When the Torah describes the birth of a male, the passuk refers to it in the past tense: “וילדה” she gave birth.  However, in the laws concerning a female, the word “תלד” (she will give birth) is used in the future tense.  The reason for this could be as follows: the birth of a boy is celebrated with much anticipation, as he brings many opportunities.  The parents will perform the mitzvah of Bris Milah, teach him the Torah, and celebrate a Bar Mitzvah.

Chazal say: “מחשבה טובה הקב”ה מצרפה למעשה” – a good thought, Hashem considers it as if it was done.” Therefore, the mere craving for being able to do these mitzvos counts as if they have already been done.

Thus, by a male it says, “וילדה” in the past tense, as if the boy has already been born.