@article {pmid8221427,
	title = {Case-control study of prenatal ultrasonography exposure in children with delayed speech},
	journal = {CMAJ},
	volume = {149},
	number = {10},
	year = {1993},
	month = {Nov},
	pages = {1435{\textendash}1440},
	author = {Campbell, J. D. and Elford, R. W. and Brant, R. F.}
}
