This blood test will measure levels of prolactin. Prolactin is a stress hormone that is released by the pituitary gland. High levels of prolactin can prevent the release of FSH and LH. Both of these hormones are responsible for helping your eggs to develop and mature in the ovaries, so that they can be released during ovulation. When you have excess prolactin in your bloodstream, ovulation is not triggered. Prolactin is the hormone that also eventually stimulates the production of breast milk.