Had 19 week sonogram and was told the head wasn't closed?

A babies head has different plates that are not fused together. If your doctor was not alarmed then you should not be either. When your baby is born he/she will have two soft spots (one in the back and one in the front). These soft spots is where the head is not closed yet. There is thick tissue to protect the brain but it is not yet bone. The one in the back of your babies head will close first and then the one in the front of his/her head. I hope this helps and congrats on your pregnancy.