The correct answer is choice A. Increased progesterone levels are primarily responsible for fatigue and mood swings during pregnancy. Progesterone is a hormone that relaxes the muscles and causes sleepiness and tearfulness.

Choice B is wrong because estrogen levels actually increase during pregnancy, especially in the first 12 weeks.

Estrogen is associated with serotonin, a brain chemical that regulates mood. Changes in estrogen levels can cause anxiety and irritability.

Choice C is wrong because thyroid hormone levels usually decrease during pregnancy, not increase. Low thyroid hormone levels can cause symptoms such as weight gain, constipation, and cold intolerance.

Choice D is wrong because insulin resistance usually occurs later in pregnancy, not early on. Insulin resistance can cause high blood sugar levels and increase the risk of gestational diabetes.

Normal ranges for pregnancy hormones vary depending on the stage of pregnancy and the laboratory methods used.

However, some general ranges are:

• Progesterone: 9 to 47 ng/mL in the first trimester, 17 to 147 ng/mL in the second trimester, and 55 to 200 ng/mL in the third trimester

• Estrogen: 15 to 60 pg/mL in the first trimester, 150 to 1,300 pg/mL in the second trimester, and 1,500 to 6,000 pg/mL in the third trimester

• Thyroid stimulating hormone (TSH): 0.1 to 2.5 mIU/L in the first trimester, 0.2 to 3.0 mIU/L in the second trimester, and 0.3 to 3.0 mIU/L in the third trimester

• Insulin: less than 25 mIU/mL before meals and less than 120 mIU/mL one hour after meals