From the Guidelines
Polyhydramnios is primarily caused by maternal diabetes mellitus, fetal gastrointestinal obstructions, and certain fetal infections, while oligohydramnios is most commonly caused by placental insufficiency, intrauterine growth restriction, and fetal renal abnormalities. The main causes of polyhydramnios (excess of amniotic fluid) versus oligohydramnios (decreased amniotic fluid) can be understood by examining the underlying pathophysiological mechanisms. Polyhydramnios is often associated with conditions that impair fetal swallowing or increase amniotic fluid production, such as maternal diabetes mellitus, fetal gastrointestinal obstructions (e.g., esophageal or duodenal atresia), and certain fetal infections 1. On the other hand, oligohydramnios is typically caused by conditions that reduce fetal urine production or compromise membrane integrity, including placental insufficiency, intrauterine growth restriction (IUGR), post-term pregnancy, premature rupture of membranes, maternal hypertension, and fetal renal abnormalities (e.g., renal agenesis or urinary tract obstructions) 1.
Key Causes of Polyhydramnios and Oligohydramnios
- Polyhydramnios:
- Maternal diabetes mellitus
- Fetal gastrointestinal obstructions (e.g., esophageal or duodenal atresia)
- Certain fetal infections
- Twin-twin transfusion syndrome
- Oligohydramnios:
- Placental insufficiency
- Intrauterine growth restriction (IUGR)
- Post-term pregnancy
- Premature rupture of membranes
- Maternal hypertension
- Fetal renal abnormalities (e.g., renal agenesis or urinary tract obstructions)
Both polyhydramnios and oligohdramnios can have significant implications for fetal development and delivery outcomes, emphasizing the importance of careful monitoring and management during pregnancy 1. The identification of these conditions can help guide clinical decision-making and improve outcomes for both the mother and the fetus.
From the Research
Causes of Polyhydramnios
- The most common causes of polyhydramnios are fetal abnormalities, maternal diabetes, and twin pregnancies, but are idiopathic in the 60% of cases 2.
- Other causes of polyhydramnios include congenital infection and alloimmunization 3.
- Gestational diabetes is also a common cause of polyhydramnios, and is often associated with fetal macrosomia 4.
- Fetal anomalies with disturbed fetal swallowing of amniotic fluid can also lead to polyhydramnios 4.
Causes of Oligohydramnios
- Most cases of oligohydramnios are due to premature rupture of membranes 2.
- Other causes of oligohdramnios include fetal abnormalities, such as urinary tract malformations, or chromosomopathies and drugs e.g. NSAID's 2.
- Oligohydramnios of mild entities is often associated with preterm birth, fetal growth restriction 2.
Comparison of Polyhydramnios and Oligohydramnios
- Polyhydramnios complicates 1-3% of pregnancies, while oligohydramnios involves 3-5% of pregnancies 2.
- Perinatal mortality has been reported to range between 10-30% in pregnancies complicated by polyhydramnios, while neonatal survival is highly conditioned by pulmonary hyplosia in cases of oligohydramnios 2.
- The risk of preterm birth reaches up to 22% in pregnancies complicated by polyhydramnios 2.