amniotic fluid

Amniotic fluid is produced initially via diffusion across fetal skin and maternal/fetal membranes, but by the second trimester, fetal urine becomes the primary source of fluid production, while fetal swallowing and lung fluid absorption remove it. This balance is critical: any disruption in production or removal alters fluid volume. Oligohydramnios (low amniotic fluid) is classically associated with fetal renal abnormalities (e.g., bilateral renal agenesis - Potter sequence), uteroplacental insufficiency, or premature rupture of membranes; it can lead to pulmonary hypoplasia and limb deformities due to compression. Polyhydramnios (excess fluid) is associated with fetal inability to swallow (esophageal or duodenal atresia, anencephaly), maternal diabetes (fetal hyperglycemia causing polyuria), or multiple gestations. Amniotic fluid also serves diagnostic purposes: amniocentesis allows for karyotyping, assessment of lung maturity (lecithin/sphingomyelin ratio), and detection of neural tube defects (elevated alpha-fetoprotein). Amniotic fluid embolism is a rare but life-threatening obstetric emergency where fluid enters maternal circulation, causing sudden cardiovascular collapse, hypoxia, and coagulopathy (DIC), often during labor or delivery. Clinically, amniotic fluid index (AFI) or single deepest pocket (SDP) measurements via ultrasound are used to assess fluid volume and fetal well-being.