From** Shagnasty’s **list, the most fertile two women who did NOT have any twins had 27 children each. Only one in thirty births are a twin birth, so the women above that count, who mostly got there by having multiple twins, triplets and even quads or quins, are clearly more-than-ordinarily fertile. An ordinarily fertile woman going for 19 kids would generally expect to do so with 0 or 1 twin births. So - 18 or 19 pregnancies, starting from age 20, one a year gets you to age 39, well into the age where fertility is starting to decline … I don’t think it’s realistic. I don’t think the ‘one a year’ schedule is all that realistic even for women at peak fertility, considering that some estimates are that only 30% of fertilised eggs implant, and another 10 or 20 percent of pregnancies end in a miscarriage.
Some people are just particularly fertile.