How to check if a row exist in the database using PDO?

I want to have a condition that will perform some action when the row doesn't exist at all.

$stmt = $conn->prepare('SELECT * FROM table WHERE ID=?');
$stmt->bindParam(1, $_GET['id'], PDO::PARAM_INT);
$stmt->execute();
$row = $stmt->fetch(PDO::FETCH_ASSOC);

Tried if (count($row) == 0) and if($stmt->rowCount() < 0) but none of them works.