Asymmetry of the lateral ventricles

During my anatomy u/s at week 21, I was told that the left ventricle is 7.2 and then right ventricle is 8.8 and is getting near the borderline of normal which is considered 10. I was asked to return two weeks later for an additional u/s, at which the right ventricle was measured at approx 10. I was instructed to have an MRI which I did yesterday. According to the MRI report: the right atrium measures approx 9.4 to 10.1 mm in greatest dimension. There is no evidence of gross cortical abnormality, intracranial hemorrhage, or infarction. (I should also mention that I had a CVS which was normal).
My OBGYN says there is nothing to be concerned about. But I don’t understand, if the ventricle grew from 8.8 to approx 10 in two weeks how do we know that it won’t continue growing and become a problem?
Toda Raba for taking the time to read and response, Mor