What Does Fetus Having Small Stomach Indicate?

Hy.. I am 26 weeks pregnant. I had an altrasound before one month and my doctor told me that my baby has small stomach. I had another altrasaund yesterday and my doctor dold me that stomach is still small (1.56x0.76). all other mesaurement are ok. The problem is just stomach. I am verry worried. What does it mean? How big stomach must be? Will my baby be ok?