Ans. b. USG for fetal cardiac activity (Ref: Dutta 6/e p68)Most accurate and safest method to diagnose viable pregnancy at 6 weeks is USG for fetal cardiac activity.Doppler is most sensitive but not safe in early pregnancy.Earliest diagnosis of pregnancy can he established safely by ultrasound for the fetal cardiac activity."An intrauterine gestational sac is reliably visualized with transvaginal sonography by 5 weeks, and an embryo with cardiac activity by 6 weeks. The embryo should be visible transvaginally once the mean sac diameter has reached 20 mm-- otherwise the gestation is anembryonic. Cardiac motion is usually visible with transvaginal imaging when the embryo length has reached 5 mm. If an embryo less than 7 mm is not identified to have cardiac activity, a subsequent examination is recommended in 1 week (American Institute of Ultrasound in Medicine, 2013a). "--Williams Obstetrics 24/e p196Most accurate and safest method to diagnose viable pregnancy at 6 weeks is USG for fetal cardiac activity.USG for fetal cardiac activity: At 6 weeks it is routine to detect fetal cardiac activity by ultrasound (and Doppler is not indicated).Doppler is most sensitive but not safe in early pregnancyDoppler examination of fetal vessels in early pregnancy should not be performed without a clinical indication- Ultrasound Obstet Gynecol 2011; 37:625-628Week 6 - Gestational Age (Fetal age 4 weeks)5 1/2 to 6 1/2 weeks is usually a very good time to detect either a fetal pole or even a fetal heart-beat by vaginal ultrasound.The fetal pole is the first visible sign of a developing embryo.The fetal pole now allows for crown to rump measurements (CRL) to be taken, so that pregnancy dating can be a bit more accurate.The fetal pole may be seen at a crown-rump length (CRL) of 2-4 mm, and the heartbeat may be seen as a regular flutter when the CRL has reached 5 mm.If a vaginal ultrasound is done and no fetal pole or cardiac activity is seen, another ultrasound scan should be done in 3-7 days.Human Chorionic GonadotrophinhCG is a glycoproteinIt consists of a hormone non-specific a and a hormone specific P subunitQ.It is chemically and functionally similar to pituitary luteinizing hormoneThe a subunit is biochemically similar to LH, FSH and TSH whereas B subunit is relatively unique to hCGHave highest carbohydrate content (30%) of any human hormoneFunctions of Human Chorionic Gonadotrophin* Rescue and maintenance of corpus luteum till 6 weeks of pregnancyQ* Stimulates both adrenal and placental steroidogenesisQ* Stimulates maternal thyroidQ because of its thyrotrophic activity* Immunosuppressive activityQ which may inhibit the matemal process of immunorejection of the fetus as the homograft* Stimulates Leydig cells of the male fetusQ to* produce testosterone in conjunction with fetal pituitary gonadotrophinsLevels of hCG:Production by syncytiotrophoblastQHalf life=24 hours. Doubling time=48 hours (2 days)QBy radio immunoassay detected in maternal serum or urine as early as 8-9 days following ovulationQ.Maximum blood and urine level 100-200 lU/ml between 60-70 days of pregnancyQDisappears from circulation within 2 weeks following deliveryQHigh levels of hCG is detected in* Multiple pregnancyQ* Hydatidiform mole or ChoriocarcinomaQ* Down's syndromeQ* Erythroblastosis fetalisQ resulting from maternal D-Ag isoimmunizationhCG is decreased in ectopic pregnancy and impending spontaneous abortion.