Judaism does not view sex as unclean, as a necessary humiliation for the purposes of increase.
Sexual life is seen rather as a physical expression of the union between man and woman, as an act of positive significance in itself, and, at the highest level, as a sacrament.
Therefore, even when sexual relations do not lead to birth (when the woman is already pregnant or when, because of age or other reasons, pregnancy is ruled out) it is still considered a mitzvah.
Modesty is not the result of shame concerning sex, but of great respect toward something extremely personal, intimate, and deserving of the greatest sensitivity.
Jewish writings throughout the ages have included general guidance and recommended ways of experiencing sex, but very little in terms of absolute prescriptions that could be considered obligatory.
Mutual agreement concerning the rhythm and form of sexual relations is one of the few standard elements in the literature, as is the need to be considerate of the needs and desires of the woman, even more so than the man.
–Rabbi Adin Steinsaltz
From "Marital Relations" in Teshuvah: A Guide for the Newly Observant Jew by Rabbi Adin Steinsaltz