Early Pregnancy Ultrasound Accuracy: Understanding Potential Discrepancies

Question
hi.. my name is katherine. i was wondering if you could help me. i had an ultrasound on oct. 2nd and it said i was 10 weeks 4 day, 10 weeks 6 days from my LMP(july 18th). my doctor told me my conception date was probably july 31st-aug 1st, is there any way i could have gotten pregnant in the beginning of july and the ultrasound is that off?? my cycles were 28-30 days. if you can help please let me know. please and thank you

Answer
Katherine,


No, an early ultrasound would not have been off that much.  Typically, they are accurate within +/- 2 days between 8-10 weeks gestation.  


Also, based on your typical cycle length, everything adds up correctly with your predicted ovulation and the ultrasound results.  If your cycle is typically 28-30 days in length, then ovulation most likely occurs between day 14-16 of your cycle, which is exactly what your ultrasound confirmed.



So, consider your doctor's estimation of when you conceived to be very accurate.



Best,
Catherine