Does secondhand smoke increase the risk of a low birthweight? a baby is considered have low birthweight if he/she weighs less than 5.5 pounds at birth. according to the national center of health statistics, about 7.8% of all babies born in the u. s. are categorized as low birthweight. suspecting that the national percentage is higher than 7.8%, researchers randomly select 1,200 babies whose mothers had extensive exposure to secondhand smoke during pregnancy and find that 10.4% of the sampled babies are categorized as low birth weight. let p be the proportion of all babies in the united states who are categorized