Question

At what time during gestation does phosphatidyl glycerol appear?

• A. 20 weeks
• B. 28 weeks
• C. 32 weeks
• D. 35 weeks

Hint:

Remember that phosphatidyl glycerol appears later than lecithin in the surfactant timeline.

Answer 1

The Correct Option is D

Step 1: Recall why phospholipids in amniotic fluid matter.
As the fetal lungs mature, they start producing surfactant, a mix of phospholipids that keeps the tiny air sacs from collapsing after birth. These phospholipids leak into the amniotic fluid and can be measured to judge how ready the lungs are for life outside the womb.

Step 2: Recall the timeline of these phospholipids.
Lecithin, the main surfactant phospholipid, starts rising from around 28 weeks and increases steadily, and the lecithin to sphingomyelin ratio is used from that point to judge lung maturity. Phosphatidyl glycerol is a different, later marker. It appears only once the surfactant system is more fully developed, typically from about 35 weeks of gestation onward.

Step 3: Understand why phosphatidyl glycerol is a stronger marker.
Because it appears later and its presence correlates strongly with a mature, stable surfactant system, phosphatidyl glycerol is considered a reliable confirmatory marker of fetal lung maturity, and is especially useful in situations like diabetic pregnancies where the lecithin to sphingomyelin ratio can be misleading.

Step 4: Rule out the earlier time points.
At 20 weeks, the surfactant system has barely started developing, so neither lecithin nor phosphatidyl glycerol is present in useful amounts. At 28 weeks, lecithin begins its rise, but phosphatidyl glycerol has still not appeared. At 32 weeks, lecithin levels are climbing further, but phosphatidyl glycerol is generally still absent or only just starting to appear in some fetuses.

Step 5: Final answer.
Phosphatidyl glycerol reliably appears from about 35 weeks of gestation, later than lecithin.
\[ \boxed{35\ \text{weeks}} \]