AMNIOTIC FLUIDAMNIOTIC FLUID

By La Lura White MD

Maternal Fetal Medicine

AMNIOTIC FLUID

The amniotic fluid that bathes the fetus is necessary for its proper growth and development.

It cushions the fetus from physical trauma Provides a barrier against infection Allowing 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 FLUID Cleavage of zygote Zygote begins cleavage in the

fallopian tube s/p 3 days in the fallopian tube,

the morula enters uterine cavity After 3 days floating in the

uterine cavity it will implant Gradual accumulation of fluid

between blastomeres within the morula results in the formation of the blastocyst

Inner cell mass-embryo Outer cell mass-trophoblast

AMNIOTIC FLUID

7 1/2 days: Trophoblast Cytotrophoblast: individual, pale staining cells Syncytiotrophoblast: dark staining nuclei within

an amorphous common cytoplasm Inner cell mass: embryonic disc thick ectoderm

and underlying endoderm Between the embryonic disc and the trophoblast,

small cells appear that enclose a space that will become the amniotic cavity

AMNIOTIC FLUID

AMNIOTIC FLUID

AMNIOTIC FLUID

Small cells line the inner surface of the trophoblast called amniogenic cells, later to become amniotic epithelium

The amnion develops by the 7-8 th day Derived from fetal ectoderm As the amnion enlarges, it gradually engulfs the embryo

which prolapses into its cavity Distention of the amniotic sac brings it in contact with the

chorion laeve The chorion and amnion are juxtaposed but not connected

AMNIOTIC FLUID

AMNIOTIC FLUID

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

50 ml 12 weeks 400 ml midpregnancy 800 ml 34 weeks 1000ml 36-38 weeks At full term, there is between 500-

1000 cc of amniotic fluid.

AMNIOTIC FLUID

AMNIOTIC FLUID

AMNIOTIC FLUID

Composition and volume of amniotic fluid changes as pregnancy advances

In the first half of pregnancy, the fluid is the same as the extracellular fluid of the fetus, devoid of particulate matter

Produced by amniotic membranes Fluid also passes across fetal skin

AMNIOTIC FLUID

By the fourth month, the fetus contributes to amniotic fluid via:

urinating swallowing movement of fluid in and out of the respiratory

tract Fetal urination will eventually comprise the

majority of the amniotic fluid

AMNIOTIC FLUID

The 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 concentration

Contains more urea, creatinine and uric acid Osmolality decrease with increasing gestational age

AMNIOTIC FLUID

An important function of the fetal kidney is to maintain a urine output sufficient to maintain amniotic fluid volume

Daily urine production is approximately 30% of fetal weight

The 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 FLUID

The 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 FLUID Pathway Volume (ml)/day to the fetus to amniotic fluid Fetal 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 FLUID

Glycerophospholipids (lecithin, sphingomyelin) from the lungs accumulate in AF

Desquamated fetal cells, lanugo, scalp hair and vernix caseosa are shed

Also contains albumin, urea, uric acid, creatinine,, bilirubin, fat, fructose, leukocytes, proteins, epithelial cells, enzymes

AMNIOTIC FLUID

Amniotic 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 centimeters

– Cord containing pocket < 30%

– The total volume is calculated by adding these values – <5 oligohydramnios

AMNIOTIC FLUID

The 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 FLUID

– 6-8 borderline AFI– 8-24 normal– >24 polyhydramnios

AMNIOTIC FLUID

Oligohydramnios Normal

AMNIOTIC FLUID

Polyhydramnios 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 pregnancies Preterm 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 anomalies

80-90% are idiopathic In 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 FLUID

Fetal akinesia syndrome: Absence of swallowing

Blockage of the fetus' gastrointestinal tract Esophageal atresia (usually associated with

a tracheoesophageal fistula) Tracheal agenesis Duodenal atresia.

AMNIOTIC FLUID

– Non-genetic– Congenital cardiac-rhythm anomalies

associated with hydrops, fetal-to-maternal hemorrhage, and parvovirus infection

– Maternal type 2 diabetes mellitus– Multiple gestations

AMNIOTIC FLUID

Polyhydramnios: treatment– Patients 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 FLUID

Polyhydramnios Treat underlying cause

Fetal anemia: Fetal transfusion Diabetes: control blood sugar Twin-Twin Transfusion: ablation

AMNIOTIC FLUID

Polyhydramnios: Treatment Procedures:

– 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 FLUID Most cases of polyhydramnios respond in the first week of

treatment with indomethacin The 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 Name Indomethacin (Indocin) -- Rapidly absorbed; metabolism occurs

in liver by demethylation, deacetylation, and glucuronide conjugation

Inhibits prostaglandin synthesis. Adult Dose25 mg PO q6h

AMNIOTIC FLUID Contraindications Documented hypersensitivity; GI bleeding; renal

insufficiency Interactions: Co administration with aspirin increases risk of serious

NSAID-related adverse effects Probenecid may increase concentrations and, possibly,

toxicity of NSAIDs Decrease effect of hydralazine, captopril, and beta-blockers Decrease diuretic effects of furosemide and thiazides Monitor PT closely (instruct patients to watch for signs of

bleeding) Increase risk of methotrexate toxicity Increase phenytoin levels when administered concurrently

AMNIOTIC FLUID

Usually safe but benefits must outweigh the risks Can cause fetal renal and CNS complications; associated with

premature closure of the fetal ductus arteriosus when administered near term

Periventricular 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 FLUID

Oligohydramnios occurs in 4% of pregnancies Sonographically 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 hypoplasia

Rupture of the membranes is the most common cause of oligohydramnios and if prolonged can result in chorio

AMNIOTIC FLUID

Oligohydramnios– Fetal urinary tract anomalies, such as renal agenesis

(Potter’s 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' gestation

– Maternal use of prostaglandin synthase inhibitors or angiotensin-converting enzyme (ACE) inhibitors

AMNIOTIC FLUID

Severe oligohydramnios– Marked deformation of the fetus due to of intrauterine constraint – External compression with a flattened facies– Epicanthal folds– Hypertelorism– Low-set ears– Mongoloid slant of the palpebral fissure– Crease below the lower lip– Micrognathia– Thoracic compression – Bowed legs– Clubbed feet

AMNIOTIC FLUID

The mortality rate in oligohydramnios is high

Pulmonary hypoplasia IUGR Meconium stainin Fetal heart conduction abnormalities Poor tolerance of labor Lower Apgar scores Fetal acidosis Physical deformities

AMNIOTIC FLUID

Oligohydramnios: Treatment Maternal 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 FLUID

Oligohydramnios: Treatment The transabdominal instillation of indigo carmine

may be used to evaluate for PROM The 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 FLUID

15 week fetus with posterior urethral valves.

The fetus is in breech presentation. The bladder (b) is massively distended.

AMNIOTIC FLUID

15 week fetus with posterior urethral valves.

) Enlarged "key-hole" bladder associated with posterior urethral valves.

AMNIOTIC FLUID

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

AMNIOTIC FLUID

Mortality/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 FLUID

Amnionitic fluid evaluation allows assessment of the fetal intrauterine environment

Potentially invaluable information Requires close follow-up and evaluation

secondopinion2.com info@secondopinion2.com