@book{4900,
	author = {Cunningham, F. Gary. and Cunningham, F. Gary.},
	title = {Williams obstetrics },
	publisher = {McGraw-Hill},
	year = {2001},
	address = {New York },
	edition = {21st ed.},
	url = {http://www.loc.gov/catdir/bios/mh042/2001030497.html}
}