The clear, yellowy fluid that commonly smells like hay and surrounds your baby in utero. It varies in quantity and constitution throughout pregnancy. Initially, it is mainly made up of water and electrolytes changing in the second trimester to contain more dissolved nutrients including fats, carbohydrates, and proteins. As your baby starts to pass urine in utero around 11-16 weeks this also contributes to the fluid. Research has shown that amniotic fluid also contains stem cells that can grow into a variety of different structures including brain, liver, and bone (Fraser, D. & Cooper, M. 2012).