Amniotic fluid

The amniotic fluid, commonly called a pregnant woman's water or waters (Latin liquor amnii), is the protective liquid contained by the amniotic sac of a pregnant female.

Development

Amniotic fluid is present from the formation of the gestational sac. Amniotic fluid is present in the amniotic sac. It is generated from maternal plasma, and passes through the fetal membranes by osmotic and hydrostatic forces. When fetal kidneys begin to function in about week 16, fetal urine also contributes to the fluid.

The fluid is absorbed through the fetal tissue and skin. After the 20th-25th week of pregnancy when the keratinization of an embryo's skin occurs, the fluid is primarily absorbed by the fetal gut.

Contents

At first, amniotic fluid is mainly water with electrolytes, but by about the 12-14th week the liquid also contains proteins, carbohydrates, lipids and phospholipids, and urea, all of which aid in the growth of the fetus.

Volume

The volume of amniotic fluid increases with the growth of fetus. From the 10th to the 20th week it increases from 25ml to 400ml approximately. Approximately in the 10th week the breathing and swallowing of the fetus slightly decrease the amount of fluid, but neither urination nor swallowing contributes significantly to fluid quantity changes, until the 25th week, when keratinization of skin is complete. Then the relationship between fluid and fetal growth stops. It reaches a plateau of 800ml by the 28 week gestational age. The amount of fluid declines to roughly 400 ml at 42 weeks. There is about 1L of amniotic fluid at birth.