The effect of marijuana on developing fetuses

This has been something that has been coming up in conversation with my friends lately. Everyone is vaguely in agreement that smoking pot is definetly not the worst thing you can do to a fetus, at least not as bad as cigarettes, alcohol, crack, etc. This is hardly a definitive answer, however. And, no, I don't plan on smoking pot during my pregnancy, BUT, I also resent the way that pregnant women are advised to not do this or that, and we are expected to believe it based on some sort of pseudo-religious faith in the authority of doctors. So, I have embarked on a mini-research project concerning the effects of marjuana usage on the development of a fetus and the outcomes for the child later in life. (This topic has suddenly become much more interesting than writing about microglial regulation and cognitive changes with age, my thesis, I mean.... I suspect this is probably a complex procrastination scheme that my brain is cleverly justifying to myself. But I can't help myself).

What's intersting about this topic is that, similar to the alcohol and pregnancy post from a few weeks ago, there are surprisingly few controlled studies done on this topic. It's very difficult to find studies where the women were only smoking pot. This makes the statistics difficult to interpret. For example, Marroun et al. published a study last month in Drug and Alcohol Dependency reporting that marjuana use during pregnancy resulted in increased externalizing behavior problems (i.e. aggressive behavior and attention problems) in 18 month-old babies. What's nice about this study, is that they had a very large population sample- 4077 children with the associated data from the parents in the Netherlands. They interviewed the mother and father in the 1st trimester then again shortly after birth and then one more time when the child was 18mo. Out of the 4077 children, 88 were exposed to cannabis prenatally. Of babies exposed to cannabis, 84.5% were also exposed to tobacco throughout pregnancy. That's a lot! This means that only 13.64 children were exposed to cannabis, exclusively, during pregnancy out of 4077 kids! They couldn't do useful statistics on a group this small. On the other hand, 276 children were exposed to tobacco exclusively throughout pregnancy. The other two groups that made up the bulk of the study population were early exposure to tobacco (435), and no cannabis/tobacco use (3278). Here's the thing, the exact same increase in aggressive behavior problems seen in the cannabis exposed group was seen in children who were exposed to tobacco-only throughout pregnancy! Specifically, aggressive behavior and attention problems were found in 13.0 +/- 6.5% of the cannabis(and tobacco) exposed group, and 12.7 +/- 6.6% of the tobacco-only group compared to about a 10% incidence in the other two groups. This means that all of the effects that the authors are attributing to cannabis could be explained by tobacco exposure, so it's puzzling that they entitled this study, "Intrauterine cannabis exposure leads to more aggressive behavior and attention problems in 18 month old girls". Shouldn't the title say "cannabis/tobacco",  or even, "Intrauterine tobacco exposure"? At least one other study found profound changes in the behavior of 3 year old toddlers in mothers that were heavy tobacco smokers (Day et al, J Dev Behav Pediatr. 2000 June; 21(3)180-8), so this conclusion would make sense.

The decision of the authors to make this the title of the paper and make this the primary conclusion of the study seems, ummm.... irresponsible.... it's just not the conclusion that's supported by the data that they show. Based on their data, they could have concluded with just as much confidence that cannabis exposure caused nothing. I can't help but to think that this seems oddly politically motivated. Perhaps they reaaaalllyy wanted their results to be consistent with previous studies that show increased aggressive and attentional problems in older school-age children and adolescents who were exposed to cannabis prenatally (Fried et al. Neurotoxicol Teratol 1992, Sept-Oct(5) 299-311; Day et al, Neurotoxicol Teratol 1994, March-April (2)169-75). These studies are fraught with confounding factors as well though! I'll spare you the full statistics discussion, but in most cases the women were also almost definetly smoking cigarettes, and often using a bunch of other street drugs, not to mention a variety of other confounding factors. Women who smoked pot while they were pregnant tended to be less educated, minority, low economic status, and had a higher incidence of violence in the home before and after the child was born. All these things are very difficult to control for, but it is possible that intrauterine cannabis exposure may be the least of these children's problems. It's important to mention too, that not all studies found negative effects of marijuana consumption, some found no effects at all (Tennes et al, Current Research on the Consequences of Maternal Drug Abuse, 1985 No.58 and Richardson et al, Infant Behav Dev., 1989;12: 199-209).

