In-Depth Notes on Amniotic Fluid and Its Disorders

Polyhydramnios

Definition: Amniotic Fluid Index (AFI) ≥ 25 cm, or Single Largest Vertical Pocket (SVP) ≥ 8 cm, or absolute value of amniotic fluid is ≥ al.

  • Mechanisms:

    1. Excessive urine production by fetus

    • Multifetal pregnancy

    • Twin-to-twin transfusion syndrome (one fetus experiences oligohydramnios, while the other has polyhydramnios).

    • Maternal diabetes leading to fetal hyperglycemia and increased fetal urination.

    • Fetal high cardiac output states due to various conditions (e.g., anemia, infections).

    1. Fetal anomalies & infections:

    • Conditions like parvovirus B19 and congenital issues such as alpha thalassemia and G6PD deficiency may induce severe polyuria, leading to polyhydramnios.

    • Chorangioma of the placenta can also contribute.

  • Consequences:

    • Respiratory difficulties: Can result when overdistended uterus pushes on the diaphragm.

    • Complications:

    • Preterm labor

    • Premature rupture of membranes (PROM) or preterm premature rupture of membranes (PPROM)

    • Abruptio placentae: leakage of fluid can lead to early detachment of placenta.

    • Postpartum hemorrhage (PPH) due to poor uterine tone.

Management of Polyhydramnios

  • For mild cases:

    • Often asymptomatic; generally no treatment is required.

  • For severe symptoms (SVP ≥ 16 cm, AFI ≥ 35 cm):

    • Amnioreduction: therapeutic amniocentesis to remove excess amniotic fluid.

    • Indication: Severe respiratory discomfort.

    • Procedure:

      • Performed under ultrasound guidance with 18 G spinal needle.

      • Fluid removal at a controlled rate (e.g., 2.5L at 1000ml in 20 min).

      • Complications: Preterm labor, infection, abruptio placenta, hypoproteinemia.

    • Tocolytics: can be used for uterine irritability leading to preterm labor, usually below 34 weeks (e.g., Indomethacin, Corticosteroids).

  • Delivery Timing:

    • Induction of labor for mild to moderate polyhydramnios at 39-40 weeks.

    • For severe cases, induction should be at 37 weeks.

Oligohydramnios

  • Definition: AFI ≤ 5 cm, Single Deepest Pocket (SDP) ≤ 2 cm, absolute value of liquor ≤ 200 ml.

  • Common Causes:

    • Idiopathic: Most common cause for mild oligohydramnios.

    • Severe oligohydramnios: Often due to fetal renal anomalies (e.g., renal agenesis, posterior urethral valves).

  • Other Causes:

    • Rupture of membranes

    • Uteroplacental insufficiency (e.g., hypertension in mother, IUGR)

    • Maternal medications (e.g., ACE inhibitors, Indomethacin).

    • TORCH infections: can cause placental calcification leading to oligohydramnios.

Consequences of Oligohydramnios

  • Moderate to Severe:

    1. Pulmonary hypoplasia: Most common complication.

    2. Limb deformities: Such as clubfoot (CTEV) or limb amputation.

    3. Cord compression: Leading to fetal distress.

    • Typical CTG finding: Variable decelerations.

  • Potter's syndrome: Severe oligohydramnios due to renal defects leads to characteristic facial features and lung hypoplasia.

Management of Oligohydramnios

  • Fetal Monitoring: From 32 weeks onwards, via NST and biophysical profile.

  • Termination of Pregnancy:

    • For mild complications: at 39 weeks.

    • Moderate/severe complications: between 36-37 weeks.

  • Enhance Maternal Hydration:

    • Amnioinfusion: To alleviate recurrent variable decelerations.

    • Monitoring for complications: Potential fetal distress or malformations.