The most common cause of decreased variability in the fetal heart rate (FHR) that lasts 30 minutes or less is:

Choice A reason: This is not the main reason, as the use of contraceptives for an extended time does not necessarily affect the fertility of a woman. Most contraceptives are reversible and do not cause permanent damage to the reproductive system. However, some contraceptives may take longer to wear off than others, and some may have side effects that can interfere with ovulation or implantation.

Choice B reason: This is the main reason, as the aging process can affect the ovaries and the quality and quantity of the eggs. As a woman ages, her ovarian reserve (the number of eggs in the ovaries) declines, and the eggs become more prone to chromosomal abnormalities. This can reduce the chances of conception and increase the risk of miscarriage or birth defects.

Choice C reason: This is not the main reason, as prepregnancy medical attention is not a prerequisite for achieving pregnancy. However, prepregnancy medical attention can be beneficial for a woman who is older than 35 years, as it can help identify and manage any existing or potential health problems that may affect the pregnancy, such as diabetes, hypertension, or thyroid disorders.

Choice D reason: This is not the main reason, as personal risk behaviors are not specific to a woman who is older than 35 years. Personal risk behaviors are factors that can negatively affect the fertility of any woman, regardless of age. Some examples of personal risk behaviors are smoking, drinking, using drugs, having multiple sexual partners, or having sexually transmitted infections.

Choice A reason: Raising the woman's legs is not the best initial response, as it may worsen the dizziness and light-headedness. This is because raising the legs can increase the blood flow to the lower extremities and decrease the blood flow to the brain, which can cause hypotension (low blood pressure) and hypoxia (low oxygen) in the woman and the fetus.

Choice B reason: Having the woman breathe into a paper bag is not the best initial response, as it may not address the underlying cause of the dizziness and light-headedness. This technique is usually used for hyperventilation (rapid breathing), which can cause respiratory alkalosis (high blood pH) and reduce the carbon dioxide levels in the blood. However, the woman may not be hyperventilating, but rather experiencing supine hypotensive syndrome (low blood pressure when lying on the back) due to the pressure of the uterus on the inferior vena cava (a large vein that returns blood to the heart)².

Choice C reason: Turning the woman on her side is the best initial response, as it can relieve the dizziness and light-headedness by improving the blood flow to the brain and the fetus. This is because turning the woman on her side can reduce the pressure of the uterus on the inferior vena cava and increase the cardiac output (the amount of blood pumped by the heart) and the blood pressure. The left lateral position is preferred, as it can also optimize the placental perfusion (the blood flow to the placenta) and the fetal oxygenation.

Choice D reason: Assessing the woman's blood pressure and pulse is an important response, but not the first one. After turning the woman on her side, the nurse should monitor the vital signs and the fetal heart rate to evaluate the condition of the woman and the fetus. The nurse should also check for other signs and symptoms of supine hypotensive syndrome, such as nausea, sweating, and visual disturbances.