Amniotic Fluid & Its Functions
- Produced by fetal kidneys & lungs, absorbed by fetal swallowing.
- Normal Amniotic Fluid Index (AFI):
- 5–25 cm (Measured via ultrasound).
- Functions:
- Protects the fetus from trauma.
- Allows lung development & movement.
- Prevents umbilical cord compression.
Polyhydramnios (Excess Amniotic Fluid)
Definition:
- Excessive accumulation of amniotic fluid (AFI >25 cm or Deepest Pocket >8 cm).
Types:
- Acute Polyhydramnios: Develops rapidly in 2nd trimester (Severe cases).
- Chronic Polyhydramnios: Gradual increase in amniotic fluid over weeks/months.
Causes of Polyhydramnios:
Maternal Causes:
- Diabetes Mellitus (Most Common) → Fetal polyuria due to hyperglycemia.
- Rh Isoimmunization → Fetal anemia leads to increased urine output.
Fetal Causes:
- Fetal Anomalies (Impaired Swallowing):
- Esophageal or Duodenal Atresia.
- Anencephaly (Absent swallowing reflex).
- Multiple Pregnancy (Twin-to-Twin Transfusion Syndrome - TTTS).
- Hydrops Fetalis (Severe Fetal Anemia, Heart Failure).
Clinical Features:
- Maternal discomfort (Abdominal distension, Shortness of breath).
- Difficulty in palpating fetal parts due to excess fluid.
- Increased risk of preterm labor, PPROM.
Diagnosis:
- Ultrasound: AFI >25 cm or Deepest Pocket >8 cm.
- Glucose Tolerance Test (For Maternal Diabetes).
- TORCH Screening (For Infections like CMV, Toxoplasmosis).
Complications of Polyhydramnios:
- Maternal:
- Preterm labor, PPROM.
- Respiratory distress (Pressure on diaphragm).
- Fetal:
- Cord prolapse (If membranes rupture).
- Malpresentations (Breech, Transverse).
Management:
- Mild Cases: Monitor AFI every 1–2 weeks.
- Severe Cases:
- Amnioreduction (Drain excess fluid via amniocentesis).
- Indomethacin (NSAID) to reduce fetal urine production (Not after 32 weeks).
- Delivery Planning:
- Induction at term if stable.
- C-section if malpresentation or fetal distress.
Oligohydramnios (Low Amniotic Fluid)
Definition:
- AFI <5 cm or Deepest Pocket <2 cm on ultrasound.
Causes of Oligohydramnios:
Maternal Causes:
- Hypertension & Preeclampsia (Most Common) → Reduced placental perfusion.
- Dehydration, Uteroplacental Insufficiency.
Fetal Causes:
- Renal Abnormalities (Decreased Urine Production):
- Renal Agenesis (Potter Syndrome).
- Posterior Urethral Valves (Bladder Outlet Obstruction).
- Post-Term Pregnancy (Aging Placenta reduces fluid).
- IUGR (Placental Insufficiency reduces fluid).
Clinical Features:
- Reduced fetal movements.
- Small-for-dates uterus.
- Difficult fetal palpation (Tightly compressed fetus).
Diagnosis:
- Ultrasound: AFI <5 cm or Deepest Pocket <2 cm.
- Doppler Studies: Assess fetal circulation in placental insufficiency.
Complications of Oligohydramnios:
- Maternal:
- Prolonged labor (Poor lubrication).
- Fetal:
- Pulmonary hypoplasia (If early onset).
- Cord compression → Fetal distress (Variable decelerations on CTG).
Management:
- Mild Cases (AFI 5–8 cm): Hydration, Weekly AFI monitoring.
- Severe Cases (AFI <5 cm):
- Amnioinfusion (Inject fluid into amniotic sac during labor).
- Early delivery if fetal distress or IUGR.
Summary Table: Polyhydramnios vs. Oligohydramnios
|
Feature |
Polyhydramnios |
Oligohydramnios |
|
Definition |
AFI >25 cm |
AFI <5 cm |
|
Common Causes |
Diabetes, Twin-to-Twin Transfusion, Anomalies |
Preeclampsia, Renal Agenesis, IUGR |
|
Complications |
Preterm labor, Cord prolapse |
Fetal distress, Pulmonary hypoplasia |
|
Management |
Amnioreduction, NSAIDs |
Amnioinfusion, Early delivery if needed |
Key Takeaways
- Polyhydramnios is linked to diabetes & fetal swallowing issues.
- Oligohydramnios is commonly due to placental insufficiency or fetal kidney defects.
- Severe cases of both require intervention (Amnioreduction or Amnioinfusion).
- Fetal monitoring is crucial to prevent complications.
