BTW, I wouldn't blame 'sexual liberation' for this. It has more to do with economics than 1970s style liberation movements. Same thing with the SINKs and DINKs (Single Income No Kids and Double Income No Kids) sprouting up all over the developed and fore-front developing worlds. As economies develop, more and more people start making choices between a certain standard of living and kids. For most people it leads to a trade-off between the two, whereby they have fewer kids (say replacement, i.e. 2 kids ....although true replacement statistically speaking is 2.1, but debating the statistical stem of 0.1 kids is not necessary here). In certain places, e.g. Japan and some parts of Europe, birth rates have even falled below replacement. In the US they are still slightly above, but a lot of the growth is due to immigration (France also has a similar trend, whereby for Europe their rates are relatively high, but it is mostly due to immigrants giving birth).
Anyways, it is more of an economic decision more than a 'sexual liberation' decision. Whcih is why some nations in Europe are either mulling over eliminating certain taxes for people who have kids, giving them benefits (e.g. educationa nd healthcare fo the kids), or in a few cases even proposing instilling taxes for those who don't have kids. This really has nothing much to do with birth control pills, or women working instead of staying at home.