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Dr. K.
Dr. K., MD
Category: Medical
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Experience:  Board certified.
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I read somewhere that a fetus can be measured as early as

Customer Question

I read somewhere that a fetus can be measured as early as 5-6 weeks after last mensural period. Is that correct even if ovulation occurs late in the cycle? May be in week 4 after the cycle?
Submitted: 11 months ago.
Category: Medical
Expert:  Dr. K. replied 11 months ago.

A fetus can be seen and measured about 5.5 weeks after the first day of the last menstrual period. This is only if the periods are about 28 days apart, of course. The fetus is then about 3.5 weeks old. If ovulation occurs 4 weeks into the cycle, there would be no fetus to measure that early.

Customer: replied 11 months ago.
I had my LMP on 20th Aug 2015. And had unprotected sex on Oct 1st. On Oct 23rd, the ultrasound measured CRL 1.61cm with GA 8 weeks. So, did the pregnancy occur on Oct 1st? Or I was already pregnant??
Expert:  Dr. K. replied 10 months ago.
The gestational age is always calculated as if the cycle is 28 days. So you conceived around Sept 11. You ovulated about a week late. You did not conceive on Oct 1. It is not at all possible.