Question

The following are causes of oligohydramnios EXCEPT?

• A. IUGR
• B. Postmaturity
• C. Maternal dehydration
• D. Labetolol

Hint:

Think which antihypertensive is safe in pregnancy versus ACE inhibitors and NSAIDs that drop fetal urine.

Answer 1

The Correct Option is D

Step 1: Oligohydramnios means a reduced volume of amniotic fluid (amniotic fluid index below 5 cm or a single deepest pocket below 2 cm). The fluid late in pregnancy is largely fetal urine, so anything that lowers fetal urine output or causes loss of fluid leads to oligohydramnios.

Step 2: IUGR (intrauterine growth restriction) is associated with placental insufficiency. Reduced placental perfusion shunts fetal blood away from the kidneys, lowering urine production and causing oligohydramnios.

Step 3: In postmaturity (post-term pregnancy) placental function declines and amniotic fluid falls progressively, so it is a classic cause. Maternal dehydration reduces maternal plasma volume and is a recognised, reversible cause of low fluid.

Step 4: Labetalol is a combined alpha and beta blocker used to treat hypertension in pregnancy. It is NOT a cause of oligohydramnios. The drugs that classically cause oligohydramnios are ACE inhibitors, ARBs and prostaglandin synthase inhibitors (NSAIDs like indomethacin), which reduce fetal renal output. Hence Labetalol is the exception.