53 And now, Venerable Brethren, we shall explain in detail the evils opposed to each of the benefits of matrimony. First consideration is due to the offspring, which many have the boldness to call the disagreeable burden of matrimony and which they say is to be carefully avoided by married people not through virtuous continence (which Christian law permits in matrimony when both parties consent) but by frustrating the marriage act. Some justify this criminal abuse on the ground that they are weary of children and wish to gratify their desires without their consequent burden. Others say that they cannot on the one hand remain continent nor on the other can they have children because of the difficulties whether on the part of the mother or on the part of family circumstances.
Source: Casti Connubii (Vatican.va)