What exactly is a diagnosis of a "poor fetal growth - antepartum" (65653) (ultrasound)? - fetal growth pictures

My wife was 2 months pregnant and want an ultrasound, but written for the diagnosis of OGBYN ultrasound is "lack of growth of the fetus - before birth, code 65653rd What exactly that, and we should be worried?" The doctor says everything is "good" but we have doubts as to believe him. Thank you.