Many attempts have been made to categorize sex positions. Untreated gonococcal infections result in miscarriages , preterm births and perinatal deaths. The hand is usually not actually made into a fist, but instead the thumb is placed between the middle and ring fingers. A study by the Kinsey Institute examined the definition of sex based on a random sample of college students from 29 U. Adjustment in the 21st Century. The receiving partner lies on their side. This term may specifically refer to the double penetration of a woman, with one penis in her anus, and the other in her vagina or of a male, with two penises in his anus. The active partner lies on their back while the receiver kneels with their legs at their sides and their genitals on their mouth. It may also be performed simultaneously for example, when one partner performs cunnilingus, while the other partner performs fellatio , or only one partner may perform upon the other; this creates a multitude of variations. Some, in particular HIV and syphilis, can also be passed in other ways, including from mother to child during pregnancy and childbirth , through blood products , and by shared hypodermic needles. The receiving partner straddles them, also keeping their feet on the floor. Positions during pregnancy The goal is to prevent excessive pressure on the belly and to restrict penetration as required by the particular partners. The receiver lies on his back while the partner lies off to the side of their legs. The Kegan Paul Arabia library, vol. Lying While the active partner lies on their back, the receiver assumes the missionary position but adjusted forward. A pillow is placed under her bottom for added comfort. The receiving partner can kneel while straddling the penetrating partner, with the participants facing each other.