Embryology, Amniotic Fluid


Article Author:
Emily Fitzsimmons


Article Editor:
Tushar Bajaj


Editors In Chief:
Chaddie Doerr


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Trevor Nezwek
Radia Jamil
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes


Updated:
5/6/2019 10:13:33 AM

Introduction

Amniotic fluid surrounds the embryo and fetus during development and has a myriad of functions.  Physically, it protects the fetus in the event the maternal abdomen is the object of trauma. Furthermore, it protects the umbilical cord by providing a cushion between the fetus and the umbilical cord thus reducing risk of compression between the fetus and the uterine wall.[1]  Amniotic fluid also helps protect the fetus from infectious agents, due to its inherent antibacterial properties.  Additionally, it serves as a reservoir of fluid and nutrients for the fetus containing: proteins, electrolytes, immunoglobulins, and vitamins from the mother.  It provides the necessary fluid, space, and growth factors to allow normal development and growth of fetal organs such as the musculoskeletal system, gastrointestinal system, and the pulmonary system.[2]  Clinicians can use the amniotic fluid as a tool to monitor the progression of pregnancy and predict fetal outcomes.

Development

The development of amniotic fluid organizes into early gestation and late gestation.  Early gestation is the embryonic period which is from the start of fertilization to 8 weeks, and late gestation which encompasses the fetal period 8 weeks to birth.  The composition of amniotic fluid changes from early gestation to late gestation. During the embryonic period, amniotic fluid derives from both fetal and maternal factors such as water from maternal serum, coelomic fluid, and fluid from the amniotic cavity; however, during late gestation, amniotic fluid is largely produced by fetal urine and lung secretions.[3][4]

Early Gestation

In early gestation, two fluid-filled sacs surround the embryo: the exocoelomic cavity and amniotic cavity. The formation of the coelomic cavity begins during the fourth week of gestation when the exocoelomic cavity splits the extraembryonic mesoderm into the splanchnic mesoderm lining and the somatic mesoderm. The coelomic fluid within the coelomic cavity stays in direct contact with the mesenchyme of the developing placenta villi during the first trimester. Before it disappears, the coelomic cavity acts as a transfer area as well as a reservoir of nutrients for the growing embryo. The exocoelomic cavity forms inside the extraembryonic mesoderm alongside the placental chorionic plate and is now believed to be an essential transfer interface and reservoir of nutrients for the embryo because coelomic fluid has shown to have ultrafiltrate of maternal serum as well as products derived from the placenta and secondary yolk sac. This arrangement suggests that the coelomic fluid is essentially an extension of the placenta, providing the embryo with nutrients until the amniotic cavity becomes large enough to take over later in development.[2][5] Gradually, the coelomic cavity shrinks as the amniotic cavity expands and completely disappears by week 12.[5][6] The primary function of amniotic fluid at this point in development is the expansion of the amniotic sac which allows room for the fetus to grow unimpeded [1].

Late Gestation

Once the coelomic fluid begins to disappear, the amniotic cavity takes over. In the early stages of gestation, the water in amniotic fluid is derived mostly from maternal serum; however, at 10 weeks, the fetus begins to produce urine which gets secreted into the amniotic sac. During late gestation (the second and third trimesters), as the amniotic fluid expands, fetal urine becomes the largest source to the amniotic fluid.[6] Lung secretions, gastrointestinal secretions, and excretions from the umbilical cord and placental surface contribute to the composition of amniotic fluid as well; however, lung secretions alone make up as much as one-third amniotic fluid.[4][7] Compared to the composition of yellow coelomic fluid early in pregnancy, amniotic fluid is less viscous and always clear due to its lower protein concentration. Amniotic fluid is 98% water and electrolytes, and signaling molecules, peptides, carbohydrates, lipids and hormones make up the other 2%.[2][4]

