How do you know if your baby will have a head full of hair at birth andcan you tell by ultrasound pucs?

Interesting question: You can tell on ultrasound if there is hair on the baby's head. However the quality and the quantity of the baby's hair is not well known until the baby is born and grown. You can better guess by looking at the parents. Genetics are the best determinants of the child's features.

Can't tell: Ultrasounds don't show hair growth. Hair in utero is wet with amniotic fluid. When the baby "crowns" at delivery the hair is the first thing you see, so the obstetrician oftens says "lots of hair!" even before the baby is delivered.

Hair ==>Cute images: Let me start with this: looking for hair is not a reason to do or prolong an ultrasound. However, as someone who has done countless ultrasound studies, I have seen fetuses with hair on their heads floating in the fluid. We can sometimes estimate whether there is a full head or only ring-like "monk hair" toward the end of pregnancy. The fetal pictures are cute, but the newborn ones are even cuter!