Can married couples have sexual intercourse before Lord's Supper?
Upon what passage do you base this conclusion? What I suspect has happened is that someone is trying to blend Old Testament laws with the Law of Christ. The Law of Moses had requirements about not being unclean when approaching God in worship. Those laws of uncleanness ended with the Law of Moses. "For He Himself is our peace, who has made both one, and has broken down the middle wall of separation, having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity" (Ephesians 2:14-16). See "Why We Don't Follow the Old Testament" for more details.
While we are not under the Old Testament rules for uncleanness, we still can learn the lessons God was teaching the Israelites through those rules. See: "Uncleanness" for more about this subject.
When people blend two different laws, they create rules which God never gave. "Do not add to His words, lest He rebuke you, and you be found a liar" (Proverbs 30:6).