Underwriter,
There is a difference between insurance acceptability and regulations.
For commercial pilots flying airliners there are periods in which they can, from a regulatory point of view, fly.
However most airlines will ground pregnant pilots as soon as the pregnancy is declared. The EU directives on cosmic radiation stipulate that the least achievable exposure should be strived for; that means no flying.
(BTW no evidence that exposure on flights leads to birth or baby problems but as the cosmic radiation is in principle a stochastic risk they decide to interpret it that way)
From a regulatory point of view people can start flying again 4 weeks post partum, providing no complications etc etc.