<prompt> Detailed survey for fetal anamolies is done at what period of gestation?12-14 weeks14-16 weeks16-18 weeks18-20 weeks  <response>: Ans. is d i.e., 18-20 weeks Transvaginal ultrasonography Gestational sac and yolk sac - 5 menstrual weeks Fetal pole and cardiac activity - 6 weeks Embryonic movements -7 weekso Fetal gestational age is best determined by measuring the CRL between 7 and 12 weeks variation - 5 days.o Doppler effect of ultrasound can pick up the fetal heart rate reliably by 1 Oth week.o Routine sonography at 18-20 weeks permits a detailed survey of fetal anatomy, placental localization and the integrity of the cervical canal. 