Amniotic fluid

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Amniotic fluid
10-week-old human fetus surrounded by amniotic fluid within the amniotic sac
Identifiers
MeSHD000653
Anatomical terminology
Tubes filled with amniotic fluid for Amniocentesis

The amniotic fluid is the protective liquid contained by the

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).

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

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.

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

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.

Complications related to amniotic fluid

Too little amniotic fluid is 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

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

Main article: Amniotic stem cells

Recent studies show that amniotic fluid contains a considerable quantity of stem cells.

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

References

  1. ^
    ISBN 978-0443065835
    .
  2. ^
    S2CID 1302607
    .
  3. ^
    PMID 15861199
    .
  4. PMID 576129
    .
  5. ^ Forewaters and hindwaters in Q&A section at babyworld.co.uk Archived 2007-10-09 at the Wayback Machine
  6. PMID 25015803
  7. ^ a b 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. S2CID 24731335
    .
  9. PMID 21547164
    .
  10. PMID 23093978
    .
  11. 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. 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. S2CID 6676167
    .
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