Three months is the standard maternity leave in the U.S. Most states will give 12 weeks of family leave, paid or unpaid (often unpaid). A lot of women, especially those in medicine, especially those in medical training, take less. *raises hand*
The reasons women go back to work very early include:
1) Loss of income
2) Fear of missing training/schooling
3) Pressure from peers
4) Fear of loss of job
Some women will cite "boredom" as a reason for going back to work early, but I honestly don't believe that if all the other factors were eliminated, they would make the same choice.
I'm going to go out on a limb and say that three months isn't enough. I'm not the kind of woman who wants to stay home indefinitely, but three months is just way too short. Six months is more like it.
1) Unless you have an amazing support system, you're still a mess at three months. Yes, your baby is supposed to sleep through the night at this point, but did you know that "sleeping through the night" is actually defined as sleeping five hours in a row? And that humans should be getting at least eight hours of sleep per night? So unless you're a dolphin or something, you're waking up at least once per night. You're not even close to functioning at full capacity, likely making lots of mistakes.
2) In all honesty, having done it myself, I feel like three months is too young for a baby to be in daycare. Babies that age need a lot of attention and it's so pathetic how they just lie there and can't really interact on their own. By six months, they're sitting up and almost crawling, so it's not so bad. Plus daycare is a vector for disease that their immature immune systems can't handle as well, so you're guaranteed to get lots of "pick up sick kid" calls, which further decreases your work reliability. Of course, a lot of women opt for a nanny, but that's its own set of problems.
3) The recommendation is to give breastmilk exclusively for the first six months, but that is no easy task to accomplish when you're working full time. It either puts even more strain on your employment or causes you to give up.
4) I personally felt like I wasn't emotionally ready at three months to leave the baby. Maybe that's not a good reason. Or maybe it's the only good reason.
I guess I only came up with four reasons, but I think they're four really good reasons. Unfortunately, the reasons for going back early are even more compelling.