Amniotic fluid

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Amniotic fluid
Human fetus 10 weeks with amniotic sac - therapeutic abortion.jpg
10-week-old human fetus surrounded by amniotic fluid within the amniotic sac
Identifiers
MeSH D000653
Anatomical terminology
Tubes filled with amniotic fluid for Amniocentesis Amniocentesis tubes.jpg
Tubes filled with amniotic fluid for Amniocentesis

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.

Contents

For humans, the amniotic fluid is commonly called water or waters (Latin liquor amnii).

Development

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 around week 16, fetal urine also contributes to the fluid. [1] In earlier times, it was believed that the amniotic fluid was composed entirely of excreted fetal urine.

The fluid is absorbed through the fetal tissue and skin. [2] After 22 to 25 week of pregnancy, keratinization of an embryo's skin occurs. When this process completes around the 25th week, [2] the fluid is primarily absorbed by the fetal gut for the remainder of gestation. [1]

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, 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.

Volume

The volume of amniotic fluid changes with the growth of fetus. 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. [3] Approximately in the 10th–11th week, the breathing and swallowing of the fetus slightly decrease the amount of fluid. 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 800 millilitres (28 imp fl oz; 27 US fl oz) by the 28-week gestational age. The amount of fluid declines to roughly 400 millilitres (14 imp fl oz; 14 US fl oz) at 42 weeks. [3] Some sources indicate about 500 to 1,000 millilitres (18 to 35 imp fl oz; 17 to 34 US fl oz) of amniotic fluid is present at birth. [1] [4]

Rupture of membranes

The forewaters are released when the amnion ruptures. This is commonly known as "water breaking". 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 "pre-labour rupture of membranes". Spontaneous rupture of membranes before term 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. [5]

Function

Swallowed amniotic fluid (in later stages of development) creates urine and contributes to the formation of meconium. Amniotic fluid protects the developing fetus 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. It also protects 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 reflex, and functional connectivity of afferent O2 chemoreceptor activity with respiratory motoneurons and arousal centers. [6]

Clinical significance

Collection

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 a low risk procedure, with risk of pregnancy loss between 1 in 1,500 – 1 in 700 procedures. Amniocentesis can be performed to obtain diagnostic genetic information, evaluate for intrauterine infection, or rarely, to assess for fetal lung maturity if early delivery is required. If warranted, fluid is collected between 16 and 42 weeks of fetal development. The amount of fluid removed depends on the indication for the procedure and the testing that will be performed on the fluid.

Analysis

Analysis of amniotic fluid can reveal many aspects of the baby's genetic health as well as the age and viability of the fetus. This is because the fluid contains metabolic wastes and compounds used in assessing fetal age and lung maturity, but amniotic fluid also contains fetal cells, which can be examined for genetic defects.

Amniotic fluid normally has a pH of 7.0 to 7.5. [7] Because pH in the upper vagina is normally acidic (pH 3.8–4.5), a vaginal pH test showing a pH of more than 4.5 strengthens a suspicion of rupture of membranes in case of clear vaginal discharge in pregnancy. [7] Other tests for detecting amniotic fluid mainly include nitrazine paper test and fern test. [8] One main test that is performed on amniotic fluid is the L/S ratio test (lecithin/sphingomyelin). This test is used to determine fetal lung maturity. Both lecithin and sphingomyelin are lung surfactants that are present in increasing amounts in the maturing fetus, though past week 33, sphingomyelin levels remain relatively constant. Measuring a ratio of L/S of 2:1 or greater indicates that the fetus can be safely delivered, with functioning lungs.

Too little amniotic fluid is called oligohydramnios. In a minority of cases it can be a cause of problems for the mother and baby. These include contracture of the limbs, clubbing of the feet and hands, and also a life-threatening condition called hypoplastic lungs. The Potter sequence refers to a constellation of findings related to insufficient amniotic fluid.

