This study aimed to examine the pregnancy outcomes in women infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with and without underlying diseases in western Iran. This case-control study compared 49 pregnant women with Coronavirus disease (COVID-19) with underlying diseases (the case group) and 49 women with COVID-19 without underlying diseases (the control group). The groups were pregnant women with COVID-19 admitted to Hamadan hospitals for delivery. COVID-19 was diagnosed by using the reverse transcriptase-polymerase chain reaction (real-time RT-PCR). Data were evaluated using a checklist. Further, the Statistical Package for the Social Sciences (SPSS) version 16 was used for data analysis. A value of p<0.05 was considered statistically significant. The odds of preterm labor were five times higher in women with underlying diseases (OR=5.95, 95% CI (3.01, 7.15), p=0.034). Moreover, the odds of preeclampsia and eclampsia in women with underlying diseases was (OR=3.35, 95% CI (1.18, 4.93), p=0.048) and (OR=2.65, 95% CI (1.43, 3.54), p=0.035), respectively. The results revealed that preterm labor, preeclampsia, and eclampsia were significantly higher in women with COVID-19 and underlying diseases compared to those without underlying diseases. Thus, the need to identify and educate pregnant mothers on underlying diseases and attention to prenatal care, particularly in high-risk groups, is necessary for the COVID-19 pandemic.