Baby has 1 cm difference in leg width?

I took my daughter for her 4 month checkup today, and mentioned that my husband noticed a difference in the size of her legs. The doctor measured her thighs and her right thigh is 1cm bigger than her left. She is sending her for a 2nd opinion and I'm so worried! Does anyone know what this could be? Should I be worried? Anyone else have the same issue with their kids? The lengths are the same and it's only in her legs, no other body parts. The doctor said she just wants a 2nd opinion before she sends my daughter for more tests and not to worry, but how can I not? I have no idea what this could be and it's freaking me out...