When I was pregnant with twins, the neonatologist did an ultrasound and found that one of the babies had an enlarged ventricle on one side of his brain. They called his condition "mild unilateral ventriculomegaly". (I am answering your question based on my belief that the excess fluid which doesn't drain properly is the cause of the enlarged ventricle.) I had to go in for frequent ultrasounds so they could monitor the ventricle. With the newest technologies (this was almost 12 years ago) they said that they can see so much more than ever before, that there are much more worries nowadays and that it probably would resolve itself. When he was born at 36 weeks, they did an ultrasound through his fontanel which showed that the ventricle was still mildly enlarged. They really weren't concerned but still wanted me to bring him back before his first birthday so they could do another ultrasound. At this point, the ventricle was slightly bigger than the upper range of normal. They didn't think there would be any problems, and in fact, there hasn't. He's now a cuddly bookworm, math whiz, history buff. (If the ventricle was larger, they said it could be rectified by a shunt which would help it drain. Supposedly there are lots of kids with shunts and they can even go swimming without any problems. Who knew?!) I know that only a piece of my story aligns with yours, but I hope it's helped in some way. This is a very difficult time for you, especially not having a diagnosis. Things will probably be fine, but in the meantime, my prayers will be with you and your precious baby. Blessings.