How can I get the month-to-date in SQL?

How can I get the month-to-date?( for everytime this query is ran it will need to return the count of cases for only the current month and not any of the previous months.) Please advise.

This is my current query:
SELECT         trunc(sysdate,'mon') current_dt
        ,Count(*) Count
FROM pda_main
WHERE result_d BETWEEN TO_DATE('04/01/2006', 'MM/DD/YYYY')
 AND TO_DATE ('12/31/2006', 'MM/DD/YYYY')
GROUP BY        sysdate

This is the return I receive:(below) but if I change the start date in my where statement for result_d to 3/01/2006, it will give me that months data and the current month but I only want the current's month data.

current_dt  | count
4/1/2006    |   21