How accurate is conception dating
The tendency for multiple gestations to be delivered earlier than singleton pregnancies should not be interpreted that multiples should be assigned an earlier estimated due date.
Time of implantation of the conceptus and loss of pregnancy. Human Chorionic Gonadotropin Pregnancy Test Human chorionic gonadotropin first becomes detectable in the mother's blood and urine between 6 and 14 days after fertilization (3 to 4 weeks gestational age) [11-13]. The gestational age would, therefore, be at least 3 to 4 weeks at the time of a reliable h CG pregnancy test. Berghella V, et al., Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies? American College of Obstetricians and Gynecologists.