Which one of the following hormones is not active during pregnancy?

The correct answer is Option (3) → Luteinising hormone

During pregnancy the placenta makes several hormones, and the levels of some others rise in the mother’s blood. These hormones support the growth of the foetus and keep the pregnancy going.

(1) Human chorionic gonadotropin — Active during pregnancy. hCG is made by the placenta, and only in pregnancy.

(2) Human placental lactogen — Active during pregnancy. hPL is also made only in pregnancy.

(3) Luteinising hormone — Not active during pregnancy. It is not among the hormones that NCERT lists for pregnancy. Its mid-cycle surge brings about ovulation, and no ovulation takes place in pregnancy.

(4) Estrogens — Active during pregnancy. Their levels rise several times in the mother’s blood.

NCERT Extract:
Pregnancy and Embryonic Development – “… Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens, etc. In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary. Let us remember that hCG, hPL and relaxin are produced in women only during pregnancy.”
Pregnancy and Embryonic Development – “… In addition, during pregnancy the levels of other hormones like estrogens, progestogens, cortisol, prolactin, thyroxine, etc., are increased several-folds in the maternal blood.”