Final answer:
Magnesium sulfate is used for preterm labor and preeclampsia to relax the uterus and prevent seizures, respectively, and can cause a feeling of being flushed.
Step-by-step explanation:
The patient is instructed to expect a feeling of being flushed after taking Mg sulfate, commonly known as magnesium sulfate. This reaction is for preterm labor and preeclampsia, not for gestational diabetes and placenta previa. Magnesium sulfate is used to relax the uterus in cases of preterm labor to delay birth and give the baby more time to develop. In cases of preeclampsia, it is used to prevent seizures, which is a condition where the expectant mother experiences high blood pressure and other symptoms that can be dangerous for both mother and baby.