AMNIOTIC FLUIDBy La Lura White MDMaternal Fetal Medicine

AMNIOTIC FLUIDThe amniotic fluid that bathes the fetus is necessary for its proper growth and development.It cushions the fetus from physical traumaProvides a barrier against infectionAllowing for freedom of fetal movement and permitting symmetrical musculoskeletal development Maintaining a relatively constant temperature for the environment surrounding the fetus, thus protecting the fetus from heat loss Permitting proper lung development

AMNIOTIC FLUIDCleavage of zygoteZygote begins cleavage in the fallopian tubes/p 3 days in the fallopian tube, the morula enters uterine cavity After 3 days floating in the uterine cavity it will implantGradual accumulation of fluid between blastomeres within the morula results in the formation of the blastocystInner cell mass-embryoOuter cell mass-trophoblast

AMNIOTIC FLUID7 1/2 days: TrophoblastCytotrophoblast: individual, pale staining cellsSyncytiotrophoblast: dark staining nuclei within an amorphous common cytoplasmInner cell mass: embryonic disc thick ectoderm and underlying endodermBetween the embryonic disc and the trophoblast, small cells appear that enclose a space that will become the amniotic cavity

AMNIOTIC FLUID

AMNIOTIC FLUID

AMNIOTIC FLUIDSmall cells line the inner surface of the trophoblast called amniogenic cells, later to become amniotic epitheliumThe amnion develops by the 7-8 th dayDerived from fetal ectodermAs the amnion enlarges, it gradually engulfs the embryo which prolapses into its cavityDistention of the amniotic sac brings it in contact with the chorion laeveThe chorion and amnion are juxtaposed but not connected

AMNIOTIC FLUID

AMNIOTIC FLUIDClear fluid collects within the amniotic cavity and increases with gestational age. Normal amniotic fluid levels vary.

50 ml 12 weeks400 ml midpregnancy800 ml 34 weeks1000ml 36-38 weeksAt full term, there is between 500-1000 cc of amniotic fluid.

AMNIOTIC FLUID

AMNIOTIC FLUID

AMNIOTIC FLUIDComposition and volume of amniotic fluid changes as pregnancy advancesIn the first half of pregnancy, the fluid is the same as the extracellular fluid of the fetus, devoid of particulate matterProduced by amniotic membranesFluid also passes across fetal skin

AMNIOTIC FLUIDBy the fourth month, the fetus contributes to amniotic fluid via:urinatingswallowingmovement of fluid in and out of the respiratory tractFetal urination will eventually comprise the majority of the amniotic fluid

AMNIOTIC FLUIDThe fetal kidneys start to develop during the 4th and 5th weeks of gestation and begin to excrete urine into the amniotic fluid at the 8th to 11th week At the 20th week the fetal kidneys produce most of the amniotic fluid Fetal urine is hypotonic (c/w plasma) because of lower electrolyte concentrationContains more urea, creatinine and uric acidOsmolality decrease with increasing gestational age

AMNIOTIC FLUIDAn important function of the fetal kidney is to maintain a urine output sufficient to maintain amniotic fluid volumeDaily urine production is approximately 30% of fetal weightThe excreted urine does not serve real excretory or homeostatic function because the urine, via the amniotic fluid, is recycled back to the fetus by swallowing (25% of fetal weight)

AMNIOTIC FLUIDThe factors involved in regulating amniotic fluid volume are still not completely understood. The 6 proposed pathways (Brace, 1997) for fluid movement into and out of the amniotic cavity include:

AMNIOTIC FLUIDPathway Volume (ml)/day to the fetus to amniotic fluidFetal swallowing 500-1000

Oral secretions 25

Secretions from the respiratory tract 170 170

Fetal urination 800-1200

Intramembranous flow across the placenta, umbilical cord 200-500

Transmembraneous flow from the amniotic cavity into the uterine circulation 10

AMNIOTIC FLUIDGlycerophospholipids (lecithin, sphingomyelin) from the lungs accumulate in AFDesquamated fetal cells, lanugo, scalp hair and vernix caseosa are shedAlso contains albumin, urea, uric acid, creatinine,, bilirubin, fat, fructose, leukocytes, proteins, epithelial cells, enzymes

