 In light of our lack of knowledge of the teratogenic effects of most drugs, advice for pregnant women is generally conservative; women are advised to avoid medical interventions and medications during pregnancy if at all possible. For example, women with mental illnesses such as bipolar disorder and depression are often counseled to avoid medication during pregnancy, both because psychotropic drugs tend to diffuse readily across the placenta, and because typically, the mental state of the mother does not directly impact the health of the fetus (in contrast with, for instance, diabetes or life-threatening cancer). However, mental illness in pregnant women matters to fetal development: untreated depression, for example, is associated with premature birth, low birthweight, and other complications (Gold and Marcus 2008). Moreover, some researchers argue that evidence for negative health outcomes for children born from women taking anti-depressants is scant and unreliable, and provides little guidance for treatment (Byatt, Deligiannidis, and Freeman 2013, Pearlstein 2015). Without improved evidence, it is difficult to give any rules of thumb for the ethics of treating mental illness during pregnancy.