Is the drop in teen-age pregnancy attributable to education or is it the decreased fertility of boys?
Pesticides with estrogen-like effects have the strongest evidence for sperm reduction.
Liza Mundy writes in Sperm counts and teen pregnancy rates
The great sperm-count debate began in 1992, when a group of Danish scientist published a study suggesting that sperm counts declined globally by about 1 percent a year between 1938 and 1990. This study postulated that "environmental influences," particularly widely used chemical compounds with an impact like that of the female hormone estrogen, might be contributing to a drop in fertility among males. If true, this was obviously an alarming development, particularly given that human sperm counts are already strikingly low compared to almost any other species. "Humans have the worst sperm except for gorillas and ganders of any animal on the planet,"
At a conference at Stanford
the evidence presented are several trends that seem to point to a subtle feminization of male babies: a worldwide rise in hypospadias, a birth defect in which the urethral opening is located on the shaft of the penis rather than at the tip; a rise in cryptorchidism, or undescended testicles; and experiments Swan has done showing that in male babies with high exposure to compounds called phthalates, something called the anogenital distance is decreasing. If you measure the distance from a baby's anus to the genitals, the distance in these males is shorter, more like that of … girls.