Ultrasound accuracy for a due date


Q: Please don't publish this question.

My wife had an ultrasound that placed her at 9 weeks 2 days pregnant (conception date around June 13th) . The problem with that ultrasound is that I was not with my wife 9 weeks and 2 days ago. I did not see her until 7 weeks and 5 days ago (June 24th). We had unprotected sex on the day we were together and every day there after for a week or so.

Is there any chance that the ultrasound can be off by that much(10-11 days)? She had a very unusual two cycles before the month she got pregnant.

In May she was 8 days late and then bled heavily from June 1st to June 15th with continued off and on bleeding until the 20th. A doctor put her on birth control pills on the 15th which she took until the 19th and then quit because of headaches.

Yesterday was expected to be a happy day, but the timing of the ultrasound has me freaking and my wife accusing me of not trusting her. I completely trust her, but I can't help but wonder due to the science of the ultra sound.

Symptoms:  Pregnancy

A:   Hello,
Thanks for the query.

Most of the times an ultrasound is accurate in predicting the expected gestational age of the fetus. However, an ultrasound cannot be hundred percent accurate. A lag of one week or advancement of gestational age prediction by one week on an ultrasound is acceptable and it also depends on the efficiency of the person performing an ultrasound. There can be errors in measuring the CRL OR crown lump length which can alter the gestational age and hence give a false conception date.

This can be quite possible in your case. Considering the irregularity in the menstrual cycle and an inaccurate last menstrual period, the ultrasound can just be an estimated predictor.
We suggest that you do not doubt your partner and go in for a second scan from another radiologist or a centre. For now do not worry and relax. Enjoy the new preparatory phase of your parenthood.

In case you still have doubts, you can opt for DNA karyotyping to determine the genetics and predict the parents of the child. However, this would be risky, cumbersome and expensive.

Hope this helped.
Feel free to contact us for further clarification.

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