Porsche-i had my BT 21 days after a day 3 TR so my embryo was 24 days old your embryos would have been 18 days old so a 6 day difference i was 5 weeks 5 days so i am guessing you would have been 4 weeks 4 days at time of BT so if you double your HCG every 2nd day your HCG would be around the 4000 mark around the same time i had my blood test so very similar to my number of 4759 and they suspected twins the nurse still thinks one could be hideing but we wont know until our 11.5 week u/s i just think it's one big strong boy growing in me.