Most accurate method to detect pregnancy at 6 weeks gestation is:

Ref: Williams Obstetrics, 23rd edition and Daftary's Manual of Obstetrics, 3rd editionExplanation:"Most accurate and safest method to diagnose vi- able pregnancy at 6 weeks is USG for fetal cardiac activity. " Ref: DaftarvFetal 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 should not be performed without a clinical indication. (Ref: Ultrasound Obstetric Gynecol 2011; 37: 625-8)TAS can detect the fetal parameters in the following sequences:o Gestational sac - 4-5 weeks of menstrual age.o Fetal pole - 6th weeko Fetal cardiac activity-7th weeko CRL - 7th week.TVS detects the parameters l week earlierHUMAN CHORIONIC GONADOTROPHIN (HCG)Glycoprotein.Have highest carbohydrate content (30%) of any human hormone.Functionso Rescue and maintenance of corpus luteum till 6 weeks of pregnancyo Stimulates Ley dig cells of the male fetuso Immunosuppressive activity - Inhibits maternal process of immunorejection of the fetus.o Stimulates both adrenal and placental steroidogenesis.o Stimulates maternal thyroid - due to thyrotrophic activity.Levels of HCGo Produced by Svncytiotrophoblasto Half life - 24 hours; Doubling time = 48 hours (2 days).o By radio immunoassay detected in maternal serum or urine as early as 8 - 9 days following ovulation.o Maximum blood and urine level: 10(1 - 200 IU/ml between 6b - 70 days of pregnancyo Disappears from circulation within 2 weeks following delivery.HCG is also increased ino Multiple pregnancy.o Hydatiform moleo Choriocarcinomao Down's syndrome,o Erythroblastosis fetalis.HCG is decreased in:o Ectopic pregnancy.o Impending spontaneous abortion.DIAGNOSIS OF PREGNANCY BY DIFFERENT TESTSRadioreceptor assay - 22nd day of cycle (Earliest).Radioimmunoassay - 25th day of cycle.ELISA - 1st day of missed period.Velocity card test - 2-3 days after missed period.Beta gravindex test - 2 days after missed period.Latex agglutination test - 42 days after LMP.