Pathophysiology

Homeostasis of body fluids is important in the growing fetus. In addition to the constant circulation of amniotic fluid through inhalation and exhalation, there must be a balance between fluid formation and elimination.[4] The formation originates from fetal urine and lung secretions; however, elimination which is important for balance and homeostasis is largely the result of fetal swallowing and intramembranous absorption.[7][8] Early in pregnancy, embryonic skin is just simple epithelium, allowing fluid to pass freely under hydrostatic and osmotic forces [3]. Furthermore, its composition is similar to the fetus and maternal serum; it freely diffuses through fetal skin as well as the chorionic villi up until week 8. Eventually, fetal skin begins to become stratified epithelium and becomes fully keratinized by 25 weeks.[4][9] Once the skin of the fetus is fully keratinized later in pregnancy, it can no longer absorb or transfer fluids as easily back and forth. Respiration, swallowing, and urination are the main routes of exchange between the fetus and amniotic fluid to keep the balance of fluids [3]. The two largest contributors to elimination are fetal swallowing and the intramembranous pathway. Though there are many mechanisms of elimination of amniotic fluid, the greatest contributor to amniotic fluid elimination is through fetal swallowing, seen as early as 11 weeks.[10][11]

Clinical Significance

Abnormally high or low amniotic fluid volumes have shown to predict poor fetal outcomes; therefore, a normal amount of amniotic fluid volume is crucial to the healthy development of the fetus or embryo. Amniotic fluid has proven to be a major diagnostic tool when monitoring the progression and health of a pregnancy. Clinicians can use what is called the amniotic fluid index (AFI) or single deepest pocket (SDP).[12][13] These measurements are part of the biophysical profile that consists of fetal tone, fetal breathing, and a non-stress test.  AFI and SDP are estimations of amniotic fluid volume based on ultrasound measurements. An AFI of greater than 24 cm or SDP more than 8 cm is considered polyhydramnios which is an increased amount of amniotic fluid. Polyhydramnios can cause complications such as gastrointestinal tract obstruction, genetic disorders, musculoskeletal disorders, or congenital diaphragmatic hernias.[13] Conversely, oligohydramnios is an AFI under 5cm or SDP less than 2 cm.[14] Oligohydramnios can cause complications such as renal agenesis, genitourinary tract obstruction, and IUGR.[15][16] Clinicians can also use the hormones, peptides, and proteins of amniotic fluid to screen for genetic diseases.[2] Additionally, invasive testing may be required to obtain information rather than ultrasound, coined an amniocentesis. An amniocentesis is a procedure performed after 15 weeks that takes a sample of amniocytes and is used to diagnose chromosomal abnormalities such as Trisomy 21 (Down syndrome). This procedure, however, is much more invasive than other screening tests and can result in spontaneous miscarriage in 0.5 to 1% of pregnancies.[17] Further studies on the amniotic fluid are in motion; it remains a vital substance required for the embryo or fetus to survive and helps clinicians make decisions regarding are and predict outcomes of pregnancies.


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Embryology, Amniotic Fluid - Questions

Take a quiz of the questions on this article.

Take Quiz
How much of the composition of amniotic fluid is composed of water?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A primigravid female at 28 weeks presents to the pregnancy clinic for a scheduled visit. Her last visit was six weeks ago and was unremarkable. She does not have any active complaints. An ultrasound performed during this visit shows an amniotic fluid index of 26 cm. The patient is at the highest risk for which of the following complications?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 7-week old embryo is noted to not be progressing because the coelomic cavity has failed to develop. What other structures are likely going to fail to develop?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A primigravid female presents to the clinic for her 32 weeks appointment. Her last visit was at 28 weeks and was within normal limits. She has no active complaints. Upon ultrasound, she is noted to have an AFI of 5. Which of the following is the best next step in the management of this patient?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 37-year-old primigravid female presents to the clinic for a regular follow up at five weeks. She is very concerned about her baby possibly having Down syndrome or trisomy 21 due to her age. She wants whatever test that can be done at the earliest to confirm if the fetus has the chromosomal abnormality or not. Which of the following is the best next step in the management of this patient?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 24-year-old woman presents to her physician after a positive home pregnancy test. Based on her last menstrual period date and ultrasound, her estimated gestational age is 9 weeks. The presence of what characteristic in the embryo accounts for the homeostasis of amniotic fluid during this stage of her pregnancy?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 29-year-old female presents to her first prenatal visit after a positive home pregnancy test. She has already started prenatal vitamins and has no complaints today. Ultrasound confirms a 7-week intrauterine pregnancy. The structure providing the nutrients to the growing embryo derives from which of the following?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Embryology, Amniotic Fluid - References

