I will add to this- as people in your late 30s, IIRC, make a decision sooner than later for a couple of reasons: the obvious increased chances of problems with the pregnancy plus, it really does get physically harder for the woman to be pregnant. you also never know if you'll need to go the fertility route, which will add further time and expense.
our good friend was married in her mid 30s and both were ambivalent about kids. when they decided to go for it, it became apparent one of them wasn't working. the dude #####-footed around and she ultimately dumped him. fast forward and she and the new guy had to go through a few years of fertility treatments (losing one along the way)... she spent the last four months of her recent pregnancy in her mid 40s on bed-rest. (baby is beautiful and healthy).