Question:medium
At what time during gestation does phosphatidyl glycerol appear?
At what time during gestation does phosphatidyl glycerol appear?
Show Hint
Remember that phosphatidyl glycerol appears later than lecithin in the surfactant timeline.
Updated On: Jul 8, 2026
- 20 weeks
- 28 weeks
- 32 weeks
- 35 weeks
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: Separate the two surfactant markers.
Fetal lung maturity testing on amniotic fluid looks at two related but different phospholipids. Lecithin rises earlier, from about 28 weeks, and is used in the lecithin to sphingomyelin ratio. Phosphatidyl glycerol is a second, later appearing phospholipid that adds to a mature, stable surfactant film.
Step 2: Place phosphatidyl glycerol on the timeline.
Phosphatidyl glycerol only shows up once the surfactant system has matured further than the early lecithin rise, and this generally happens close to 35 weeks of gestation. Before that point it is essentially undetectable in amniotic fluid.
Step 3: Test the earlier weeks against this.
At 20 weeks the fetal lungs are still forming and produce almost no surfactant phospholipids at all. At 28 weeks lecithin is rising, which is why this is the classic marker, but phosphatidyl glycerol is not yet present. At 32 weeks lecithin continues to rise, yet phosphatidyl glycerol is still typically absent in most pregnancies.
Step 4: Conclude.
Phosphatidyl glycerol becomes detectable later than lecithin, appearing around 35 weeks of gestation.
\[ \boxed{35\ \text{weeks}} \]
Fetal lung maturity testing on amniotic fluid looks at two related but different phospholipids. Lecithin rises earlier, from about 28 weeks, and is used in the lecithin to sphingomyelin ratio. Phosphatidyl glycerol is a second, later appearing phospholipid that adds to a mature, stable surfactant film.
Step 2: Place phosphatidyl glycerol on the timeline.
Phosphatidyl glycerol only shows up once the surfactant system has matured further than the early lecithin rise, and this generally happens close to 35 weeks of gestation. Before that point it is essentially undetectable in amniotic fluid.
Step 3: Test the earlier weeks against this.
At 20 weeks the fetal lungs are still forming and produce almost no surfactant phospholipids at all. At 28 weeks lecithin is rising, which is why this is the classic marker, but phosphatidyl glycerol is not yet present. At 32 weeks lecithin continues to rise, yet phosphatidyl glycerol is still typically absent in most pregnancies.
Step 4: Conclude.
Phosphatidyl glycerol becomes detectable later than lecithin, appearing around 35 weeks of gestation.
\[ \boxed{35\ \text{weeks}} \]
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