Mothers of children with FASD report higher levels of alcohol consumption by their partner, family and friends [
17,
34]. Ceccanti et al. found that alcohol problems in the family increased the likelihood of having a child with FASD by nine times [
63]. Alcohol use by friends and family may impact on PAE in various ways. First, the drinking behaviour of those in close social networks may represent the norms within that context. For example, a binge pattern of drinking may be viewed as less problematic in some communities in South Africa where heavy episodic alcohol use is commonplace [
132]. Second, some women may feel coerced into drinking before and during pregnancy as a result of the behaviour of friends and family. In a study of mothers of children with FAS, Astley et al. reported that 36% of women said that they did not want to reduce their prenatal alcohol intake because their partner did not want them to, and 20% because their family and friends did not want them to [
134]. Strong correlations between maternal substance use and the substance use of friends and family could also be due to processes of self-selection, in which individuals pick companions who are similar to themselves and who support their behaviour [
190]. In the DAG, we represented this mechanism via the unspecified ‘risky behaviour’ node that influences both maternal substance use and choice of social network. Finally, as described above, mothers of children with FASD are more likely to have symptoms of FASD themselves and to report that the maternal grandmother has a history of alcohol problems [
32,
59]. This raises the possibility of intergenerational transmission of FASD, a phenomenon that has received support via controlled animal studies [
191]. Heavy alcohol use by the maternal grandmother could indicate the presence of a risk genotype for heavy alcohol use [
192], could result in epigenetic changes that increase the risk of heavy alcohol use in later generations [
191] and could provide a model of problematic alcohol use that is adopted by offspring via social learning [
193]. Recent evidence from animal studies suggests that paternal alcohol consumption could influence the epigenetics of sperm DNA by influencing methylation patterns in sites that are important to developmental outcomes [
194]. Paternal alcohol use has been associated with FASD symptomology including low birth weight, reduced brain size, microcephaly, impaired learning and hyperresponsiveness [
42,
195], although results have been inconsistent [
196].