Overview

• Amniotic Fluid → largely comes from foetal urine from 2nd trimester onwards.
• Oligohydramnios → decreased volume of amniotic fluid (<5th centile for gestational age). Affects 4% of pregnancies. Either increased loss (ROM) or decreased production (TTTS, urinary tract pathology, placental insufficiency).
  • Reduced urine production → placental insufficiency, pre-eclampsia, IUGR.
  • Reduced urine output from kidneys → maternal medications (e.g. NSAIDs/ACEi), renal agenesis (e.g. In potter's sequence - death in utero).
    • Can cause resultant pulmonary hypoplasia (fetal lungs require amniotic fluid to develop).
  • Loss of fluid → PROM, post-term pregnancy, TTTS in donor baby.
  • Chromosomal abnormalities.
• Polyhydramnios → increased volume of amniotic fluid (>95th centile for gestational age). Affects 1-4% of pregnancies. Either increased fetal urine production (GDM, TTTS) or reduced fetal swallowing (dudodenal atresia, bowel malformation, chromosomal abnormality, nerological issue).
  • Failure of foetal swallowing → neurological or GIT. Cycle of foetus urinating and then swallowing is disrupted. Gut (oesophageal) atresia.
  • Congenital infections.
  • Foetal polyuria.
  • Multiple Pregnancy → TTTS in recipient baby.
  • Gestational Diabetes → causes foetal polyuria.
  • Foetal Anaemia → increase in cardiac output, increases urine production.
  • Cleft Palate → impairs ability of fetus to swallow.

Making Diagnosis

Clinical Features

• Oligohydramnios
  • History of fluid leak PV (ROM).
  • Abdominal exam → decreased fundal height, foetal parts easily palpable.
• Polyhydramnios
  • Abdominal exam → increased fundal height, inpalpable foetal parts.

Investigations

• USS → liquour volume, foetal anomalies.
• CTG → foetal wellbeing.
• Amniotic Fluid Index (5cm-25cm) → <5cm: oligohydramnios, >25cm: polyhydramnios.
  • Polyhydramnios: >2-3L of amniotic fluid.

Management Plan

• Oligohydramnios → delivery if at term. If pre-term, then monitor for further abnormalities.
• Polyhydramnios → amnioreduction or COX inhibitors (decreases foetal urine output).

Complications → oligohydramnios: fetal pulmonary hypoplasia.