**Core Concept**
The amniotic fluid index (AFI) is a measure used to assess the volume of amniotic fluid in the uterus during pregnancy. It is calculated by measuring the vertical depth of the largest pocket of amniotic fluid in each of the four quadrants of the uterus and then averaging the results. The AFI is an important tool for monitoring fetal well-being and detecting potential complications such as oligohydramnios or polyhydramnios.

**Why the Correct Answer is Right**
The AFI typically reaches its maximum value around 32-34 weeks of gestation and then decreases slightly. This decrease is due to the gradual compression of the fetal lungs and kidneys, which reduces the production of amniotic fluid. After 36 weeks, the AFI may remain relatively stable or even decrease further as the fetus prepares for birth. Therefore, stating that there is a steady increase in AFI after 36 weeks is incorrect.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true. The AFI is indeed calculated by adding the vertical depths of the largest pocket in each of the four equal uterine quadrants.

**Option B:** This statement is true. Fluid restriction, such as in the case of oligohydramnios, may lower the AFI.

**Option C:** This statement is true. Significant hydramnios (polyhydramnios) is defined by an AFI greater than 24 cm.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the AFI is just one tool used to evaluate fetal well-being, and a single measurement should not be used in isolation to make clinical decisions. A combination of clinical evaluation, ultrasound findings, and other diagnostic tests should be considered when assessing fetal health.

**Correct Answer:**
✓ Correct Answer: D. There is steady increase in AFI after 36 weeks