Which analysis of maternal serum may predict chromosomal abnormalities in the fetus?

Choice A reason: Normal weight women should gain 11.5 to 16 kg during pregnancy, according to the Institute of Medicine (IOM) guidelines. This is based on the body mass index (BMI) of 18.5 to 24.9 before pregnancy.

Choice B reason: Underweight women should gain 12.5 to 18 kg during pregnancy, according to the IOM guidelines. This is based on the BMI of less than 18.5 before pregnancy. Underweight women are at risk of having low birth weight infants, so they need to gain more weight to support fetal growth and development.

Choice C reason: Adolescents are encouraged to strive for weight gains at the upper end of the recommended scale, according to the IOM guidelines. This is because adolescents are still growing themselves and need extra nutrients and calories to meet their own needs and those of the fetus.

Choice D reason: In twin gestations, the weight gain recommended for a single fetus pregnancy should not be simply doubled. The IOM guidelines suggest that women with twin gestations should gain 16.5 to 24.5 kg if they have a normal weight before pregnancy, 14 to 22.5 kg if they are overweight, and 11 to 19 kg if they are obese.

Choice E reason: Obese women should gain at least 7 to 11.5 kg during pregnancy, according to the IOM guidelines. This is based on the BMI of 30 or more before pregnancy. Obese women are at risk of having complications such as gestational diabetes, preeclampsia, and cesarean delivery, so they need to limit their weight gain to avoid further complications.

Choice A reason: The NST has no known contraindications, as it is a non-invasive and safe test that does not stimulate uterine contractions or cause fetal distress. It is the most widely used method of antepartum fetal surveillance.

Choice B reason: The NST is not slightly more expensive than the CST, as it requires less time and equipment. The NST usually takes 20 to 40 minutes, while the CST may take up to 2 hours. The NST only needs a fetal monitor, while the CST also needs an intravenous line and oxytocin infusion.

Choice C reason: The NST does not have fewer false-positive results than the CST, as it has a higher rate of nonreactive results that may indicate fetal compromise when there is none. A nonreactive NST is one that does not show at least two accelerations of the fetal heart rate of 15 beats per minute or more lasting 15 seconds or more in a 20-minute period.

Choice D reason: The NST is not more sensitive in detecting fetal compromise than the CST, as it has a lower predictive value for fetal well-being. A reactive NST is one that shows at least two accelerations of the fetal heart rate of 15 beats per minute or more lasting 15 seconds or more in a 20-minute period. However, a reactive NST does not rule out the possibility of fetal hypoxia or acidosis.