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Dr. Andrew Rynne
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Dr. Andrew Rynne

Family Physician

Exp 50 years

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How To Calculate The Date Of Conception?

Hello. I am around 11 weeks pregnant and am trying to figure out when I conceived and hence who the father of my child is. My last period was towards the end of Sept. Not sure on exact dates however. I had unprotected intercourse on the 4th of Oct with partner#1. Protected sex on Oct 11th with partner#2. And then unprotected sex on the 17th of Oct with partner #3. My first ultrasound put me at 5w5d gestation and estimated my conception on Oct. 11. but my second ultrasound put me at 9w4d and estimated my conception on Oct. 14. I know its a slight difference. But with this information. Margin of error, lifespan of sperm, and any other variables. Who would most likely be the father??? Thanks
Fri, 8 Jan 2016
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Pathologist and Microbiologist,  's  Response
Hello and welcome to HCM,
The day of conception lies around the day of ovulation.
In a regular 28 day cycle, ovulationntakes place 14 days prior to onset of menstruation.
Assuming that you have regular menstrual cycles and end of September to be your menstrual cycle, the day of ovulation should be somewhere mid-October.
Conception took place either on October 11 or 17.
Taking the first day of menstruation as the day 1 of menstrual cycle, you can determine the likely day of conception.
If your cycles are regular 28 day, October 11 is more likely.
However, if you have longer cycles, October 17 is a possibility.
However, ultrasound findings are more likely to correlate with conception date.

Thanks and take care
Dr Shailja Puri
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How To Calculate The Date Of Conception?

Hello and welcome to HCM, The day of conception lies around the day of ovulation. In a regular 28 day cycle, ovulationntakes place 14 days prior to onset of menstruation. Assuming that you have regular menstrual cycles and end of September to be your menstrual cycle, the day of ovulation should be somewhere mid-October. Conception took place either on October 11 or 17. Taking the first day of menstruation as the day 1 of menstrual cycle, you can determine the likely day of conception. If your cycles are regular 28 day, October 11 is more likely. However, if you have longer cycles, October 17 is a possibility. However, ultrasound findings are more likely to correlate with conception date. Thanks and take care Dr Shailja Puri