Approximately in the 10th–11th week, the breathing and swallowing of the fetus slightly decrease the amount of fluid. From the 10th to the 20th week it increases from 25 to 400 millilitres (0.88 to 14.08 imp fl oz 0.85 to 13.53 US fl oz) approximately. The volume of amniotic fluid changes with the growth of fetus. Contents Īt first, amniotic fluid is mainly water with electrolytes, but by about the 12–14th week the liquid also contains proteins, carbohydrates, lipids and phospholipids, urea, and extracellular matrix ECM components including collagens and glycosaminoglycans, including hyaluronic acid and chondroitin sulfate, all of which aid in the growth of the fetus. When this process completes around the 25th week, the fluid is primarily absorbed by the fetal gut for the remainder of gestation. After 22 to 25 week of pregnancy, keratinization of an embryo's skin occurs. The fluid is absorbed through the fetal tissue and skin. In earlier times, it was believed that the amniotic fluid was composed entirely of excreted fetal urine. When fetal kidneys begin to function around week 16, fetal urine also contributes to the fluid. It is generated from maternal plasma, and passes through the fetal membranes by osmotic and hydrostatic forces. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products between mother and fetus.įor humans, the amniotic fluid is commonly called water or waters (Latin liquor amnii).Īmniotic fluid is present from the formation of the gestational sac. The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote.
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