Oligohydramnios

Oligohydramnios

Oligohydramnios is when you have too little amniotic fluid. Amniotic fluid is the fluid that surrounds your baby in 

your uterus (womb). 

                  

An adequate volume of amniotic fluid is critical to allow normal fetal movement 
and growth, and to cushion the fetus and umbilical cord. Oligohydramnios may 
inhibit these processes and can lead to fetal deformation, umbilical cord
 compression, and death.

Oligohydramnios is usually associated with one of the following conditions:

• Rupture of amniotic membranes (ROM).
• Congenital absence of functional renal tissue or obstructive uropathy.
  • Conditions that prevent the formation of urine or the entry of urine into the amniotic sac.
  • Fetal urinary tract malformations, including renal agenesis, cystic dysplasia, and ureteral atresia.
• Decreased renal perfusion leading to reduced urine production.
  • As a sequela of hypoxaemia-induced redistribution of fetal cardiac output.
  • In growth-restricted fetuses, chronic hypoxia results in shunting of fetal blood away from the kidneys to more vital organs.
  • Anuria and oliguria lead to oligohydramnios.
• Post-term gestation:
• The cause of decreased amniotic fluid volume (AFV) in post-term pregnancies is unknown.
• The decreased efficiency of placental function has been proposed as a cause, but this has never been confirmed histologically.
• Decreased fetal renal blood flow and decreased fetal urine production have been demonstrated beyond 42 weeks in pregnancies involving oligohydramnios.

Causes

• Fetal causes include:
  
  • Chromosomal factors.
  • Congenital factors.
  • Intrauterine growth restriction (IUGR)
  • Post-term pregnancy.
  • Premature ROM (PROM).
  • Fetal demise.
• Placental causes include:
  • Abruption.
  • Twin-to-twin transfusion syndrome (monochorionic twins).
• Maternal causes include:
  • Maternal dehydration.
  • Uteroplacental insufficiency.
  • Hypertension.
  • Pre-eclampsia.
  • Diabetes (either pre-existing or gestational diabetes).
  • Chronic hypoxia.
• Drug-induced causes include indometacin and angiotensin-converting enzyme (ACE) inhibitors.
• Idiopathic causes are also possible.