I think some people just want a law (a verse?) that makes this whole issue "go away." But in fact, that's what the biblical category of wisdom is all about. "Planning" is a normal part of life, to be done with prayer and faith, Jas.4:15. Indeed, children are God's good gift and we may expect his help for us if he sends them, no matter how "inconvenient" they may seem. He also sees fit to not-give children to some couples who very much would like one of their own, and who might very well make good parents. God does open and close the womb, but that text does not mean that would-be parents should never "try" to conceive, any more than it compels reluctant marrieds to have sx purely in order to attempt progeny. It simply means God is in charge, despite what exactly our private aims may be.
Wisdom for one couple may look very different from another. We should not judge one couple or another, but to their own master they stand or fall. We live by faith, or we live like unbelievers; but married sx life will not typically function as a litmus test of faith.
I feel very free to opine on this matter, as like a poster above I have comparatively lots of children. When this past week I mentioned the size of my family to an acquaintance (who presents as an unbeliever), the reply came back, "Wow. You should get a hobby...." I've lived and pastored long enough to know there is no reason everyone needs to adopt my family as their model or ideal. A husband and a wife should, as partners in the grace of life, aim wisely for what they believe God has equipped them to handle. Then, leave the actual results to God's providence and supervening wisdom.