On every prenatal visit, the obstetrician, gynaecologist or midwife should measure the patient's fundal height with a tape measure. It is important that the fundal height be measured and properly recorded to track proper fetal growth and the increasing development of amniotic fluid. The obstetrician, gynaecologist or midwife should also routinely ultrasound the patient—this procedure will also give an indication of proper fetal growth and amniotic fluid development. Oligohydramnios can be caused by infection, kidney dysfunction or malformation (since much of the late amniotic fluid volume is urine), procedures such as chorionic villus sampling (CVS), and preterm premature rupture of membranes (PPROM). Oligohydramnios can sometimes be treated with bed rest, oral and intravenous hydration, antibiotics, steroids, and amnioinfusion.[ citation needed ]

The opposite of oligohydramnios is polyhydramnios, an excess volume of amniotic fluid in the amniotic sac.

Amniotic fluid embolism is a rare but very often fatal condition for both mother and child.

Medical applications

It is being used in some surgeries of the outside of the eye. [9] It is also being studied for some orthopaedic conditions. [10] [11]

Stem cell research

Recent studies show that amniotic fluid contains a considerable quantity of stem cells. [12] These amniotic stem cells [13] [14] are pluripotent and able to differentiate into various tissues, which may be useful for future human application. [15] [16] [17] Some researchers have found that amniotic fluid is also a plentiful source of non-embryonic stem cells. [18] These cells have demonstrated the ability to differentiate into a number of different cell-types, including brain, liver and bone.

It is possible to conserve the stem cells extracted from amniotic fluid in private stem cells banks.

See also

Related Research Articles

<span class="mw-page-title-main">Amniocentesis</span> Sampling of amniotic fluid done mainly to detect fetal chromosomal abnormalities

Amniocentesis is a medical procedure used primarily in the prenatal diagnosis of genetic conditions. It has other uses such as in the assessment of infection and fetal lung maturity. Prenatal diagnostic testing, which includes amniocentesis, is necessary to conclusively diagnose the majority of genetic disorders, with amniocentesis being the gold-standard procedure after 15 weeks' gestation.

The amniotic sac, also called the bag of waters or the membranes, is the sac in which the embryo and later fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo until shortly before birth. The inner of these membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the embryo. The outer membrane, the chorion, contains the amnion and is part of the placenta. On the outer side, the amniotic sac is connected to the yolk sac, the allantois, and via the umbilical cord, the placenta.

Fetal distress, also known as non-reassuring fetal status, is a condition during pregnancy or labor in which the fetus shows signs of inadequate oxygenation. Due to its imprecision, the term "fetal distress" has fallen out of use in American obstetrics. The term "non-reassuring fetal status" has largely replaced it. It is characterized by changes in fetal movement, growth, heart rate, and presence of meconium stained fluid.

<span class="mw-page-title-main">Chorionic villus sampling</span> Type of prenatal diagnosis done to determine chromosomal or genetic disorders in the fetus

Chorionic villus sampling (CVS), sometimes called "chorionic villous sampling", is a form of prenatal diagnosis done to determine chromosomal or genetic disorders in the fetus. It entails sampling of the chorionic villus and testing it for chromosomal abnormalities, usually with FISH or PCR. CVS usually takes place at 10–12 weeks' gestation, earlier than amniocentesis or percutaneous umbilical cord blood sampling. It is the preferred technique before 15 weeks.

<span class="mw-page-title-main">Polyhydramnios</span> Excess of amniotic fluid in the amniotic sac

Polyhydramnios is a medical condition describing an excess of amniotic fluid in the amniotic sac. It is seen in about 1% of pregnancies. It is typically diagnosed when the amniotic fluid index (AFI) is greater than 24 cm. There are two clinical varieties of polyhydramnios: chronic polyhydramnios where excess amniotic fluid accumulates gradually, and acute polyhydramnios where excess amniotic fluid collects rapidly.

Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (AFI) measures less than 5 cm or when the single deepest pocket (SDP) of amniotic fluid measures less than 2 cm. Amniotic fluid is necessary to allow for normal fetal movement, lung development, and cushioning from uterine compression. Low amniotic fluid can be attributed to a maternal, fetal, placental or idiopathic cause and can result in poor fetal outcomes including death. The prognosis of the fetus is dependent on the etiology, gestational age at diagnosis, and the severity of the oligohydramnios.

