Best investigation to diagnose fetal age is:

A sonographic examination offers vital information regarding fetal anatomy, physiology, growth, and well-being. Ultrasounds are safe: Transducers used in obstetrics contain groups of piezoelectric crystals. These crystals conve electrical energy into sound waves. Hence, there is no exposure to harmful radiations, in contrast to X- rays. Though there are 'Sinlge best parameters' for all three trimesters to asses gestational age i,e. CRL for 1st trimester, BPD for 2nd and 3rd trimesters, but perfect estimation of the gestational age is best done with a composite assessment of all fetal parameters. Amniocenetesis has a risk of aboion(aboion rate <1%)