Can an Ultrasound be wrong on a baby's age?

Lynn - posted on 01/29/2015 ( 7 moms have responded )

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I just found out I'm pregnant; because of my age and possible a problem, I have had 3 ultrasounds in 3 weeks. The first ultrasound (2 weeks ago) said I'm 5 weeks 5 days along. The second said I'm 6 weeks 5 days along. Today the doctor said I'm 7 weeks along.
Here is the problem... I have not had sex since the middle/end of November, which would means I should be 10 weeks along. I've expressed my confusion, but the doctor looks at me funny and just says the ultrasound is correct.
Any ideas on what could be going on here? I'm 40, but come on! I know when I have and have not had sex.

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Dove - posted on 01/29/2015

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Ultrasound 'guesses' the age of the baby based on size... so if baby is growing a bit slower (or faster) than their 'average'... yes, the age on the ultrasound could very well be slightly different than baby's actual age.

Sarah - posted on 01/29/2015

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Yes. Ultrasounds are just estimates. There is always a plus or minus of so many days depending on when they do the ultrasound. I am preg. with a calculated due date of May 22. I had an ultrasound at 12 weeks and that put me at May 11 for due date. Then I had another at my original 22 wk. and that put me back at May 22. I had a friend that was pregnant with twins and had multiple ultrasounds each ultrasound gave a different due date. A few things to also remember is not always do you get pregnant the day you have sex. Sperms can live up to 96 hours after sex so you can get pregnant at anytime after you have sex for that time period. Your ovulation could have been off too. In the end baby will come when baby is ready no matter what date they put you at.

Trisha - posted on 01/29/2015

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If you had sex at the VERY end of Nov, you will be at 8.5 weeks. It is possible that the egg wasn't actually fertilized for about 5 days afterwards.

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Trisha - posted on 01/29/2015

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That is strange. Because usually the dating of a fetus is done based on the last date of the last period, which would make it even longer away yet.

Lynn - posted on 01/29/2015

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The last cycle I am certain of was Nov 8th (start)-Nov 13th (end). I'm pretty sure it was about 1.5 weeks after that when I had sex. My next period should have been the week of Dec. 8th, but I didn't log one in my calendar - either because I did not have one or because I don't remember (I had foot surgery that same week). It seems to me that I may have had a very short one that week... or appeared to be starting, and then didn't. Since I was on pain meds from surgery, I don't recall needing to use pain meds for cramps that month, which is why I cannot recall.

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