AMNIOTIC FLUIDAmniotic fluid volume (AFI)The volume of the amniotic fluid is evaluated by visually dividing the mother's abdomen into 4 quadrants The largest vertical pocket of fluid in each quadrant is measured in centimetersCord containing pocket < 30%

The total volume is calculated by adding these values

AMNIOTIC FLUIDThe 2 cm x 2 cm pocket definition (Magann, 1999a) and an AFI < 5 cm (Horsager, 1994) were compared to the actual amniotic fluid volume as measured by a dye-dilution technique. The single 2 cm pocket had a sensitivity of 9.5% AFI < 5.0 cm had a sensitivity of 18% for the detection of oligohydramnios

AMNIOTIC FLUID6-8 borderline AFI8-24 normal>24 polyhydramnios

AMNIOTIC FLUIDOligohydramnios Normal

AMNIOTIC FLUIDPolyhydramnios is usually defined as;Amniotic fluid index (AFI) more than 24 cm Single pocket of fluid at least 8 cm in deep that results in more than 2000 mL of fluid Occurs in 1% of pregnanciesPreterm labor and delivery occurs in approximately 26% of mothers with polyhydramnios. Other complications are premature rupture of the membranes (PROM), abruptio placenta, malpresentation, cesarean delivery, and postpartum hemorrhage

AMNIOTIC FLUID

An abnormally high level of amniotic fluid, polyhydramnios, alerts the clinician to possible fetal anomalies80-90% are idiopathicIn pregnancies affected by polyhydramnios, approximately 20% of the neonates are born with a congenital anomaly of some type Gastrointestinal system (40%), central nervous system (26%), cardiovascular system (22%), genitourinary system (13%) and 50% of the patients had no associated risk factors.

AMNIOTIC FLUIDFetal akinesia syndrome: Absence of swallowingBlockage of the fetus' gastrointestinal tractEsophageal atresia (usually associated with a tracheoesophageal fistula)Tracheal agenesisDuodenal atresia.

AMNIOTIC FLUIDNon-geneticCongenital cardiac-rhythm anomalies associated with hydrops, fetal-to-maternal hemorrhage, and parvovirus infectionMaternal type 2 diabetes mellitusMultiple gestations

AMNIOTIC FLUIDPolyhydramnios: treatmentPatients with polyhydramnios tend to have a higher incidence of preterm labor secondary to overdistention of the uterus. Schedule weekly or twice weekly perinatal visits and cervical examinations. Place patients on bed rest to decrease the likelihood of preterm labor. Perform serial ultrasonography to determine the AFI and document fetal growth.

AMNIOTIC FLUIDPolyhydramniosTreat underlying cause

Fetal anemia: Fetal transfusionDiabetes: control blood sugarTwin-Twin Transfusion: ablation

AMNIOTIC FLUIDPolyhydramnios: TreatmentProcedures: Reductive amniocentesis may be performed and has contributed to prolonged pregnancy in patients who are severely affected by hydramnios.This procedure can reduce the risk of preterm labor, PROM, umbilical cord prolapse, and placental abruption.However, if too much fluid is removed, the risk of placental abruption due to uterine compression increases.Other risks of the procedure include infection, bleeding, and trauma to the fetus. Laser ablation of placental vessels may be efficacious in cases of fetal-fetal transfusion syndrome

AMNIOTIC FLUIDMost cases of polyhydramnios respond in the first week of treatment with indomethacinThe approach appears to be highly effective (90-100% in some studies), provided that the cause is not hydrocephalus or a neuromuscular disorder that alter fetal swallowing.Drug Category: Prostaglandin inhibitors -- When administered to pregnant women with polyhydramnios, these drugs can reduce fetal urinary flow, decreasing the volume of amniotic fluid. Drug NameIndomethacin (Indocin) -- Rapidly absorbed; metabolism occurs in liver by demethylation, deacetylation, and glucuronide conjugation Inhibits prostaglandin synthesis. Adult Dose25 mg PO q6h

