Dear ,dont worry Hydronephrosis  is not infection ,may cause because Usually due to malformation of ureter or ureter block or block at ureter vascular junction can cause ,based on nephrosis  if for to come full dry differences maintenence plus then urological surgeon can perform can perform some assistance . Now u don't worry , deliver baby and  may few months later it may recover or may need surgical intervention  based on degree of  hydronephrosis  , Usually to block aid of ureter out let or mal formation , If uv reflex is cause then usually resolved later  U wl get best answer after delivery ,meet pediatrics urologist