Why Does Every Pregnant Woman Become Insulin Resistant?
It is not an oversimplification to say that every woman has to become insulin resistant during pregnancy because the adaptive response preferentially directs nutrients to the fetus. Genetic factors probably amplify the response in some women. Environmental factors would also amplify the response in some women. The environmental factors could be stress, sleep, nutrition, et cetera. The framework is a great one for the point.
Interestingly, gestational diabetes does not always recur in every pregnancy. The process is not fully understood. Like almost everything in medicine, if a woman has had gestational diabetes before, the woman is more likely to have gestational diabetes again. Not everyone gets gestational diabetes again.