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AMNIOTIC FLUID

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IMPORTANT TOPICS

• Amniotic fluid function• Clinical importance of AF• Volume and composition• Amniotic fluid abnormalities

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Amniotic fluid function:

• Allow room for fetal growth, movement and development.

• Ingestion into GIT→ growth and maturation.

• Fetal pulmonary development (20 weeks).

• Protects the fetus from trauma.

• Maintains temperature.

• Contains antibacterial activity.

• Aids dilatation of the cervix during labour.

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Clinical importance of AF:

• Screening for fetal malformation (serum α-fetoprotien).

• Assessment of fetal well-being (amniotic fluid index).

• Assessment of fetal lung maturity (L/S ratio).

• Diagnosis and follow up of labour.

• Diagnosis of PROM (ferning test).

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Amniotic fluid formation and composition:

• First & early second trimester : Amount is 5-50 ml & arises from:

- ultrafiltrate of Maternal plasma through the vascularized uterine decidua (in early pregnancy).

- Transudation of fetal plasma through the fetal skin & umbilical cord (up to 20 weeks' gestation).

* It is iso-osmolar with fetal & maternal plasma, though it is devoid of proteins.

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Volume and composition

• From 20 weeks up to term (mainly - fetal urine): At 18th week, the fetus voids 7-

14ml/day; at term fetal kidneys secretes 600-700ml of urine/day into AF.

- Fetal respiratory tract secretes 250ml/day into AF. - Fluid transfers across the placenta. - Fetal oro-nasal secretions.• Secretion is controlled by: - Fetal swallowing at term removes 500ml/day. - Reabsorption into maternal plasma (osmotic

gradient).• AF constituents: - urea, creatinine & uric acid + desquamated fetal

cells, vernix, lanugo hair & others→ hypo-osmolar amniotic fluid….

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Amniotic fluid volume :

• About 500 mls enter and leave the amniotic sac each hour.

• gradual ↑ up to 36 weeks to around 600 to 1000 ml then↓ after that.

• The normal range is wide but the approximate volumes are:

- 500 ml at 18 weeks

- 800 ml at 34 weeks.

- 600 ml at term.

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Amniotic fluid volume assessment

• Clinical assessment is unreliable.• Objective assessment depends on U/S to

measure:

- deepest vertical pool (DVP).

- Amniotic fluid index (AFI). It is a total of the DVPs in each four quadrants of the uterus. it is a more sensitive indicator of AFV throughout pregnancy.

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Amniotic fluid abnormalities

Oligohydramnios:

Defined as reduced amniotic fluid i.e. amniotic fluid index of 5 cm or less or the deepest vertical pool < 2 cm.

Polyhydramnios:

Defined as excessive amount of amniotic fluid of 2000 ml or more (AFI of > 25 cm or the deepest vertical pool of > 8 cm) .

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Causes of oligohydramnios:Causes of oligohydramnios:

1. Fetal causes:

* Renal cause (57%):

- Renal agenesis (Potter’s syndrome).

- polycystic kidney.

- Urethral obstruction (atresia/posterior urethral valve).

* Fetal growth restriction.

* Fetal death.

* Postterm pregnancy.

* Preterm premature rupture membranes

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Causes of oligohydramnios:Causes of oligohydramnios:

2. Maternal causes:• Uteroplacental insufficiency.• Preeclampsia.

3. Placental causes:• twin-twin transfusion.

4. Drug causes: Prostaglandin synthase inhibitor as NSAID.

• 5. Idiopathic

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Complications of oligohydramnios:Complications of oligohydramnios:

• In early pregnancy:• Amniotic adhesions or bands→

amputation/death.• Pressure deformities (club feet).• Pulmonary hypoplasia:

- Thoracic compression.

- No breathing movement.

- No amniotic fluid retain. Flattened face. Postural deformities.

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• In late pregnancy:• Fetal growth restriction.• Placental abruption.• Preterm labour.• Fetal distress.• Fetal death.• Meconium aspiration.• Labour induction/CS.

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Oligohydramnios:

Diagnosis:

- Fundal > date.- AF I < 5CM , DVP < 2.

- IUGR: abdominal circumference < 10th centile.- Doppler abnormalities- Congenital fetal anomalies.

Management:- Treat the cause (pprom, preeclampsia).- Assess fatal wellbeing (U/S/CTG/Doppler/BPP).- Vesicoamniotic shunting (urethral obstruction).- Amnioinfusion (no↓ in fetal death).

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Polyhydramnios

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Polyhydramnios

types

1. Mild hydramnios (80%):

a pocket of amniotic fluid measuring 8 to 11 cm.

2. moderate hydramnios (15%):

a pocket of amniotic fluid measuring 12 to 15 cm.

3. Severe hydramnios (5%) - twin-twin transfusion syndrome :

a pocket of amniotic fluid measuring 16 cm or more.

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Causes of polyhydramnios

• Fetal malformation:

- GIT: esophageal/duodenal atresia, tracheoesophageal fistula.

- CNS: anencephaly (↓swallowing, exposed meninges, no antidiuretic hormone).

• Twin-twin transfusion → fetal polyuria.

• Hydrops fetalis: congestive heart failure, severe anaemia or hypoproteinemia → placental transudation

• diabetes mellitus (osmotic diuresis).

• Idiopathic.

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diagnosis of polyhydramnios

• Symptoms:- dyspnea. - edema. - abdominal distention - preterm labour.• Abdominal examination: - ↑uterus than expected. - difficult to palpate fetal

parts. - difficult to hear fetal heart

sound. - ballotable fetus.

• Ultrasound:

- excessive amniotic fluid.

- fetal abnormalities.

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management

• Minor degrees: no treatment.• Bed rest, diuretics, water and salt restriction:

ineffective.• Hospitalization: dyspnea, abdominal pain or difficult

ambulation.• Endomethacin therapy: . - impairs lung liquid production/enhances absorption. - ↓fluid movement across fetal membranes. * complications: premature closure of ductus

arteriosus, impairment of renal function, and cerebral vasoconstriction. So not used after 35 weeks

• Amniocentesis: to relieve maternal distress and to test for fetal lung maturity. Complications: ruptured membrane, chorioamnionitis, placental abruption, preterm labour.

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