Tosefta su Salmi 116:6

Three women may engage in relations using a [contraceptive] resorbant (see Ket. 39a:1, Steinsaltz tr.) -- a minor, a pregnant woman, and a nursing woman. A minor, lest she become pregnant and die. What is a "minor"? One who is from eleven years and one day old to twelve years old and one day. Less than that, or more [than that], she may engage in relations in her usual way, and there is no need to be concerned. A pregnant woman, lest her fetus becomes a sandal (i.e., it is flattened due to lack of space in her womb given the existing pregnancy, see Yeb. 100b:17). A nursing woman, lest she kill her son [by having her milk stop up]. And so too Rabbi Meir would say, one should not penetrate [his wife] inside and ejaculate outside, and the Sages say, he may engage in relations in his usual way, and from the Heavens they (i.e., the angels) stand guard over him, as it is said (Ps. 116:6), "God protects the simple ones."