Girl, hi! Today I had an ultrasound at 2 trimesters, they couldn't see…

Girl, hi! Today I had an ultrasound at 2 trimesters, they couldn't see the 4-chamber heart again, only the 3-chamber, with the baby everything is good, heartbeat 152 bpm. Ultrasound at 17 weeks also didn't see it, now 20 weeks and 5 days. Who has encountered such a situation? Excused for errors in Russian, if I wrote them wrong)