How do I calculate the age of my IVF pregnancy ?

Email this link to a friend.

A patient sent me this email

I had a query. I have conceived through IVF and ET was on Jan 6 th and my LMP was on Dec 20th.
I got my ultrasound done on 16th Feb and in scan it showed the pregnancy is 5 weeks 6 days.
If I calculate the growth of the baby from the date of the transfer, this seems fine, but if I calculate from the date of the LMP , it seems to be lagging behind.
I am completely confused - can you please help ?

This is a common problem, because IVF patients use their common sense and assume that doctors would calculate pregnancy dates based on the age of the embryo. Since they know the date of the embryo transfer, should the pregnancy be dated using this as the baseline.

However, doctors don't use embryonic age when dating a pregnancy in practise, because the clinical convention is always to use menstrual age !