A new study has definitively shown that regular exposure to THC, the main psychoactive ingredient in cannabis, during pregnancy has significant impact on placental and fetal development -- led to a reduction in birth weight of 8 per cent and decreased brain and liver growth by more than 20 per cent.

I have to ask myself why people care about these things, and where the bias comes from.

I think this is a fascinating line of questions on this topic! There's a confluence of a few themes to consider: 1) First and foremost is the war on drugs, criminalization of marijuana and demonization of marijuana users

 a) deep seated mistrust of marijuana as a direct effect of decades of effective propaganda. As a personal anecdote - my grandfather was literally dying of cancer (many years ago, not an emotional plea) and was on significant amounts of opioids for a long period of time. He was getting lots of side effects - irritability, constipation, delirium etc... my family tried for years to get him to at least consider trying medicinal marijuana (it was legal there/then). He absolutely forbid anyone to bring him any because, in his words "he would rather die than become a drug addict"

b) renewed investment in this "war on drugs" in this particular moment in history as more and more states legalize recreational marijuana, the federal government hasn't made a move yet, Jeff Sessions had promised to "crack back down" on it. There's still some gop that seem to want to roll back the legal status of marijuana.

2)The identity of being pregnant and the forced expectation of "purity" during pregnancy. There's this very strong belief held by some that women who are pregnant need to sacrifice their personal needs and desires to meet the expectations of "being a mother". From this thread there's so much condemnation of women for not being able to "control themselves" for "just nine months". This appears to be justified by things like FAS. But the data behind FAS is very confusing. There's rat models that show beyond a shadow of a doubt that if you soak pregnant rats in booze, the babies get FAS. And there are higher rates of FAS in some populations that have higher alcohol consumption rates. but there are also lower FAS rates in some populations with higher alcohol consumption. In Europe it was always considered "ok" to drink a little during pregnancy, as opposed to the US where abstinence is emphasized. However we don't see significantly different rates of FAS between the two but some American's fervently hold this belief that you can't have any or else you're not a good mother. But the truth is that - like most diseases - there's a strong and as of yet undiscovered genetic/epigenetic component.

This becomes a deeply important public health topic when considering medications that mothers may need during pregnancy. There are many women who get pregnant who have chronic health conditions that require them to take medications that can cause problems for the fetus and a choice has to be made - the risk/benefit ratio has to be weighed. And it becomes difficult for a mother to make a choice in an atmosphere that is saturated with this "abstinence" culture built around morality as opposed to scientific evidence.

In the real world it comes down to that choice of "is it worth taking this 1mg thc every now and then to alleviate morning sickness or is it too much of a risk". Or for a mother with epilepsy... "is it worth continuing my medication and having a slight but known risk of severe illness in my child or is it better to risk injuring the fetus when I have an inevitable seizure from not taking my epilepsy medication" (fyi Medicine is 100% for taking the meds on this one). There are all these nuanced and difficult ethical and medical questions in this topic, and it's so frustrating when people try and simplify it to: "don't do drugs or you get a crack baby!"

/r/science Thread Parent Link - nature.com