Perinatal mental illness has a significant implication on maternal health, birth outcomes, and the offspring's development. Prevalence estimates of perinatal psychiatric illnesses range widely, with substantial heterogeneity in different population studies, with a lower prevalence rate in high- rather than low- or middle-income countries. Because of the potential negative impact on maternal and child outcomes and the potential lability of these disorders, the perinatal period is a critical time to identify psychiatric illnesses. Thus, obstetricians and midwives play a crucial role in assessing women's mental health needs and to refer identified women promptly for multidisciplinary specialist assessment. However, there is still limited evidence on best practice assessment and management policies during pregnancy and postpartum. This review focuses on the prevalence of common perinatal mental disorders and antenatal screening policies to identify women at risk. The effect of these conditions and their management on pregnancy, fetal outcomes, and child development are discussed.