Christopher Williams, born in London Nov. 21 at 1 lb., 5 ozs., weighed less at birth than any other single-birth baby on record. A Register reader says that Christa Marie Buehler, born June 17, 1999, really holds the record at 1 lb., 3 ozs. (See letters to the editor.) At birth, she was about one and a half inches shorter than the cartoon strip to the right. The lightest twin on record, 13 ozs., was born in Australia in 1993.