United States law on the issue dates to 1790 and specifically confers natural born citizen status on the child of 2 U.S. citizens who happen to be abroad when the child comes.
Interesting point, the law that repealed the 1790 law utterly drops natural born for chillins born to American citizens born abroad.
They are described only as ‘citizens’ no longer as ‘natural born citizens’...
http://rs6.loc.gov/cgi-bin/ampage?collId=llsl&fileName=001/llsl001.db&recNum=538