Depression is a common and complex disease, influenced by both genetic and environmental factors, with heritability estimated to be from 31% to 42%. However, a recent genome-wide association study meta-analysing data on 807,553 individuals from three largest GWAS studies identified 102 independent variants and 269 genes associated with depression. This result suggests that depression is a polygenetic trait and enables researchers to use these polygenic risk scores to investigate how genetic liability for depression manifests over the life course.

Depression is more common in women during childbearing age, but it has particular importance during pregnancy and after birth due to additional potential consequences for the child. There are many women worldwide suffering from perinatal depression, and according to a meta-analysis, the prevalence of it ranges from 6.5% to 13% at different time points during pregnancy. Perinatal depression has been reported to be associated with many complications, such as hypertension, preeclampsia, and gestational diabetes for mothers and premature birth, low birth weight, fetal growth restriction for foetuses. Furthermore, some pregnant women with depression are reported to have suicidal ideation and thoughts of harming their child. It is clear that perinatal depression is important for both the mother and the child, and thus it is important to examine its aetiology in order to identify potential treatments and interventions. The role of genetics in perinatal presentation of depression is one particular path that could further enhance our understanding of the disease.

There are many studies on heritability of depression, but few about the genetic architecture of perinatal depression. This study will use the polygenetic risk score based on GWAS study on broad depression and examine the association between greater genetic liability to depression and depression across the perinatal period.