![]() 64 Morin and Lim performed a literature review with the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada and suggest that the SDP should be used in each sac with standard definitions for singleton pregnancies, although they state that there is not enough evidence to suggest that one method is more predictive than the others of adverse pregnancy outcome. This approach appears reasonable because in the only evaluation of volume in third-trimester diamniotic twin pregnancies, the amniotic fluid volume, or each sac, was similar to that of normal singleton pregnancies. When evaluating the health of the amniotic fluid in twin pregnancies, singleton growth curves currently provide the best predictors of adverse outcomes, and the evaluation of fluid with singleton nomograms is frequently being used. Multifetal pregnancies are at a higher risk of perinatal morbidity and mortality than singleton pregnancies. Martin MBBS, FRACP, in Fanaroff and Martin's Neonatal-Perinatal Medicine, 2020 Twins and Amniotic Fluid 1 An abundance of growth factors are found in amniotic fluid, including epidermal growth factor, transforming growth factor-alpha, transforming growth factor-beta 1, insulin-like growth factor-1, erythropoietin, and granulocyte colony-stimulating factor many of these growth factors play an important role in fetal intestinal development. 5 A variety of carbohydrates, proteins, lipids, electrolytes, enzymes, and hormones, which vary in concentration depending on the gestational age, are also present some of these elements, particularly the amino acids taurine, glutamine, and arginine, serve a nutritive function for mitotic cells involved in trophoblastic growth and placental angiogenesis. By term, the osmolality of amniotic fluid is about 85% to 90% that of maternal serum. The impact of this process, coupled with the ability of the fetal kidneys to produce urine, results in increased amniotic fluid concentrations of urea and creatinine, decreased concentrations of sodium and chloride, and reduced osmolality. Keratinization of the fetal skin is complete by 25 weeks’ gestation and decreases the permeability of fetal tissues to water and solutes. 5 During the first trimester, amniotic fluid consists mostly of water and electrolytes and contains minimal protein. The composition of amniotic fluid undergoes more marked variation than its volume. ![]() Amniotic fluid volume plateaus at 800 mL at around 28 weeks’ gestation, after which it declines to approximately 400 mL at term. 4 Finally, the status of maternal hydration and the amount of decidual prolactin may alter the transfer of amniotic fluid through fetal and maternal tissues. 3 Amniotic fluid volume is also influenced by intramembranous (between amniotic fluid and fetal blood within the placenta) and transmembranous (between amniotic fluid and maternal blood within the uterus) pathways in both physiologic and pathophysiologic states. ![]() After this period, the volume of amniotic fluid is a function of production, from fetal urine (600 to 1200 mL/day near term) and respiratory tract secretions (60 to 100 mL/kg fetal body weight/day), and removal through fetal swallowing (200 to 250 mL/kg fetal body weight/day). During this period, the composition of amniotic fluid is similar to fetal extracellular fluid, owing to the absence of keratin in the fetal skin. 2 Between 10 and 20 weeks’ gestation, the volume of amniotic fluid increases in a predictable and linear manner from approximately 25 mL to 400 mL. The expression of aquaporins changes as gestation advances and with certain pathologic states, such as polyhydramnios. 1 The formation and maintenance of amniotic fluid is an intricate process that depends on fetal maturation and maternal hydration, hormonal status, and uteroplacental perfusion.Īmniotic fluid during early embryogenesis is principally derived from maternal plasma by the passage of water and solutes through aquaporin water channels expressed in the fetal maternal membranes (amnion and chorion). Amniotic fluid serves a number of vital roles, including the facilitation of fetal growth, the provision of a microgravity environment that cushions the fetus, and the generation of a defense mechanism against invading microbes. The fetus is surrounded by amniotic fluid, a complex fluid that changes as the pregnancy progresses. Chestnut MD, in Chestnut's Obstetric Anesthesia, 2020 Amniotic Fluid
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