<span class="mw-page-title-main">Twin-to-twin transfusion syndrome</span> Medical condition

Twin-to-twin transfusion syndrome (TTTS), also known as feto-fetal transfusion syndrome (FFTS), twin oligohydramnios-polyhydramnios sequence (TOPS) and stuck twin syndrome, is a complication of monochorionic multiple pregnancies in which there is disproportionate blood supply between the fetuses. This leads to unequal levels of amniotic fluid between each fetus and usually leads to death of the undersupplied twin and, without treatment, usually death or a range of birth defects or disabilities for a surviving twin, such as underdeveloped, damaged or missing limbs, digits or organs, especially cerebral palsy.

Rupture of membranes (ROM) or amniorrhexis is a term used during pregnancy to describe a rupture of the amniotic sac. Normally, it occurs spontaneously at full term either during or at the beginning of labor. Rupture of the membranes is known colloquially as "breaking (one's) water," especially when induced rather than spontaneous, or as one's "water breaking". A premature rupture of membranes (PROM) is a rupture of the amnion that occurs at full term and prior to the onset of labor. In cases of PROM, options include expectant management without intervention, or interventions such as oxytocin or other methods of labor induction, and both are usually accompanied by close monitoring of maternal and fetal health. Preterm premature rupture of membranes (PPROM) is when water breaks both before the onset of labor and before the pregnancy's 37 week gestation. In the United States, more than 120,000 pregnancies per year are affected by a premature rupture of membranes, which is the cause of about one third of preterm deliveries.

Potter sequence is the atypical physical appearance of a baby due to oligohydramnios experienced when in the uterus. It includes clubbed feet, pulmonary hypoplasia and cranial anomalies related to the oligohydramnios. Oligohydramnios is the decrease in amniotic fluid volume sufficient to cause deformations in morphogenesis of the baby.

<span class="mw-page-title-main">Prelabor rupture of membranes</span> Medical condition

Prelabor rupture of membranes (PROM), previously known as premature rupture of membranes, is breakage of the amniotic sac before the onset of labor. Women usually experience a painless gush or a steady leakage of fluid from the vagina. Complications in the baby may include premature birth, cord compression, and infection. Complications in the mother may include placental abruption and postpartum endometritis.

<span class="mw-page-title-main">Chorioamnionitis</span> Medical condition

Chorioamnionitis, also known as intra-amniotic infection (IAI), is inflammation of the fetal membranes, usually due to bacterial infection. In 2015, a National Institute of Child Health and Human Development Workshop expert panel recommended use of the term "triple I" to address the heterogeneity of this disorder. The term triple I refers to intrauterine infection or inflammation or both and is defined by strict diagnostic criteria, but this terminology has not been commonly adopted although the criteria are used.

Postterm pregnancy is when a woman has not yet delivered her baby after 42 weeks of gestation, two weeks beyond the typical 40-week duration of pregnancy. Postmature births carry risks for both the mother and the baby, including fetal malnutrition, meconium aspiration syndrome, and stillbirths. After the 42nd week of gestation, the placenta, which supplies the baby with nutrients and oxygen from the mother, starts aging and will eventually fail. Postterm pregnancy is a reason to induce labor.

<span class="mw-page-title-main">Nuchal scan</span> Routine ultrasound done between 11 and 14 weeks pregnancy

A nuchal scan or nuchal translucency (NT) scan/procedure is a sonographic prenatal screening scan (ultrasound) to detect chromosomal abnormalities in a fetus, though altered extracellular matrix composition and limited lymphatic drainage can also be detected.

Amniotic fluid index (AFI) is a quantitative estimate of amniotic fluid and an indicator of fetal well-being. It is a separate measurement from the biophysical profile.

