Sforno on Genesis 30:11/ספורנו על בראשית ל׳:י״א

1בא גד, this one came coincidentally, for I had not planned to bring him into the world, seeing that I had stopped giving birth. The reason why the word is spelled as a single word with the letter א missing, is to indicate that the conception and pregnancy was not planned but occurred gratuitously. Her pregnancy had somehow become terminated after it had begun. We find a similar construction of the word בגד in Job 6,15: אחי בגדו כמו נחל, “my comrades are fickle like a wadi.”