Is The Discrepancy In Fetal Age A Cause For Concern?

Posted on Thu, 6 Feb 2014

Medically reviewed by Ask A Doctor - 24x7 Medical Review Team

Thu, 6 Feb 2014 Answered on

Fri, 28 Feb 2014 Last reviewed on

Question : The first day of my last period was October 21, 2013, but in my ultrasound on February 3, the baby measured 9 weeks, 6 days with a due date of September 2. A previous ultrasound on January 23 had shown the baby to be 8 weeks so the baby had grown 2 weeks worth. Is the discrepancy cause for concern? I do have very irregular cycles.

Answered by Dr. Mahesh Koregol (20 minutes later)

Brief Answer: No Detailed Answer: Hi I read your query and I understand your concerns. Following is my reply 1. Congratulations for your pregnancy. 2. The ultrasound always has a margin of error. It has nothing to do with your cycle regularity. 3. First trimester ultrasound has a margin of error by one week plus or minus. 4. When you near second trimester the margin of error is plus or minus 2 weeks. 5. For consideration of dating always consider first scan only as it is most accurate for dating. 6. Hence in your case for dates of expected delivery and duration of pregnancy has to be calculated based in first scan report only. 7. Second scan and scans done after this are for fetal well being and not for dating. Let me know if you have any more questions. Regards Dr. Mahesh Koregol

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar