What outcome are you looking at? Length of second stage labour? I haven't seen a study that shows that. And if there is, the effect size won't be huge.
The plain language summary is that exercise and fitness (be sure to check with your healthcare provider before making significant changes in exercise while pregnant) increase the likelihood of healthy pregnancies and babies for all pregnant people. That said, the vast majority 'out of shape' (ie, sedentary, low lean muscle mass, low V02 max?) pregnant people in Canada have healthy pregnancies and babies. I'd rather Mum be out of shape than have poorly controlled diabetes or high blood pressure, lack access to prenatal care, miss prenatal vitamins, etc. It's not that high on the list to be honest and let's not shame