This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
Also, this is a specific month, so it uses the がつ reading.
My birthday is April ninth.
Since cherry blossoms are in bloom in April, the prince wants to go to Japan.
My girlfriend suffered from so much stress after her parents divorced in April that she started to grow a little bit of a mustache.