conception dates

Can You Date Conception From Ultrasound Data?

Jane Foley's picture


Hi Ms. Ultrasound,

I hope you can help me with my question as it would really ease my concern.

I am 31 weeks pregnant; the first day of my last menstrual period date was 26 July 26, 2009 and my usual length of menstrual cycle ranges between 28 to 30 days.

I had unprotected sex on August 6th (Day 12) and August 17th (Day 23). I really need to know whether the baby was conceived on the 6th, or the 17th.

Here are the information of my early fetal ultrasounds:

Ultrasound and Conception Dates

Jane Foley's picture


Dear Ms. Ultrasound,
I have had two scans so far both match up with my lmp. I had one at 7 weeks and one at 13 weeks.
so I calculated that I conceived around 22nd September.

Here are my dates:
lmp: 9/10th Sept
28 Oct: 7 week scan
Conception around 22nd September?

However my period was very light and spotting, is it possible this was actually implantation and the ultrasound is out by few weeks?