It's not considered a possible issue unless you are measuring 2 weeks or more off. Babies grow at much different rates once you get further along and grow in spurts. Unless the baby is even further off at your next visit it's perfectly fine.
Hi there... I was measuring 2 weeks behind, was 28 weeks and only measured 26 weeks... but next time I saw my midwife I am bang on where I should be... can be how baby's lying.. they will monitor you and Co tinge to check that you are growing to be safe.. as long as there is growth I don't think you need to stress.. every baby and pregnancy is different