Sometimes, they just can not see. My friend was told at her NT scan that the us tech was 75% sure it was a girl and it was.
At our NT scan, the us tech asked DP and I if we were going to find out the sex, we are (hopefully) so she had a look around but just couldn't get on the right angle to see.
DP's good friends went in at 20 weeks and bub just wouldn't cooperate, so they had a surprise.
I think you should just be happy you are having a baby and got to see it again, gender or no.
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