father of twins (10 Y/O) via medical help here. 10 years ago our doctor said, "30 years ago the natural rate of twins was 3 sets per 1000 births. Now it's 3 sets per 100 births". After a quick search I couldn't find any data supporting a 10x increase in twins over the past 40 years but plenty of articles showing something closer to a 2x increase in the rate of twin births. I suspect the rate of twins amongst our peer group is skewed though since we're upper middle class surrounded by similar peers who can all afford fertility treatments so it appears that there are way more twins then ever...