Three or four kids?

A week or so ago, some of our friends sent us articles based on a recent study that "four kids are easier than three". We'd heard it before, that three is really tough, and it's true. Going from zero to one was very tough, because everything is new, and your whole life changes. One to two was easy, and even easier, because suddenly the world didn't revolve only around one child (which never felt very healthy), and the kids could keep each other company fairly early on. Three has been a physical and organizational shock, because two kids, two hands, two parents works fairly well. With three I've often felt overwhelmed, and also feel like the third is again like a single child, although they play and bond fairly well as a three-some as well, or in different compositions (eldest-youngest, middle-youngest). In that sense, I can imagine that number four pairs up with number three, and things just roll along again. BUT, as I have discussed with several moms of three I know (and their are surprisingly many in my group of friends), we - as women - feel overwhelmed with the idea of another pregnancy (we do not feel physically strong enough anymore, as three was quite a strain on our bodies), feel like life is finally rolling again after the shock of "number 3", and also feel like we're somehow barely managing with our careers, and number 4 would be the end to that. I know that it wouldn't, and I know that we would all manage. And if nature would want it, I would be thrilled in part - a child is simply the biggest gift on earth, and I could never imagine not wanting a new little human being if it is on its way. Several of my friends with 3 are slightly older than I am (instead of mid-30s, end 30-s), so their thoughts are much more acute: it's now or never, because none of them want children later into their 40s. I still have time. We could, in theory, still go from 3 to 6…. Any articles on "six is easier than three"?