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What causes differences in the gestational age from ultrasound scan and the last period date?

DOCTOR OF THE MONTH - Apr 2014
Apr 2014
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Answered by

Radiologist
Practicing since : 2004
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Question
Hi I'm writing down the results of the second scan that I had and some other information regarding my pregnancy period.

2nd scan report
-------------------------
Mean sac dia: 6mm
Mean yolk size: 2.5mm

The first scan (tas) was done on the 14th of July and a thickened endometrium of 21mm was detected.

The second scan (tvs) was carried out on 25th July. The last menstrual period was on the 14th of XXXXXXX and I had slight bleeding (dark brown color) on the 11th, 12th and 15th July.

Also, the gestational age from the scan reveals a time period of less than 5 weeks. And, the last menstrual period 5.5 weeks.

Why is there a difference in the gestational age from the scan and the last period date? Also what are the chances of miscarriage? What should I be doing at this time and do you have any advices for me?

Please answer all the questions above. Hope to hear soon! Thanks!
Posted Sat, 16 Aug 2014 in X-ray, Lab tests and Scans
 
 
Answered by Dr. Indu Kumar 54 minutes later
Brief Answer:
Calculation by LMP is more accurate in early weeks

Detailed Answer:
Hello XXXXXXX
Thanks for writing to HCM

Gestational age by your LMP is more accurate as compared to Ultrasound if you have regular periods.You can rely on LMP calculation.
There may be some technical error in measurement during ultrasound.This matters a lot in early gestational age.Embryo is very small in early weeks and even mm difference in measurement may alter the results.

You don't worry at all.LMP calculation is more accurate in early weeks.
With advancement of pregnancy,ultrasound will give more accurate maturity results.

Fetal pole is not commented in your report.If fetal pole is not seen in present scan then repeat scan can be done after 2 weeks.
If fetal pole is still not seen in follow up scan then missed abortion can be concluded.

At present you should take proper rest and hope for the best.
It is too early to comment about abortion.

Wish you all the best.
Hope I have answered your question.
Further queries are most welcome.

Take Care
Dr.Indu XXXXXXX
Above answer was peer-reviewed by
 
Follow-up: What causes differences in the gestational age from ultrasound scan and the last period date? 3 hours later
Thanks for replying..

I wanted to know if the sac and yolk sizes are normal.. also a fetal pole was not seen..
 
 
Answered by Dr. Indu Kumar 18 hours later
Brief Answer:
Please find detail answer below.

Detailed Answer:
Hello XXXXXXX
Thanks for writing back

Yes,sizes are fine,but more important is contour of G-sac means whether is regular in shape or not.
You need follow up scan as fetal pole is not seen in present scan.

Wish you all the best.
Hope I have answered your question.
Further queries are most welcome.

Take Care
Dr.Indu XXXXXXX
Above answer was peer-reviewed by
 
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