She has been hospitalized with COVID-19 since birth, with postpartum…

She has been hospitalized with COVID-19 since birth, with postpartum bleeding and all in normal range. They discharged her with a good result. Today, at the 3rd ultrasound, everything is fine except for the placenta which has a problem. They force her to breathe oxygen via a mask, like oxygen deprivation, but it won't show anything. It's necessary for prophylaxis. Has anyone had this? Please tell me if it was common. Was there any history of an ultrasound showing everything okay, but the baby was born with hypoxia? Everything went well with the first one, but now I'm going crazy.