How do doctors find out a baby's gender/sex when it is in the uterus?

How long on average, does it take for a foetus to develop in the human uterus?

What develops first in a human embryo? 

At what week does the heart of the embryo start beating?

At what age might a baby start to smile?

Amphibians are invertebrates.

What do we call a young bird as it grows and develops ready to leave the nest? 

What does the word incubate mean?

What develops to allow a tadpole to leave the water? 

What is a dragonfly larva called?