Prolactin levels are highest in which of the following?

Prolactin levels in maternal plasma increase markedly during normal pregnancy. Concentrations are usually 10 fold greater at term- about 150 ng/mL compared to non pregnant women. Paradoxically, plasma concentrations drop after delivery even in women who are breast feeding. During lactation, pulsatile bursts of prolactin are a response to suckling. The alveolar cells are the principal sites for production of milk. "Although some secretory activity is evident during pregnancy and accelerated following delivery, milk secretion actually stas on 3rd or 4th postpaum day Probably, steroids -- estrogen and progesterone circulating during pregnancy make the breast tissues unresponsive to prolactin. When the estrogen and progesterone are withdrawn following delivery, prolactin begins its milk secretory activity in previously fully developed mammary glands.