Allow me to add a corollary question. Suppose one spouse decides unilaterally to get a tubal ligation or a vasectomy. In Catholic teaching, would the other spouse then be required to abstain?
I have no idea. I guess it would depend on the age of those involved. The marriage ceremony does include a vow to be open to the possibility of children. This vow would be a lie in this case. For those beyond chiild bearing years this vow is not taken, for obvious reasons. I guess I really don't know.
(Someone mark the date, SoothingDave was stumped.)
SD