I actually think Boston is massively unfair to women of childbearing age. Women must deal with all the reasons men that might prevent them from running at Boston - injury, sickness, family obligations - and also pregnancy.
Pregnancy lasts nine months. I would say for an *average* women, it probably takes two years to regain the fitness to qualify for Boston if you are at all marginal after childbirth. Let's say 12 months at an absolute minimum to regain the fitness to COMPLETE Boston. I realize some women who run professionally and some women who are just amazing do it faster ,but that is NOT typical. It took me more than two years after my last pregnancy to get anywhere near pre-pregnancy fitness. Many women suffer injuries that take a LONG time to resolve. Pregnancy is no joke.
Now you can qualify for Boston 2019 between September 2017 and September 2018. Let's say you qualify for Boston in September 2017. You become pregnant in October 2017. Baby is born July 2018. That leaves 10 months to get in shape to complete the race - absolutely not enough time. So, you cannot qualify, become pregnant, and then compete.
So now let's consider the amount of time you must be pregnancy-free to compete in Boston. If you leave qualification until the last minute and qualify in September of 2018, you'll have had to have your baby no later than November of 2016, if you are a runner for whom qualifying presents some level of challenge. (For women who will never be good enough to qualify, or who are so good the qualifying times are not a factor, this discussion is obviously meaningless.) Therefore, in order to complete the race, you'll have to be pregnancy-free for 2.5 years.
Being pregnancy-free for 2.5 years actually means your children are 3.25 years apart. The vast majority of women have their children closer together than that. Let's say your typical woman Boston qualifier (higher than average socioeconomic status) has two kids 2.5 years apart starting at age 28. She's pregnant or recovering from pregnancy from age 27 until 32. No matter what timing she chooses, she loses at least 5 years of opportunity to qualify for Boston.
I would much rather Boston tighten qualifying times for women between 25 and 38 but give women in that age bracket the chance to defer a qualifier by up to three years.
I realize I'm addressing only one age bracket here, but I was mulling this in annoyance this morning as I contemplate another child and the havoc it'll wreak on my ability to run my next marathon.