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Invoked: Alice convinces Bob to do it until she is impregnated before he departs overseas, "just in case".
Exploited: Bob is the last heir of his old, rich, proud family in Medieval England. His wife Alice convinces him of the need to get her pregnant before he is called to arms, or his wicked cousin thrice removed that hates her, Charlie, will inherit everything and kick her out if Bob is killed. Bob dies, but the plan works out and his and Alice's son inherits everything.
Bob doesn't want to shackle Alice with a child to raise if he is killed, and they use anticonceptives.
Alice doesn't want to have children now, by Bob or any other man.
Implied: Alice, whose only son is about to go to college, often talks about her husband Bob who died in a war fought around the time Bob Jr. was born, but it is unclear if he was born before or after Bob was killed.