Q. How to find the exact date of conception?

Answered by
Dr. Kamalpreet Kaur Nagpal
and medically reviewed by iCliniq medical review team.
Published on Jan 27, 2017 and last reviewed on: Oct 09, 2018

Hi doctor,

According to my LMP, I was 9 weeks and 5 days pregnant, and ultrasound showed I was 9 weeks and 3 days pregnant. There was a CRL measurement of 26.96 mm. I had sex on the last day of my periods and then again after 11 days. And, my LMP and ultrasound calculation show two days difference. So, can I tell that I pregnant on the second event? My periods are irregular. The previous month, I also had endometriosis surgery. I have heard that endometriosis surgery can cause high fertility and regular ovulation. Since my LMP and ultrasound are close enough, is it safe to say ovulation was normal at least for that month?

Dr. Kamalpreet Kaur Nagpal

Obstetrics And Gynaecology


Welcome to icliniq.com.

Your estimation is correct. There is the least possibility of conceiving on the last day of the period. You must have conceived around the second event.

Now, LMP (last menstrual period) and ultrasound time cannot match exactly. Although in your case, it is almost the same. Do not confuse about two days difference.

Ultrasound calculates the period of gestation according to some measurements as you have seen CRL (crown-rump length) at different periods and separate parameters for calculating the time of gestation.

Now, LMP also cannot tell you exactly the day of ovulation until unless ovulation study was done and you have seen the size of the follicle and then its rupture to release the egg.

Usually, early scan done at six weeks or so is the best predictor of your dates. But, now also, everything is fine, and you can monitor growth in further scans.

For further information consult an obstetrician and gynaecologist online --> https://www.icliniq.com/ask-a-doctor-online/obstetrician-and-gynaecologist

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