The Theory of Evolution and Childbirth?

Well, it doesn't "remain" it has only "become" a "painful, laborously difficult and often deadly process" in recent evolutionary history. Two factors have contributed: our relatively recent change to an upright stance, which places practical limits on the female pelvis structure and birth c size. And our increased skull size. Evolution doesn't produce perfection, it produces what works from inherited old structures. Crudely, the survival and reproductive advantages of intelligence and not walking on your hands, outweighed (and apparently continue to outweigh) the disadvantages.