Di/Di Growth at 31 Weeks

Hi all,

FTM here, 31 weeks with Di/Di BG twins and just came from my growth scan - Twin A Girl has always been a bit behind Twin B Boy in weight/size. He has consistently been measuring big throughout the pregnancy. However, today the tech mentioned she is 3lb11oz and in the 18th percentile while he is 4lb11oz 84th percentile. Her growth has actually gone DOWN since my last growth scan and I am freaking out. She didn't seem overly concerned and said its normal for twins to be different sizes and if they were singletons they are exactly where they should be. She is having me make an appointment with a MFM next week and again, while she didn't seem overly concerned I am a mess. Why would her growth be going down? Everything I have looked up sounds scary - has anyone else dealt with this? What was the outcome?

Any feedback is greatly appreciated, thank you!