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Dr. Andrew Rynne
MD
Dr. Andrew Rynne

Family Physician

Exp 50 years

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How To Calculate The Actual Date Of Conception?

i had sex on the 21 of Feb then the 26. On Mar 5 i was spotting &on the 14 i found out i was pregnant. I looked online &it said implantation spotting occurs when your period is suppose to come. So a website tols me to count back 14 days from your expected period &it was the 21. Does this method really work?
Mon, 28 Sep 2015
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OBGYN,  's  Response
Hello and I hope I can help you today.

It is true that in a typical menstrual cycle, women ovulate about 2 weeks before they menstruate. However the egg can remain 72 hours in the reproductive tract, and sperm can live up to 5 days, so you do not necessarily conceive the day you have intercourse. So, give or take 5 days from your calculated ovulation date should be when you conceived. Doctors use the first day of your last period to calculate your due date because it is the only date we know for sure. Even ultrasound can be off as much as 5 days.

Regarding "implantation" bleeding, that does not happen to everyone and some women bleed a little when they ovulate, so that is really not a consistent reference to use in trying to figure out a conception date.

So when you have your first ultrasound for your pregnancy they will be able to calculate your due date and approximate your conception date. The earlier your ultrasound the more accurate it is.

I hope I was able to answer your question today and that this information was helpful.

Best wishes for your pregnancy, Dr. Brown
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How To Calculate The Actual Date Of Conception?

Hello and I hope I can help you today. It is true that in a typical menstrual cycle, women ovulate about 2 weeks before they menstruate. However the egg can remain 72 hours in the reproductive tract, and sperm can live up to 5 days, so you do not necessarily conceive the day you have intercourse. So, give or take 5 days from your calculated ovulation date should be when you conceived. Doctors use the first day of your last period to calculate your due date because it is the only date we know for sure. Even ultrasound can be off as much as 5 days. Regarding implantation bleeding, that does not happen to everyone and some women bleed a little when they ovulate, so that is really not a consistent reference to use in trying to figure out a conception date. So when you have your first ultrasound for your pregnancy they will be able to calculate your due date and approximate your conception date. The earlier your ultrasound the more accurate it is. I hope I was able to answer your question today and that this information was helpful. Best wishes for your pregnancy, Dr. Brown