Most accurate method to detect pregnancy at 6 weeks gestation is

"Most accurate and safest method to diagnose ble pregnancy at 6 weeks is USG for fetal cardiac activity." Ref: DaftaryFetal cardiac activity by Transvaginal USG can be picked as early as 6 weeks.Fetal cardiac activity by Transabdominal USG can be picked as early as 7 weeks.Doppler is most sensitive but not safe in early pregnancy.Doppler examination of fetal vessels in early pregnancy shouldn&;t be performed without a clinical indication. TAS can detect the fetal parameters in the following sequences:Gestational sac - 4-5 weeks of menstrual age.Fetal pole - 6th week.Fetal cardiac activity 7th week.CRL - 7th week.TVS detects the parameters 1 week earlier.(Refer: William's Obstetrics, 23rd edition)(Refer: Ultrasound Obstetric Gynaecology 2011; 37: 625-8)