(*note* most of these reports are based on questionaires and there is probably more than a little bit of dishonestly going on. Some studies tested blood samples, or the baby shortly after birth, and found inconsistency with what the women were saying compared with the biochemical tests. Perhaps the women who admitted to smoking marijuana only did so because it was the most innocuous drug they were using. That's speculative, though)

There are a series of studies done by Melanie Dreher that I find sort of interesting. These studies are done in Jamaican women living in rural communities, so there is a really interesting cultural context that contributes to these studies. You can read in detail what she has to say in this interview if you want. I'll sumarize briefly here. Basically, the use of marjuana (or 'ganja' as it is called in Jamaica) is governed by a set of cultural guidelines that regard use as a special ritual with a certain way you're supposed to act. This has the effect of preventing abuse. Ganja is smoked mostly by men and the men are expected to discuss current events and remain composed while under the influence (women are not considered to have the "right kind of brain" for ganja smoking. So it is not generally considered appropriate for women to smoke, but was by no means uncommon. In fact, a small group of women called "root's daughters" smoked ganja openly with the men and tended to be more educated and to apparently "have the right kinds of brains" for ganja smoking) . There are also folk beliefs about the health benefits of ganja, and it is widely consumed as a tea by men, women and children of all ages, often in the morning to help with the days work and promote well-being. All of the women that did use ganja during pregnancy believed that it was very healthy for them and for their growing baby. This is in contrast to our culture where marijuana use is mostly recreational... oh, and and its illegal... (I almost forgot).

In most of the studies discussed above, which were done in North America or Europe, a major confound was the use of multiple drugs. The big advantage of this study was that in Jamaica, the women who did use ganja were much more likely to use it exclusively because alcohol and tobacco use was very rare. Also, because this research took a medical anthropology approach to this study, the researchers had a lot of contact with the women, even visiting them in their homes relatively often. This likely reduced the occurence of dishonesty that is inherent in questionaire approaches.

Dreher et al. (Pediatrics. 1994;93:254-260) studied 33 users and 27 non-users of ganja. The mothers were interviewed and observed multiple times during their pregnancy and the children were examined 1 and 3 days after birth, then again at 30 days, using a common measure of infant health, the Neonatal Behavioral Assesment Scale (NBAS). The authors found that at 30 days postnatally, the babies of the ganja users showed significantly increased scores on autonomic stability and reflexes. Also, the babies of heavy ganja users showed more rapid habituation to auditory and visual stimuli, a higher degree of alertness, and a greater degree of consolability (i.e. less irritable). The authors point out that these effects may not be attributed solely to the ganja usage, but may have more to do with the social status of the mothers who tended to use ganja more often. In contrast with the studies above, the women who used ganja heavily were the most educated of the group (the root's daughters that I mentioned above). In addition, the heavy users also tended to be more financially independent and less reliant on the father for support.

So finally, what I think all this is telling us, is that it doesn't really matter if you smoke some pot or not (Think of all the children born during the 60's and 70's that turned out to be just fine). It is the type of situation the pregnant woman is in, and the situation that the child is born into, that determines the emotional and psychological health of the baby. It seems that secure financial situations and relatively high levels of parental education make a big difference in how the child does.

With that said, there isn't really enough information to figure out the (apparently very subtle) effects of marjuana usage during pregnancy, which is why women are generally advised not to smoke and I guess that's a pretty good guideline. I'm just trying to point out that there is a lot more to the story and humans are very complicated...... animals studies can solve some of those problems. There are some studies done in rats and mice that were exposed to marijuana prenatally that show some changes to emotional processing, but that's a whole other very long story with a whole other set of problems (for example, getting the rats to smoke those tiny joints...)