Daughter in law hasnt given us a son, we are so dissapointed. I'm worried she has fertility problems?

My son (41) got married to a woman i dont approve of. I dont think shes right for my son. He lived at home til he got married 4yrs ago. I built a house for him and his wife about 200yards away, i wanted him to live nearby. My daughter in laws a bit of a city person and i know it caused friction when i built this house for my son as we live out the country. She wanted to live 10km away but i was having none of it. The city is no place for rearing children. THis is the best place for them to live and they can help me as i'm not as fast on my feet as i once was. However, my daughter in law is 38 and although we have two grandkids, i know my son and my husband and me would like a grandson. The girl is 38 so i'm worried at this stage, that shes fertilty issues...how do i raise this? My son ures me they are trying but with her work load i dont see how she has time frankly. She is also up at the crack of dawn and doesnt seem to spend much time wtih my son. She goes away with work alot and doesnt leave enough meals in the freezer for my son or enough socks and underwear laundered so i have to look after that. She has a nanny but they dont do any of my sons washing...ridicolous arrangement. Just cooking and minding the kids, no ones 'looking after' my son. How can i ask her if shes REALLY trying for another kid? she could be taking contraception behind my sons back? and him unaware of it? I've discussed this with my son,but he says shes not, i think hes too trusting of her.