I still think Tony has a point and I'll extend it to birth control as well. The "boomers" really were the first generation not only with effective birth control, but the disgusting legal availability of abortion. My parents were what I call "true boomers"--dad was born in 46 and mom in 50 so they were plenty old enough and many like then to have children in 69-75(I was born in 1970). Again, how much impact did effective birth control and then abortion in 73 have on the birth rates for that generation coming of age during that time? Surely you should have seen a pretty good birth rate around my year as those first boomers came of age--1970--if things were status quo on the birth control front, but they weren't--women had the pill now. I'm not even debating birth control, but I don't think its impact can be underestimated when talking about birth statistics in the late 60's and early 70's. My mom is a fertile myrtle and she took the pill--had me in 70 and then my brother in 76 nd another brother in 81. Without the pill, I suspect I would have had another 2 or 3 siblings born in the 70's and so would many others and the birth rates would have been much higher in the 70's.
oops, wanted to add that the pill gave couples the power to delay having children--I think many of my parents peers waited until their 30's and even 40's to have children and it is why you start to see the climb in birth rates again in 1990 where not only are older boomers rounding out families and those who delayed it starting, but younger boomers are just starting and even older genxers are starting families too--big overlap on births during 1990.