Zig Zagged: Alice, Bertha, and Claire all get pregnant. Claire wants to miscarry, Alice wants a baby, and Bertha is indifferent. Alice and Bertha miscarry, but Claire gives birth to a live baby. Because she is Alice's friend, Claire gives her baby to Alice.
The actress playing Alice is pregnant, but the writers couldn't easily add a baby to the cast. Instead of replacing Alice's actress, they keep her and say her character became pregnant. It is stated that Alice (the character) miscarried after the baby is born in Real Life.
Lampshaded: Alice's friend Bob says, "Good thing you miscarried, Alice. If you had a baby to look after, you couldn't hang out with us."
Invoked: Alice knows that she always miscarries due to her rare condition, but continues to get pregnant anyway, possibly hoping she'll get lucky and give birth to a live baby.
Exploited: Charles the rapist doesn't want to find a Doorstop Baby at his house, so he only rapes women who always miscarry (like Alice) or who are sterile.
Alice refuses to have sex, for fear that she will miscarry again.