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Dr. Andrew Rynne

Family Physician

Exp 50 years

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How to calculate the conception date and find paternity other than DNA testing?

Answered by
Dr. S Patra


Practicing since :2011

Answered : 4047 Questions

Posted on Tue, 5 Feb 2013 in Women's Health
Question: Trying to determine probable date of conception. Child born Oct 29 2007, Girl 8 lbs (3629gm). Ultrasound 6/16/2007 MA= 22w 0d. Ultrasound 9/16/2007 MA=34w 2 d. She thinks LMP was around first week of January, We were together exclusively XXXXXXX 14 to XXXXXXX 26 2007.
How likely I am the father? DNA testing not option
Answered by Dr. S Patra 1 hour later

Thanks for posting your query.

I have gone through your history in detail. I understand there is a paternity dispute and I hope the following information helps.

According to first ultrasound on 16th XXXXXXX calculated last menstrual period (LMP) date was around 13th January. That being said, ultrasound gives gross & detailed view on the basis of fetal maturity at the time of scan. But it is also known that development of fetus may be advance or small for date as in this case (first week of January - original LMP and 13th January - calculated LMP). Therefore fetal maturity may not always correspond with actual gestational age as calculated from original LMP.

In that respect, if the gestational age by ultrasound is within one week of the mother's LMP date, then we think it is within normal limit. Further maturity of fetus can be lagging behind the period of gestation in case of late scan.

On the other hand pregnancy depends on timing of unprotected sex and ovulation. Ovulation occurs approximately 14 days before next period due date (if previous cycle had been regular).

Therefore presuming her original LMP was around 1st week of January, then possibly the next due date was around first week of February and hence the ovulation could have occurred around 3rd week of January. As you were involved in regular sex around 3rd week of January (Jan 14 to XXXXXXX 26) on fertile period of your partner, it is likely that she conceived in the month of January and your possibility of being father is high enough.

If you still have doubts then you need to consider getting the DNA test which is superior to all investigation and gives the most reliable solution.

Hope I have answered your query and helped in determining probable time of conception. If you have any further questions I will be happy to help.

Wish good health for your family.


Above answer was peer-reviewed by : Dr. Prasad

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