I don't think 4 weeks would be doable for me, but if I remember correctly, a lot of women in the US have to go back after 6 weeks. While in school, one of the professors had a baby and could either: a) take a total of 6 weeks off or b) do 3 months part time before returning full time. This was a woman.. I'm sure the same went for the men, but those that had kids returned right away.
Actually, there were three of us in my class that had kids all in the same year. I was going to take a year off, but ended up dropping out to move here (although I can return anytime and have my research here, so I could be doing it..). Another classmate (guy) worked it out with his wife so that they both could work. He did his research while she watched the baby and he watched the baby while she worked as a primary school teacher. He could bring the baby into the lab- at least until he started walking! And...
the third (girl) did I don't know what for a year or so. Then she decided that watching the baby was too much of a responsibility and affecting her work, so she had her mother look after the baby. In Korea. While she remained a student at the Univ of Chicago. The thing is, we were all done with our classes and simply doing our research for our dissertations. There were no set hours or times we had to be in-- especially for me and the other woman who were theorists. All we needed was a computer modem, some paper and pencils (in my case, lots of erasers) and we were set.
Can you imagine? She visited maybe twice a year.
And another thing about returning to work after 6 weeks in the US. The childcare here is amazing-- it's so much better than over there. At least, that's what I've found. Maybe if you had tons of money, it might be the same.. although I doubt that, too. So women have to return to work earlier and put their kids into worse childcare. Maybe that's why it seems a lot more women stay home or work part time there.