Amniotic fluid

The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. 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. The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. 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. For humans, the amniotic fluid is commonly called water or waters (Latin liquor amnii). Amniotic fluid is present from the formation of the gestational sac. Amniotic fluid is 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. In earlier times, it was believed that the amniotic fluid was composed entirely of fetal urine. The fluid is absorbed through the fetal tissue and skin. After the 15th-25th week of pregnancy when the keratinization of an embryo's skin occurs, the fluid is primarily absorbed by the fetal gut. 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. 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-11th 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 500 cc to1L of amniotic fluid at birth. The forewaters are released when the amnion ruptures. This is commonly known as the time when a woman's 'water breaks'. When this occurs during labour at term, it is known as 'spontaneous rupture of membranes'. If the rupture precedes labour at term, however, it is referred to as 'premature rupture of membranes'. The majority of the hindwaters remain inside the womb until the baby is born. Artificial rupture of membrane (ARM), a manual rupture of the amniotic sac, can also be performed to release the fluid if the amnion has not spontaneously ruptured. Swallowed amniotic fluid (in later stages of development) creates urine and contributes to the formation of meconium. Amniotic fluid protects the developing baby by cushioning against blows to the mother's abdomen, allowing for easier fetal movement and promoting muscular/skeletal development. Amniotic fluid swallowed by the fetus helps in the formation of the gastrointestinal tract. Contrary to popular belief, amniotic fluid has not been conclusively shown to be inhaled and exhaled by the fetus. In fact, studies from the 1970s show that in a healthy fetus, there is no inward flow of amniotic fluid into the airway. Instead, lung development occurs as a result of the production of fetal lung fluid which expands the lungs. It also prevents the fetus from mechanical jerks and shocks. The fetus, which develops within a fluid-filled amniotic sac, relies on the placenta for respiratory gas exchange rather than the lungs. While not involved in fetal oxygenation, fetal breathing movements (FBM) nevertheless have an important role in lung growth and in development of respiratory muscles and neural regulation. FBM are regulated differently in many respects than postnatal respiration, which results from the unique intrauterine environment....At birth, the transition to continuous postnatal respiration involves a fall in temperature, gaseous distention of the lungs, activation of the Hering-Breuer reflexes, and functional connectivity of afferent O2 chemoreceptor activity with respiratory motoneurons and arousal centers. Amniotic fluid is removed from the mother by an amniocentesis procedure, where a long needle is inserted through the abdomen into the amniotic sac, using ultrasound guidance such that the fetus is not harmed. Amniocentesis is an abnormal procedure, and is only performed if there is a suspicion of health defects in the fetus, or if an early delivery of the fetus may be necessary, since there can be complications from the procedure. If warranted, fluid is collected between 16–42 weeks of fetal development, and 20-30ml of fluid are removed.