When is it acceptable or not acceptable for a wife to allow pregnancy without her husband's consent?

I have a friend whose wife did not tell him she went off the pill and now they have a second baby. Though not hateful he feels bitter about being sort of hoodwinked. For the past 8 years he had been working non-stop and studying hard in the past 4 and just graduated and even though naturally he could not have done it without his wife’s help he wanted her to wait till he was ready for another kid.