Will my baby get flathead if she keep sleeping on one side?

Yes, your baby will get flathead if sleeping on particular side only. My friend's baby also likes to sleep on his left side only. He needs to go for physical therapy by wearing helmet until he is about 7 months old to correct the head shape. The Flat Head Syndrome is known as Plagiocephaly – this is the most common type and occurs when the head is flattened on one side, causing it to look asymmetrical and distorted. For example, the ears may be misaligned and when seen from above the head, looks like a parallelogram. http://www.nhs.uk/Conditions/plagiocephaly/Pages/Introduction.aspx It's partly due to sleeping position, lying on the back and sleep on one side. However, there are other factors such as factors in the womb, premature births, muscle problems and Craniosynostosis. http://www.nhs.uk/Conditions/plagiocephaly/Pages/Introduction.aspx