to complain about, right? come on. >> reporter: her good life isn't just good luck. she made smart decisions. this is mary claire about 15 years ago. she gave birth to her son when she was 33. turns out that's the ideal age for most women. researchers working with "usa today" found women who gave birth to their children between 27 and 36 are the happiest. >> one of the things that happens is so many bright achieving young women, you know, burn out by working like crazy through their 30s. and then try to fit in the childbearing in the late 30s and early 40s. then where are you in mid life? >> you're exhausted. mary claire was. about 15 years ago, she realized she was gaining weight and didn't have energy to cook most nights. so her husband stepped in.