libpq and unwanted stderr output

I have some C programs which use libpq and I do not want them to write
output to the screen (unless, of course, I direct them to do so).
When I use libpq I get unwanted messaged dumped to stderr.

Example (stripped of all error-checking, etc.):

#include "/usr/include/pgsql/libpq-fe.h"

int main ()
{
  PGconn *conn;
  PGresult *res;

  conn = PQconnectdb ("dbname=steve");
  res = PQexec (conn, "create table x (a text primary key, b text)");
  PQclear (res);
  PQfinish (conn);
  return 0;
}

With nary a printf in sight, the following is nonetheless written to
stderr:
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index
"x_pkey" for table "x"

These various programs include daemons, backgrounded processes and
user processes (data input and query screens). In all cases these
messages are causing problems. How do I disable this behaviour?

Cheers,
Steve