<span class="mw-page-title-main">Velamentous cord insertion</span> Velamentous placenta

Velamentous cord insertion is a complication of pregnancy where the umbilical cord is inserted in the fetal membranes. It is a major cause of antepartum hemorrhage that leads to loss of fetal blood and associated with high perinatal mortality. In normal pregnancies, the umbilical cord inserts into the middle of the placental mass and is completely encased by the amniotic sac. The vessels are hence normally protected by Wharton's jelly, which prevents rupture during pregnancy and labor. In velamentous cord insertion, the vessels of the umbilical cord are improperly inserted in the chorioamniotic membrane, and hence the vessels traverse between the amnion and the chorion towards the placenta. Without Wharton's jelly protecting the vessels, the exposed vessels are susceptible to compression and rupture.

<span class="mw-page-title-main">Lecithin–sphingomyelin ratio</span> Test of fetal amniotic fluid to assess for lung immaturity

The lecithin–sphingomyelin ratio is a test of fetal amniotic fluid to assess for fetal lung immaturity. Lungs require surfactant, a soap-like substance, to lower the surface tension of the fluid coating the alveolar epithelium in the lungs. This is especially important for premature babies trying to expand their lungs after birth. Surfactant is a mixture of lipids, proteins, and glycoproteins, lecithin and sphingomyelin being two of them. Lecithin makes the surfactant mixture more effective.

Amniotic stem cells are the mixture of stem cells that can be obtained from the amniotic fluid as well as the amniotic membrane. They can develop into various tissue types including skin, cartilage, cardiac tissue, nerves, muscle, and bone. The cells also have potential medical applications, especially in organ regeneration.

<span class="mw-page-title-main">Fetal membranes</span> Amnion and chorion which surround and protect a developing fetus

The fetal membranes are the four extraembryonic membranes, associated with the developing embryo, and fetus in humans and other mammals. They are the amnion, chorion, allantois, and yolk sac. The amnion and the chorion are the chorioamniotic membranes that make up the amniotic sac which surrounds and protects the embryo. The fetal membranes are four of six accessory organs developed by the conceptus that are not part of the embryo itself, the other two are the placenta, and the umbilical cord.

<span class="mw-page-title-main">Circumvallate placenta</span> Medical condition

Circumvallate placenta is a rare condition affecting about 1-2% of pregnancies, in which the amnion and chorion fetal membranes essentially "double back" on the fetal side around the edges of the placenta. After delivery, a circumvallate placenta has a thick ring of membranes on its fetal surface. Circumvallate placenta is a placental morphological abnormality associated with increased fetal morbidity and mortality due to the restricted availability of nutrients and oxygen to the developing fetus.

Amnioinfusion is a method in which isotonic fluid is instilled into the uterine cavity.

