Women of childbearing age appear to be particularly susceptible to the exacerbation of existing mental illness and the development of new mental illness [
1–
5]. Indeed, it has been estimated that over 500,000 pregnancies annually are complicated by psychiatric illness that either precedes pregnancy or arises during pregnancy [
6]. Untreated psychiatric disease during pregnancy is associated with increased risks for the mother (including self-harm/suicide, self-neglect, and reduced compliance with prenatal and postnatal care) and risks for the child (including impaired fetal development, infanticide, and impaired mother-child bonding) (reviewed in [
7,
8]). Historically, antipsychotics have been extensively and effectively used for the treatment of schizophrenia and bipolar disorder, and more recently they are becoming part of the treatment of depression [
9–
12]. Conventional antipsychotics (also known as typical or first generation antipsychotics) which were more commonly used to treat these conditions caused a significant decrease in fertility [
13]. However, the newer atypical antipsychotics do not have this side-effect. As a consequence, the number of women taking antipsychotics, who are becoming pregnant, is on the rise. Indeed, appointments at a Motherisk Program Clinic related to the use of antipsychotic medications increased 170% between 1989 and 2001; a rise which was for the most part attributable to an increased use of second-generation or atypical antipsychotics [
14]. The vast majority of women who use antipsychotics during pregnancy do so because of ongoing illness. In fact, only in cases of where the first schizophrenic episodes [
15] are reported in pregnancy or there is a risk of puerperal psychosis [
16] would the exposure of antipsychotic exposure be restricted to the pregnancy period.
Functionally, typical antipsychotics exhibit high affinities for D
2 receptors [
15,
17] in the mesolimbic, mesocortical [
16], and nigrostriatal dopamine pathways. This, rather nonspecific targeting of dopaminergic pathways, can result in a range of undesirable motor disorders [
18]. Atypical antipsychotics, however, are more selective for the D
2 receptors in mesolimbic pathway as compared to those in the mesocortical and nigrostriatal pathways. In addition, they also target the serotonin receptor subtype 2A (5HT
2A) [
19] which may help to reduce the negative side-effects associated with typical antipsychotics [
19,
20]. It is important to note that the proper correlation between the ratio of the clinical dosage and D
2 receptor affinity necessary to treat the symptoms of conditions such as schizophrenia has not been completely established [
21].
It is well understood that the suitability of antipsychotic medications during pregnancy is a balance between the risks of adverse obstetrical and neonatal outcomes and the risks associated with untreated or inadequately treated psychiatric illness. The most common atypical antipsychotics administered during pregnancy are Olanzapine, Clozapine, Risperidone, Quetiapine, and Aripiprazole [
22]. Complicating the matter further is that almost 40–57% of women taking atypical antipsychotics during are prescribed a combination of these drugs (polytherapy) [
23–
25]. In general, current practice guidelines discourage changing medications during pregnancy as this may leave the patient on nontherapeutic doses during a period of time; a situation which is not in the best interests of the mother. Therefore, the usual standard of care dictates that dosages be increased or polytherapy be implemented.
Although general clinical practice guidelines have been established (ACOG, 2008) [
9], there remains significant uncertainty regarding effects of these drugs on the fetus. To date, the teratogenic effects of antipsychotic exposure have received significant attention; however, the effects of these medications on long-term health outcomes of the offspring have not been well studied. In adults, one of the major side-effects of antipsychotic use is the dysregulation of body weight homeostasis (reviewed in [
26,
27]). Similarly, maternal use of antipsychotics has been reported to result in aberrant fetal growth. Indeed maternal antipsychotic use has been reported to result in an increased incidence of both low and high birth weight relative to the general population [
23,
24,
28,
29]. Since being either too small or too large at birth is a risk factor for the development of metabolic syndrome in postnatal life [
30–
32], children exposed to antipsychotic medications
in utero may be at increased risk of developing obesity in postnatal life. However, there are no human studies which have tested this hypothesis and the mechanism(s) by which atypical antipsychotics may affect fetal growth have yet to be elucidated. It is very difficult to decipher, based on the available literature, why atypical antipsychotics can cause both small for gestational age (SGA) and large gestational age (LGA) fetuses. For example, McKenna et al. [
23] report an increased risk of SGA in women taking the atypical antipsychotics Olanzapine, Risperidone, Quetiapine, and Clozapine. In contrast, Newham et al. [
24] report an increased risk of LGA for women taking the atypical antipsychotics Amisulpride, Clozapine, Olanzapine, Quetiapine, and Risperidone. Since the sample sizes in these studies are small for women taking each of the individual drugs, the risks associated with each drug cannot be accurately reported. Furthermore, the paucity of data evaluating the action of antipsychotics in pregnancy using animal models makes the discussion of mechanisms for these drugs difficult.