My sis 4.5 months pregnant w 6 cent cyst on ovary. what should she do? worry she pass out from pain and low bp if it ruptures.

Observe: The cyst may resolve on its own. It is true it may rupture and/or cause pain, but these things may not happen. If the pain becomes unbearable an operation may be done while pregnant to remove it. Otherwise an ultrasound may be done 6 weeks postpartum to check on it. It may be gone by then. If not, her doctor may have some suggestions including surgery.