Hello ma'am, the nuchal fold thickness is what we refer to as a 'Soft marker' in medical jargon. It's significance reduces after 12 week ultrasound and by 20 weeks the likelihood of this being interpreted as a concerning feature further drops if all other parameters are normal. I would advice you to not worry about it and take care of yourself without undue stress. Kindly note that all the ultrasound findings are observer based which are largely dependent on the position of the child.
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Eat well. Rest well. Stay happy. Tender love and care is prescribed by your doctor😊