COVID-19 and pregnancy: a national registry based study Background: According to a cohort study involving 2,130 pregnant women from 16 countries, the impact of COVID-19 on maternal morbidity and mortality was higher in low- and middle-income countries. Other one study found that the coronavirus pandemic increased maternal mortality by 1.37 times. The COVID-19-related mortality risk is 3 times higher in pregnant women than in the general population. In our country, there is a lack of evidence that determine the impact of COVID-19 on maternal mortality based on the national registration system. We aimed to study the relationship between COVID-19 and maternal mortality and complications based on national registry data Materials and methods: The study was conducted between February 20, 2022 and March 1, 2022 based NCMCH. The impact of the coronavirus pandemic on maternal mortality was performed based on the 2020-2021 maternal mortality data of Mongolia through a retrospective and time series analysis. In order to estimated factors that affect the complications of a pregnant women’s COVID-19 infection, it was conducted a retrospective study design based on the database of pregnant women diagnosed with a COVID-19 infection. The study data was collected through a prepared questionnaire. Results: According to analysis, the maternal mortality rate in Mongolia in 2021 was 1.9 times higher than the predicted rate. In 2021, 67.6% of maternal deaths are due to COVID-19. In 2021, the maternal mortality rate due to Covid-19 was 64.2 per 100,000 live births, which is twice as high as maternal mortality due to other diseases. In 2020-2022, 17,789 pregnant women between the ages of 14 and 46 who were infected with the coronavirus were included in the study to determine the factors affecting the complications of COVID-19. The mean age of the participants was 30 ± 5.8 (95% CI 29.7 – 29.9) and their gestational age was 24 ± 10 weeks. Of all participants, 71.6% was diagnosed and treated in Ulaanbaatar. 52.7% of pregnant mothers diagnosed with coronavirus and presenting with complications have not been vaccinated, which is a relatively high rate compared to the group of pregnant mothers without complications. Not being vaccinated against coronavirus had a 70% increased risk of complications (OR = 1.7, 95.0% CI: 1.4–2.0). However, the probability of hospitalization increased by 20% (OR = 1.2, 95.0% CI: 1.0 – 1.4). The COVID-19 severity depends on the age of the maternal and the length of the pregnancy. Conclusion: The COVID-19 pandemic has had a significant impact on maternal mortality, has increased. The maternal mortality rate in Mongolia is low compared to other countries, but it is higher than the recommended level for reducing maternal mortality. COVID-19 vaccination, on the other hand, reduced the complications of pregnant women and had a protective effect. It is important to build evidence by examining the effects of COVID-19 and vaccines on pregnant women.