Lateral just means to the side. There is no need to measure if there is a healthy heartbeat and a baby bouncing around. The size of the haematoma is (unless it is huge) mostly useless information. It doesn't really predict the volume of blood loss if you happen to bleed as some women re-absorb the clot and others pass it.

There is no specific need to rest if you are not actively bleeding. Prior to ultrasound this was probably a common and yet unidentified phenomenon. Women just bled - cause unknown. There is also no need for a c-section as there is no additional risk of placental abruption. I was a high risk pregnancy for both of my living babies and this was never suggested / mentioned / considered. HTH