Fetal Growth Concerns: Understanding Ultrasound Measurements & Translocation History

Question
Hi. I have a history of miscarriages due to a genetic balanced translocation.  I had intercourse on July 4th (I am pretty sure) after an LH surge detected via OPK on July 3rd.  I just had my first ultrasound and measured 6weeks1day when I should be measuring (I think) six weeks 5 days.  
Would the 4 days really be an indicator of a problem given that I know my conception date?  My HCG levels are fine and I believe (but may be wrong) that my little boy measured small when he had his early ultrasound.  

Answer
Dear Jenny,

No - there is no reason to assume there is an issue at all. In general, ultrasonography dating of a pregnancy is more accurate than dating using the date of the mother's last menstrual period. The biometric crown-rump measurement (CRL) of the six to 12-week fetus provides the most accurate measurement - to approximately within three days of true gestational age. There is also the potential that, though the intercourse took place on 7/4 (you think), actual conception may have taken place in the few days after that - depending upon what date you ovulated on. Sperm cells can survive up to 5 days one past the cervix under ideal conditions. They simply swim around waiting for a viable egg.  :-)

I hope this has helped you and answered your question. I wish you well and congratulations!

Brenda