Testosterone goes down for some women after the delivery, and breast-feeding releases the hormone prolactin, which inhibits arousal.

CNN: New moms and the post-baby sex slump

These hormones include cortisol (which is related to stress), estradiol (the main female sex hormone) and prolactin (which, as its name suggests, triggers her breast tissue to develop the ability to secrete milk).

ECONOMIST: Hormones and fatherhood

The men in these couples, she discovered, exhibited significant changes in their levels of cortisol, testosterone (the principal male sex hormone, and thus in some sense the masculine equivalent of estradiol) and prolactin over the courses of their partners' pregnancies.

ECONOMIST: Hormones and fatherhood