Suggest Treatment For Disproportion In Fetus' Head And Body

I have had 3 ultrasounds already to measure my baby, in which they were unable to get an accurate head measurement adn stating its much smaller than what it should be due to how far along I am and the size of the rest of his body. I received a vm today from the dr stating "nothing special but we need a second opinion on your baby's head" what could this mean?