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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.
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….
Amniotic fluid volume :
• About 500mls 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
- 500 ml at 18 weeks
- 800 ml at 34 weeks.
- 600 ml at term.
Amniotic fluid function:
1. Allow room for fetal growth, movement and development.
2. Ingestion into GIT→ growth and maturation.
3. Fetal pulmonary development (20 weeks).
4. Protects the fetus from trauma.
5. Maintains temperature.
6. Contains antibacterial activity.
7. Aids dilatation of the cervix during labour.
Clinical importance of AF:
1. Screening for fetal malformation (serum α-
2. Assessment of fetal well-being (amniotic fluid
3. Assessment of fetal lung maturity (L/S ratio).
4. Diagnosis and follow up of labour.
5. Diagnosis of PROM (ferning test).
Amniotic fluid volume assessment
•Clinical assessment is unreliable.
•Objective assessment depends on U/S to
- 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
Amniotic fluid abnormalities
Defined as reduced amniotic fluid of 200ml or less i.e.
amniotic fluid index of 5 cm or less or the deepest
vertical pool < 2 cm.
Defined as excessive amount of amniotic fluid of
2000ml or more (AFI of > 25 cm or the deepest
vertical pool of > 8 cm) .
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
a pocket of amniotic fluid measuring 16 cm or more.
•Problems with swallowing and GI absorption
•Increased transudation of fluid:
•anencephaly, spina bifida
•Increased urination: anencephaly (lack of ADH,
stimulation of urination centers)
Complications of oligohydramnios:
In early pregnancy:
•Amniotic adhesions or bands→ amputation/death.
•Pressure deformities (club feet).
- Thoracic compression.
- No breathing movement.
- No amniotic fluid retain.
In late pregnancy:
•Fetal growth restriction.
• Extremely poor fetal prognosis, especially in early
• Adhesions between amnion and fetal parts ---
malformations and amputations
• Musculoskeletal deformities
• Pulmonary hypoplasia
• Cord Compression -- >fetal hypoxia
• Passage of meconium into low AF volume: thick
particulate suspension -->respiratory compromise
• 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,