My Daughter Is 27 Weeks Pregnant And Is Going To

My daughter Is 27 weeks pregnant and is going to a specialist because the baby has fluid in her belly, it 1st started in her lung then moved to the belly.Today she had another ultra sound and the fluid has gotten larger. they want to see her in 1 week and said come prepared with a bag in case they put her in the hospital to try to withdrawl some of this fluid. All of the blood work is good and her growth is good. I am concerned about what I read about Hydrops Fetalis it does not sound positive. The doctor seems baffled because it is only one area with fluid. Can you give me some insight on this matter?