Medical Questions > Pregnancy Forum > Pregnancy Calendar Conception : When did I Conceive ? Forum

ultrasound dating

On 2/09/10 I had an ultrasound and the Dr. said that I was 4-4 1/2 weeks pregnant. I obtained the ultrasound report, which did not give a length of pregnancy. There was a yolk sac but no fetal pole. On 3/19/10 I had another ultrasound at the same er. The report from that visit said I was 10 wks 1 day pregnant with a fetal heart rate of 170 bpm. My cycle is irregular (the last period before the one I had in Jan was either at the end of Oct or the start of Nov). On Jan 1st I had a very heavy period lasting until Jan 5th. The ultrasound tech asked my lmp but not my cycle length. If I were to estimate conception based on lmp with a 28 day cycle that would have put it at around jan 15th. If based on the ultrasound, assuming they were estimating gestational age then that would put it around Jan 21st. If the ultrasound was going by fetal age then that would put it around Jan 7th. How would the date most likely be determined at the er? I know that it is from fetal measurements but my report did not contain any. Are they most likely basing this on a 40 week or 38 week pregnancy? One concern is that I drank very heavily until feb 6th, when I had a positive home test. Also.. is it possible that I could have conceived before Jan 1st?
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replied April 3rd, 2010
Especially eHealthy
Preggers, The first scan was too early to date the fetus so they could not give you an age. Only after week 6 can they determine gestational age.

The most common calendar used in the USA is the 40 week one that will have conception on week 2 day 1. Do you have a due date?

A 40 week calendar will put conception on Jan 30. If they use a 38 week calendar, it will be 14 days earlier (Jan 16).

Take care!
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replied April 3rd, 2010
Thank you for the reply, Susan. You are right.
Here is the update: Today it finally struck me to call the hospital and get some answers. Once connected to the ultrasound department they told me that the ultrasound machine is set to a 40 week calendar. Yay! Smile
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