This leaves nearly 60% of birth defects for which the etiology is unknown but in which environmental exposure might play a role. For every 3,000,000 . births annually, at least 600,000 embryos or fetuses are aborted spontaneously before the 20th week, and some 24,000 fetuses die before birth. Of live births, nearly 8% are premature, and approximately 7% have low birthweight. Another 3–7% possess some type of malformation. Although the overall incidence of infertility remained stable between 1965 and 1982, infertility among.
