Strengths and limitations
The present study provides novel evidence that women with COVID-19 are at a higher risk for PE at the first trimester mainly due to maternal risk factors, which are shared by both conditions. In addition, there does not seem to be an association between COVID-19 and risk factors for placental insufficiency. One of the main strengths of this study is the large number of subjects. Additionally, the first-trimester screening for PE was routinely performed; therefore, despite this being a retrospective study, maternal risk factors, PlGF and UtAPI were prospectively recorded for all patients at the time of the routine first-trimester scan.
One of the main limitations of this study is its retrospective nature. Additionally, this study may have a selection bias. On the one hand, cases in the study group with severe disease might be over-represented, as our site was a referral hospital for severe COVID-19 with pneumonia in Catalonia. On the other hand, asymptomatic cases in the study cohort might also be over-represented, since a RT-PCR was incorporated during the pandemic as a routine test for all admitted patients.
Another limitation of the study is that the general population used as the reference group cannot be considered purely a control group due to the lack of specific information about SARS-CoV-2 infection. For this reason, some asymptomatic and mild COVID-19 cases might be found in the reference group. Nevertheless, this might have reduced the chances of finding differences between groups making our findings even more meaningful.