Does surprise me a bit given that many women end up incontinent to some extent after giving birth - most commonly stress leakage from a weak pelvic floor, less commonly more severe damage such as nerve damage or tearing, leading to urge or total incontinence, and being in nappies for months, years or even lifelong as a result. But physical bladder capacity is a different thing, and the stretching etc. that takes place during pregnancy may increase that in many cases.