What is the best words to say to a relative who’s been trying to conceive since 14years back? :( The beloved couple is almost in their early 40's already.

I had a friend who has been married for 10 years and still no kids of their own even though they have been trying. According to her, it's best not to even bring the topic up because it hurts. The words that you say to the couple lingers longer that you think and my friend often broke down few hours after whoever who asked "when's your turn".