References

  1. 1 2 3 Larsen, William J. (2001). Human embryology (3. ed.). Philadelphia, Pa.: Churchill Livingstone. p. 490. ISBN   978-0443065835.
  2. 1 2 Underwood, Mark A.; Gilbert, William M.; Sherman, Michael P. (May 2005). "Amniotic Fluid: Not Just Fetal Urine Anymore - Journal of Perinatology". Journal of Perinatology. 25 (5): 341–348. doi: 10.1038/sj.jp.7211290 . PMID   15861199. S2CID   1302607.
  3. 1 2 Underwood, Mark A; Gilbert, William M; Sherman, Michael P (24 March 2005). "Amniotic Fluid: Not Just Fetal Urine Anymore". Journal of Perinatology. 25 (5): 341–348. doi: 10.1038/sj.jp.7211290 . PMID   15861199.
  4. ↑ Caroline, Nancy L. (1977-01-03). "Medical Care in the Streets". JAMA: The Journal of the American Medical Association. 237 (1): 43–6. doi:10.1001/jama.1977.03270280045020. ISSN   0098-7484. PMID   576129.
  5. ↑ Forewaters and hindwaters in Q&A section at babyworld.co.uk Archived 2007-10-09 at the Wayback Machine
  6. ↑ Koos, Brian J.; Rajaee, Arezoo (2014), "Fetal Breathing Movements and Changes at Birth", Advances in Fetal and Neonatal Physiology, vol. 814, Springer New York, pp. 89–101, doi:10.1007/978-1-4939-1031-1_8, ISBN   9781493910304, PMID   25015803
  7. 1 2 Vaginal pH Test Archived 2014-06-01 at the Wayback Machine from Point of Care Testing, July 2009, at: University of California, San Francisco – Department of Laboratory Medicine. Prepared by: Patricia Nassos, PhD, MT and Clayton Hooper, RN.
  8. ↑ Bennett, S.; Cullen, J.; Sherer, D.; Woods Jr, J. (2008). "The Ferning and Nitrazine Tests of Amniotic Fluid Between 12 and 41 Weeks Gestation". American Journal of Perinatology. 10 (2): 101–104. doi:10.1055/s-2007-994637. PMID   8476469. S2CID   24731335.
  9. ↑ Meller, Daniel; Pauklin, Mikk; Thomasen, Henning; Westekemper, Henrike; Steuhl, Klaus-Peter (2011). "Amniotic Membrane Transplantation in the Human Eye". Deutsches Ärzteblatt International. 108 (14): 243–248. doi:10.3238/arztebl.2011.0243. ISSN   1866-0452. PMC   3087122 . PMID   21547164.
  10. ↑ Rennie, Kerry; Gruslin, Andrée; Hengstschläger, Markus; Pei, Duanqing; Cai, Jinglei; Nikaido, Toshio; Bani-Yaghoub, Mahmud (2012). "Applications of Amniotic Membrane and Fluid in Stem Cell Biology and Regenerative Medicine". Stem Cells International. 2012: 721538. doi: 10.1155/2012/721538 . ISSN   1687-966X. PMC   3474290 . PMID   23093978.
  11. ↑ Frank, Rachel M.; Cole, Brian J. (2018-11-22). OrthoBiologics in Sports Medicine , An Issue of Clinics in Sports Medicine, E-book. Elsevier Health Sciences. ISBN   978-0-323-65495-1.
  12. ↑ "Stem cells in amniotic fluid show promise", Los Angeles Times, Jan 8 2007, retrieved 27 July 2009
  13. ↑ De Coppi, Paolo; Bartsch, Georg; Siddiqui, M Minhaj; Xu, Tao; Santos, Cesar C.; Perin, Laura; Mostoslavsky, Gustavo; Serre, Angéline C.; Snyder, Evan Y.; Yoo, James J.; Furth, Mark E.; Soker, Shay; Atala, Anthony (2007). "Isolation of amniotic stem cell lines with potential for therapy". Nature Biotechnology. 25 (1): 100–106. doi:10.1038/nbt1274. PMID   17206138. S2CID   6676167.
  14. ↑ "Scientists See Potential In Amniotic Stem Cells", Washington Post, Jan 8 2007, retrieved 27 July 2009
  15. ↑ "Amniotic Fluid Yields New Type of Stem Cell" Archived 2014-01-22 at the Wayback Machine , PBS - The Online News Hour, Jan 8 2007, retrieved 27 July 2009
  16. ↑ "Versatile Stem Cell Identified in Amniotic Fluid", Pamela J. Hines, International Society of Stem Cell Research, March 21, 2008, retrieve 27 July 2009 "ISSCR :: Public : Stem Cell Briefings". Archived from the original on 2009-04-06. Retrieved 2009-05-09.
  17. ↑ "Amniotic Stem Cells - "Mesenchimal Stem Cells in Human Application", Biocell Center Group, 2009, retrieved 27 July 2009 "Archived copy" (PDF). Archived from the original (PDF) on 2009-04-19. Retrieved 2009-05-09.{{cite web}}: CS1 maint: archived copy as title (link)
  18. ↑ De Coppi, Paolo; Bartsch, Georg; Siddiqui, M Minhaj; Xu, Tao; Santos, Cesar C.; Perin, Laura; Mostoslavsky, Gustavo; Serre, Angéline C.; Snyder, Evan Y.; Yoo, James J.; Furth, Mark E.; Soker, Shay; Atala, Anthony (2007). "Isolation of amniotic stem cell lines with potential for therapy". Nature Biotechnology. 25 (1): 100–106. doi:10.1038/nbt1274. PMID   17206138. S2CID   6676167.
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