Fertility treatments can produce multiple births, which increases the risk that the babies will arrive early.
VOA: special.2009.10.19
The last point I want to make about juggling return assumptions is that problems have more than likely been compounded by administrators moving incrementally out of low interest return investments and upping allocations to equities (with dire consequences over the past 12 years), extending maturities (which increasesrisk), and cozying up to the low end of the investment grade spectrum.