Physiological Changes in Pregnancy
Amniotic fluid is mainly secreted by: (LQ)
a. At 16 weeks of gestation and thereafter, fetal urine is the major source of amniotic fluid, and fluid is "consumed" by means of fetal swallowing and gastrointestinal absorption.
b. Fetal anomalies affecting these organ systems will cause abnormalities of amniotic fluid volume.
c. Fetal causes of polyhydramnios include anencephaly, presumably due to impaired swallowing on a neurologic basis, and gastrointestinal tract obstruction (e.g. esophageal or duodenal atresia).
d. Maternal diabetes is also associated with a high incidence of polyhydramnios.
e. Genitourinary tract anomalies that diminish fetal urine output, such as bilateral renal agenesis or posterior urethral valves lead to oligohydramnios. Other causes of oligohydramnios include IUGR and ruptured membranes.