How to extract the subdomain from a URL in C# using regular expressions

I recently read a post with some C# code for extracting a subdomain from a URL at Mads Kristensen's blog. Since I am currently working on something where I needed to do the same I decided to share the method I came up with using a regular expression. Here it is for my own and others reference.

private static string GetSubDomain(Uri uri)

{

  string host = uri.Host;

  string subdomain = null;

  if (uri.HostNameType == UriHostNameType.Dns)

  {

    subdomain = Regex.Replace(host, "((.*)(\\..*){2})|(.*)", "$2");

  }

  return subdomain;

}

An item to note with this is if your are looking for better performance I'd suggest creating a static Regex member variable instead of using the static Replace method as I am here.