Hello Doctor I M Farahan ,i Would Like To Know

Hello doctor i m Farahan ,i would like to know my wife is 33 weeks 2 days pragnant. In ultrasound is showed that head circumference is 288.4 mm. HC> 3%. It's means she is 3 weeks behind. My doctor told me not to worry. But doctor hasn't given me any medicine as she asked us to ultrasound every week. Do I need to worry ? Thank you