This set of posts comes from Pastor Mark Driscoll and his wife Grace. The sermon series The Peasant Princess brought up dozens of questions that they felt they should respond to. The result is this blog series: Christian Sex: Frank Answers to Honest Questions.
Answer: The Old Testament forbids this but the New Testament does not. It is likely a ceremonial aspect of the Old Covenant that is no longer in effect today, though the moral aspect of the Old Covenant is. Therefore, you are allowed to operate with conscience. Some wives don’t mind the mess and just put a towel down, saying they feel more pleasure during this time; other wives find it gross or painful since they are sensitive at this time. So, lovingly arrive at a mutual agreement. If you choose not to, you can find other ways to pleasure each other during this time without completely neglecting your spouse.