Intrauterine growth restriction (IUGR) is associated with numerous pregnancy-related risk factors except:

Choice A reason: Poor maternal weight gain is a risk factor for IUGR, as it indicates inadequate nutrition and fetal growth.

Choice B reason: Premature rupture of membranes is not a risk factor for IUGR, as it does not affect the placental function or blood flow. It is a complication of pregnancy that can lead to infection, preterm labor, or cord prolapse.

Choice C reason: Smoking is a risk factor for IUGR, as it reduces the oxygen and nutrient delivery to the fetus and causes vasoconstriction of the placental vessels.

Choice D reason: Gestational hypertension is a risk factor for IUGR, as it impairs the placental perfusion and causes fetal hypoxia and acidosis.

Choice A reason: A biophysical profile score of 8 is a good indicator of fetal well-being, but it does not measure the fetal lung maturity. It consists of five parameters: fetal breathing movements, fetal movements, fetal tone, amniotic fluid volume, and nonstress test.

Choice B reason: Phosphatidylglycerol (PG) is a phospholipid that is present in the fetal lung surfactant. Its presence indicates that the fetal lungs are mature, while its absence does not rule out the possibility of maturity.

Choice C reason: Lecithin and sphingomyelin are two phospholipids that are found in the fetal lung surfactant. The L/S ratio is the ratio of lecithin to sphingomyelin in the amniotic fluid. A ratio of 2:1 or higher indicates that the fetal lungs are mature and can produce enough surfactant to prevent respiratory distress syndrome.

Choice D reason: A nonstress test is a test that measures the fetal heart rate and its response to fetal movements. A reactive test means that the fetal heart rate increases by at least 15 beats per minute for at least 15 seconds twice in a 20-minute period. This indicates that the fetus is healthy and well-oxygenated, but it does not reflect the fetal lung maturity.