when did i conceive?

[leelee51]

Hi, I just need a little help. O.K, my cycle came on around Dec.11-12 2012 somewhere around in there. I took a home pregnancy test before my cycle came on and it came up negative. I had a sonogram done today which says i'm 8 wks and 3 dys. So I was pregnant before my cycle came on?

[AnnieBrooke]

Hi, leelee, yes they do look at embryo size.  In fact, if you walked in and told them an entirely made up first day of your last period, and their ultrasound suggested something else from the baby's size, medical practice is to believe what the ultrasound shows and ignore the woman's self-reported first day of her cycle.  (For women with really irregular cycles, where they might have a period five weeks before they ovulate, this is not such a bad idea.)

Thing is, they have data and charts based on thousands of women whose first day of their last period was a known date, and they note the size of the embryo in relation to that starting point.  This doesn't mean any doctor in the world thinks a woman is pregnant on the first day of her last period.  But it is used as a handy starting point because it is a big obvious signal.  In my mom's day, they didn't have ultrasounds, so the only start point available was the first day of bleeding of the last period the woman had before she got pregnant.  All the books with pictures of fetal development are calibrated to that counting system so they can tie the date to something definite.  All the textbooks for medical students use that counting system.  All doctors and nurses use that language.  Even the pregnant woman uses that language.  (I can remember telling my friend "I'm 11 weeks pregnant," even though I had done my IVF nine weeks earlier.  You get used to it!  lol)

Anyway, you were not pregnant before your cycle came on.

[leelee51]

There not looking at the baby size just from the last cycle period?

[AnnieBrooke]

Are you familiar with where a doctor begins the pregnancy count?  When they tell you a phrase like "You are 8 weeks 3 days pregnant," they mean that many days past the presumed first day of your last period.  They don't mean from conception.  A 'gestational age' count given by a medical person does not start from conception.  (Medical personnel always use the presumed first day of bleeding as day 1 of pregnancy even though they would agree you did not conceive then.)  Therefore, if you were at 8 weeks 3 days pregnant today, you would have conceived around 6 weeks 3 days back from today, or around December 16.  That would be a relatively early ovulation in relation to when you think your period began, but it is not impossible to ovulate early.