This is obviously real, and timelines/effects differ. How could growth in utero not matter? And how could pregnancy not deplete resources? That depletion can be reduced and managed, but it happens. I would suspect that most women are anemic by third trimester, just to pick an easy one. Even keeping on weight while breastfeeding can be challenging, to look at an even coarser metric. All of this is pretty consistent with the general unlikelihood of getting pregnant within one year or , sometimes, up to 18 months postpartum, amd you'll often see 3 year spacing as an ideal target. Obviously, that spacing requires that you start having kids pretty early or continue pretty late if you want a large family.

Seeking published results about this is hard because, first, social science and therefore observational studies with results that can readily be disputed; and second, this is one of those "shaming mothers" things that gets tabled or not suggested as research in the first place.