Background: While the Swedish maternal health care system has been an enormous success, and maternal and neonatal mortality and morbidity rates in Sweden are among the lowest worldwide, the added complication of ongoing coronavirus disease-2019 (COVID-19) pandemic may challenge the services that the health care system can provide. Health consequences during pandemic can be enormous, and not the least the effects on mental health. However, the effects of an active pandemic on parental mental health are not well understood, although recent international reports point at an urgent increase in symptoms of mental ill-health implying risks also for the unborn children. Aim: To investigate the impact of the COVID-19 pandemic on the mental ill-health of pregnant and postpartum women in Sweden. The research questions are (1) if there has been a change in the incidence of perinatal mental ill-health-related outcomes between the years 2014-2019 and after the COVID-19 pandemic outbreak in Sweden in 2020, and (2) if confirmed or suspected infection with COVID-19 in pregnant women or new mothers is associated with a higher risk for later development of negative mental ill-health related outcomes. Methods: National register study with data from pregnant and postpartum women with a delivery date or expected delivery date from January 2014 until latest possible date (end of 2021) Data are obtained from the Swedish Pregnancy Register (PR), the Swedish Register of Communicable Diseases (SmiNet), the Swedish Medical Birth Registry (MBR), the Swedish Prescribed Drug Register (PDR), the Swedish Cause of Death Register (CDR), and the Register of the Total Population (RTB). For aim 1, four categories/subgroups of women will be identified: 1) Early pregnancy (week 1 to 22), 2) Late pregnancy (week 23 to delivery), 3) Early postpartum (month 1 to 3 postpartum), and 4) Late postpartum (month 4 to 6 postpartum). The exposed group in each of the four categories will be women entering the respective perinatal category period from March 1, 2020. The remaining women will constitute the non-exposed group. Outcomes considered are new diagnosis of psychiatric disorders or self-harm, new redeeming of prescribed medication for psychiatric disorders and pain syndromes, mortality from unnatural causes, and women’s own self-reported general and mental health. For aim 2, women obtaining a COVID-related diagnosis during the above given perinatal period (exposed) will be compared to non-exposed women during the same period, concerning outcomes related to mental ill-health. All subjects will be observed from their entry in the study until outcome, emigration, death, or end of the study period (nine months from entry), whichever occurs first.