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Dr. Andrew Rynne
MD
Dr. Andrew Rynne

Family Physician

Exp 50 years

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How Can Exact Conception Dates Be Estimated?

My girlfriend is pregnant. We recently had an ultra scan (Nov. 30th) and they estimated her LMP to be 7w3d which would be Oct. 9th. I am confused about these dates for several reasons. First, she said the last period she really had was on September 19th, she is saying that she missed her next period (Oct. 9th?) and ovulated again, and she became pregnant Oct. 21 or 23. Do these dates add up?
Mon, 16 Dec 2013
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OB & GYN Specialist,  's  Response
Hello,

Gestational age or pregnancy period is actually calculated from D1 of her last menstrual period. However, in some cases, late conception may cause 2 to 3 weeks less estimation of gestational period from LMP calculation.

Ultrasound scan gives overall estimation of fetal maturity at that stage and it doesn't always coincide with LMP calculated gestational age. You can consult with your doctor regarding this.
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How Can Exact Conception Dates Be Estimated?

Hello, Gestational age or pregnancy period is actually calculated from D1 of her last menstrual period. However, in some cases, late conception may cause 2 to 3 weeks less estimation of gestational period from LMP calculation. Ultrasound scan gives overall estimation of fetal maturity at that stage and it doesn t always coincide with LMP calculated gestational age. You can consult with your doctor regarding this.