Now this is perfect story structure. Starting off by detailing how the title came to be, then telling the entire story that details that reason, and then finishing off with an explicit reference to the reasons for that title. In between, making every person connect to every other person intentionally and deliberately.
Case in point, our main character - Mia, although you could argue strongly that it's Pearl - is pulled into at least 3 separate situations that reflect upon her as a mother. None of those situations are specifically about herself as a mother, but they all have a deep connection to it. It is true that almost all the situations in the book have some connection to motherhood, but that's selling each of them short. Ng is crafting something massively complex here in terms of plotting, while at the same time touching on a few phenomenally important aspects of what it means to be human - how accidental so much of life is, how important love is to all of it, and how it's an ever-changing, ever-shaping path that is very hard to hold onto firmly.
The one thing I didn't love so much was the undercurrent of "life is tragedy" that ran through it all. The ending isn't specifically tragic - or to be more fair, not comprehensively tragic - but about 3/4 of the way through the book I found myself exhausted by the realization that so much of life tears you down - and builds you back up again, yes, thankfully. That aspect of constant destruction and renewal, though, is both difficult to accept and a strong component of what makes this book so special.