References

ten Broek CM,Bots J,Varela-Lasheras I,Bugiani M,Galis F,Van Dongen S, Amniotic fluid deficiency and congenital abnormalities both influence fluctuating asymmetry in developing limbs of human deceased fetuses. PloS one. 2013;     [PubMed]
Tong XL,Wang L,Gao TB,Qin YG,Qi YQ,Xu YP, Potential function of amniotic fluid in fetal development---novel insights by comparing the composition of human amniotic fluid with umbilical cord and maternal serum at mid and late gestation. Journal of the Chinese Medical Association : JCMA. 2009 Jul;     [PubMed]
Beall MH,van den Wijngaard JP,van Gemert MJ,Ross MG, Amniotic fluid water dynamics. Placenta. 2007 Aug-Sep;     [PubMed]
Suliburska J,Kocyłowski R,Komorowicz I,Grzesiak M,Bogdański P,Barałkiewicz D, Concentrations of Mineral in Amniotic Fluid and Their Relations to Selected Maternal and Fetal Parameters. Biological trace element research. 2016 Jul;     [PubMed]
Jauniaux E,Gulbis B, Fluid compartments of the embryonic environment. Human reproduction update. 2000 May-Jun;     [PubMed]
Calleja-Agius J,Muttukrishna S,Jauniaux E, The effect of coelomic fluid on the production of cytokines by the first trimester human placenta. Placenta. 2011 Nov;     [PubMed]
Laudy JA,Wladimiroff JW, The fetal lung. 1: Developmental aspects. Ultrasound in obstetrics     [PubMed]
Gilbert WM,Brace RA, Amniotic fluid volume and normal flows to and from the amniotic cavity. Seminars in perinatology. 1993 Jun;     [PubMed]
Dale BA,Holbrook KA,Kimball JR,Hoff M,Sun TT, Expression of epidermal keratins and filaggrin during human fetal skin development. The Journal of cell biology. 1985 Oct;     [PubMed]
Brace RA, Physiology of amniotic fluid volume regulation. Clinical obstetrics and gynecology. 1997 Jun;     [PubMed]
Grassi R,Farina R,Floriani I,Amodio F,Romano S, Assessment of fetal swallowing with gray-scale and color Doppler sonography. AJR. American journal of roentgenology. 2005 Nov;     [PubMed]
Campbell J,Wathen N,Macintosh M,Cass P,Chard T,Mainwaring Burton R, Biochemical composition of amniotic fluid and extraembryonic coelomic fluid in the first trimester of pregnancy. British journal of obstetrics and gynaecology. 1992 Jul;     [PubMed]
Kornacki J,Adamczyk M,Wirstlein P,Osiński M,Wender-Ożegowska E, Polyhydramnios - frequency of congenital anomalies in relation to the value of the amniotic fluid index. Ginekologia polska. 2017;     [PubMed]
Rabie N,Magann E,Steelman S,Ounpraseuth S, Oligohydramnios in complicated and uncomplicated pregnancy: a systematic review and meta-analysis. Ultrasound in obstetrics     [PubMed]
Moore TR, The role of amniotic fluid assessment in evaluating fetal well-being. Clinics in perinatology. 2011 Mar;     [PubMed]
Kehl S,Schelkle A,Thomas A,Puhl A,Meqdad K,Tuschy B,Berlit S,Weiss C,Bayer C,Heimrich J,Dammer U,Raabe E,Winkler M,Faschingbauer F,Beckmann MW,Sütterlin M, Single deepest vertical pocket or amniotic fluid index as evaluation test for predicting adverse pregnancy outcome (SAFE trial): a multicenter, open-label, randomized controlled trial. Ultrasound in obstetrics     [PubMed]
Harraway J, Non-invasive prenatal testing. Australian family physician. 2017 Oct;     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Nurse-Maternal Newborn PN. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Nurse-Maternal Newborn PN, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Nurse-Maternal Newborn PN, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Nurse-Maternal Newborn PN. When it is time for the Nurse-Maternal Newborn PN board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Nurse-Maternal Newborn PN.