Apparently you (and everyone else) will never know until she says so. In the latest interview with USA Today, Jessica Alba said that she will not reveal the sex of the baby to the general public. While close family members will know the truth, Jessica will keep her cards (or her ultrasound) close.
When asked how her daughter Honor feels about being a big sister, she tells USA Today, “She loves babies, she loves her dollies and she likes taking care of her dollies. I think that’s the closest association she can really have with a baby.” I guess the little one is ready to be an older sibling.. the only question now is if Jessica will tell her if she’ll have a baby brother or sister.