AMNIOTIC FLUIDContraindicationsDocumented hypersensitivity; GI bleeding; renal insufficiency Interactions: Co administration with aspirin increases risk of serious NSAID-related adverse effectsProbenecid may increase concentrations and, possibly, toxicity of NSAIDsDecrease effect of hydralazine, captopril, and beta-blockersDecrease diuretic effects of furosemide and thiazidesMonitor PT closely (instruct patients to watch for signs of bleeding)Increase risk of methotrexate toxicityIncrease phenytoin levels when administered concurrently

AMNIOTIC FLUIDUsually safe but benefits must outweigh the risksCan cause fetal renal and CNS complications; associated with premature closure of the fetal ductus arteriosus when administered near termPeriventricular leukomalacia has been reported in infants whose mothers have received indomethacin as a tocolytic.Acute renal insufficiency, hyperkalemia, hyponatremia, interstitial nephritis, and renal papillary necrosis may occur; increases risk of acute renal failure in patients with preexisting renal disease or compromised renal perfusion;Reversible leukopenia may occur (discontinue if persistent leukopenia, granulocytopenia, or thrombocytopenia present).

AMNIOTIC FLUIDOligohydramnios occurs in 4% of pregnanciesSonographically defined as an AFI less than 5 cm or the absence of a fluid pocket 2-3 cm in depth.Inadequate levels of amniotic fluid, oligohydramnios, results in poor development of the lung tissue and can lead to fetal death secondary to bronchopulmonary dysplasia (BPD) and pulmonary hypoplasiaRupture of the membranes is the most common cause of oligohydramnios and if prolonged can result in chorio

AMNIOTIC FLUIDOligohydramniosFetal urinary tract anomalies, such as renal agenesis (Potters syndrome), polycystic kidneys, or any urinary obstructive lesion (eg, posterior urethral valves)Placental insufficiency, as seen in PIH, maternal diabetes, or postmaturity syndrome when the pregnancy extends beyond 42 weeks' gestationMaternal use of prostaglandin synthase inhibitors or angiotensin-converting enzyme (ACE) inhibitors

AMNIOTIC FLUIDSevere oligohydramniosMarked deformation of the fetus due to of intrauterine constraint External compression with a flattened faciesEpicanthal foldsHypertelorismLow-set earsMongoloid slant of the palpebral fissureCrease below the lower lipMicrognathiaThoracic compression Bowed legsClubbed feet

AMNIOTIC FLUIDThe mortality rate in oligohydramnios is high

Pulmonary hypoplasiaIUGRMeconium staininFetal heart conduction abnormalitiesPoor tolerance of laborLower Apgar scoresFetal acidosisPhysical deformities

AMNIOTIC FLUIDOligohydramnios: TreatmentMaternal bed rest and hydration promote the production of amniotic fluid by increasing the maternal intravascular space. Bed rest may also help when PIH is present, allowing prolongation of the pregnancy.Oral hydration

AMNIOTIC FLUIDOligohydramnios: TreatmentThe transabdominal instillation of indigo carmine may be used to evaluate for PROMThe transcervical instillation of isotonic sodium chloride solution (ie, amnioinfusion) at the time of delivery reduces the risk of cord compression, fetal distress and meconium dilution. It also reduces the potential need for cesarean delivery.

AMNIOTIC FLUID15 week fetus with posterior urethral valves. The fetus is in breech presentation. The bladder (b) is massively distended.

AMNIOTIC FLUID15 week fetus with posterior urethral valves. ) Enlarged "key-hole" bladder associated with posterior urethral valves.

AMNIOTIC FLUID19 week fetus with Turner's syndrome, cystic hygroma (arrows) and oligohydramnios

AMNIOTIC FLUIDMortality/Morbidity: Chamberlin used ultrasonography to evaluate the perinatal mortality rate (PMR) in 7562 patients with high-risk pregnancies. The PMR of patients with normal fluid volumes was 1.97 deaths per 1000 patients.The PMR increased to 4.12 deaths per 1000 patients with polyhydramnios 56.5 deaths per 1000 patients with oligohydramnios

AMNIOTIC FLUIDAmnionitic fluid evaluation allows assessment of the fetal intrauterine environmentPotentially invaluable informationRequires close follow-up and evaluation

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