This is something I've often thought about, mainly because of my difficulty in conceiving, but something which dh and I have discussed more recently. His sister is very much career driven, but recently she started talking about starting a family. They are in process of moving house, and initially were going to buy a bigger house so that they could have a family in the not too distant future. NOw her job has changed somewhat and she will have the chance to move abroad in the next 3 years or so, so now they've changed their plans and a family home is no longer on the cards. She will work in canada estabilshing her career for some time, and said that she will think about children then. DH has said so many times "she's going to leave it too late, and then she might regret it if she can't fall pregnant". Sil is very blasay, has the attitude that she pretty much can fall pregnant when she decides the time is right, but we all know that's not always the case? Of course I would never say anything as if/when she starts her family is her business, but I've often thought of saying to her "don't leave it too late, it might not happen when you want it to".
So would you ever casually say to someone to not be too certain they would get pg straight away if they put off having kids?