“…why pregnancy is being delayed…”
Finance and economy. Women’s financial independence is rising, due to access to education and careers, so that correlates to the the long-term trend in the shift in the distribution from 20–24 to 30–34.
But it is also the economy. All three of the curves for age-groups by largest proportion, as well as for the most financially vulnerable 15–19, show a noticeable step down (spike in the rate) immediately after 2008.
Great article, great points about bad data collection, change in data collection protocols (more on what to do about this in a bit!) and the consequent wrong conclusions and possible bad allocation of resources!