have anything to say on the matter - but I did finally get the ø in your name in my blogroll!

Glaven Q. Heisenberg said...

Hi, slg - I just wanted to stop by and thank you for your kind words during this latest family tragedy of mine. So ... hey, thanks! I am hoping to be able to get back to blogging and commenting as before soon enough.

"As before" = "dickishly". But you knew that.

Also, congratulations on being the Rosa Parks of teratogens discussion. It's about time teratogens had a seat at the front of the bus. They'll have you to thank for it.

Oprah, on the other hand, would have bought them their own car. Just sayin'.

SteveQ said...

Have you heard "Go do" by Jonsi? It has all that nauseating pop stuff you like to run to.

SteveQ said...

I just read the new nutritional guidelines the government came up with here and searched to see what they had to say about weight gain in pregnancy. All it says is follow "Institute of Medicine and Nutritional Research Council's "Weight gain during pregnancy: re-examining the guidelines. Natl. Acad. Press, 2009." Well, that sure clears things up!