Is There A Risk In Taking NT Scan At 12 Weeks Of Pregnancy?

Posted on Sun, 24 Nov 2013

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

Sun, 24 Nov 2013 Answered on

Mon, 16 Dec 2013 Last reviewed on

Question : Hi, My wife is 12 weeks into her second pregnancy, the early scan was good (143 bpm at 7 wk 3 days and CRL matched her gestational age) and I took her for NT scan on 23/11/13. The sonologist identified that the baby is curled up and asked us to come back after our lunch, on returning back from lunch the baby appeared in the right position and she took the CRL ( which measured as 59mm, correct to gestational age) and almost in no time said the baby is too small for a NT scan and advised us to come back in a week's time. I dont know what was running in the Sonographer's mind if there is something abnormal that forced her to tell us to come back after a week. Am certain though that the scan lasted only 10 seconds at best where she took just the CRL and said it is best to give a week cos the baby is too small now. I dont have any further information to add but just wanted to know even though NT scan range is 11-13 wk 6 as I understood from the net, will it be possible for the Sonographers to take a different stand and push the scan dates for a better scan ? note in a week's time my wife will still be comfortably under 13 wk 6 day. Again you may not be able to tell why we were turned down and asked to come back in a week , any help however will be greatly apperciated. I would have thought that if there was a genuine risk she would have highlighted at the earliest opportunity rather than delaying the scan by a week further. What baffles me is that given the CRL correct to GA and virtually every article I read about NT scan indicates no problem in taking an NT scan at 12 weeks, why we were asked to wait for a week further for an NT scan.

Answered by Dr. Aarti Abraham (57 minutes later)

Brief Answer: NO REASON LOGICALLY TO DEFER SCAN. Detailed Answer: Hello XXXXX Thanks for writing to us with your health concern. The NT scan is ideally best done between 11 - 14 weeks gestation. Studies indicate that the test results are most accurate when done at 12 weeks or 13 weeks. If the CRL and GA correspond to 12 weeks, I can see no reason why she would have deferred the scan. Rest assured that if there was a genuine risk / abnormal result observed, then she would have definitely notified you, and reported the scan. All I can guess is that she was busy, and hence deferred the scan ! Studies in fact show that 12 weeks is a slightly better time to measure the NT, rather than 13 weeks. However, you can only know the reality once she repeats the scan in a week's time, and that too would be optimum, because she would still be under 14 weeks then. As you have rightly stated, it is very difficult to tell you why you were asked to return after a week ( other than getting into the sonographer's mind and reading her thoughts ! ) . It would have been better to ask her itself why she was delaying the scan. It is possible, that the baby corrected itself, but once she again started scanning, the position was not found to be proper ( babies can turn and move every second ) - that is another possibility I can think of. Also, was it a transvaginal scan - if it was an abdominal scan, she might have felt that the patient's bladder was full, and then the NT measurement becomes difficult. These are just a few guesses - 12 weeks was good enough to have an NT scan, why it was not done, can only be answered by her ! Do not worry in any case, as next week too you would be within range to have a scan. All the best. Please feel free to ask for further clarifications.

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