Hello, thanks for using health care magic There are two important points i am considering for discussion; -the fact that serum hcg is low and and does not double every 48 hours adn -the fact that at 45 days after menses ( 5weeks ) there is no gestational sac. With the above,there are two main thoughts in mind -a previous miscarriage -a wrongly estimated age of pregnancy. However, the first seems to be more likely as a urine pregnancy test becomes positive at least at four weeks after previous menses adn a gestational sac is obvious if an endovaginal ultrasound is done. What you should do is consider having an endovaginal ultrasound and repeat serum hcg in a weeks time. Endovaginal ultrasound is very sensitive at early ages of pregnancy. Repeating the serum hcg in a week s time will say if the pregnancy is progressive or has stopped in case a gestational sac is seen. Serum hcg levels normally fall below detectable values at three weeks following a termination of pregnancy. The worst scenario will be if there is no gestational sac but the serum hcg continues to increase. This will imply there is an abnormal growth of trophoblastic tissue and prompt and appropriate management will be required. Hope this helps you. Best regards Dr Achuo