The Effect of Gravitation on the Presentation and Position of the Fetus

A general theory concerning the prenatal origins of cerebral lateralization in humans.

“…One such early fetal influence is responsible for the asymmetric positioning of the major internal organs and is possibly genetically transmitted (Woods, 1986). In addition, a fetal gravitational gradient may be produced by a differential mass on the left and right sides of the body (Barnum, 1915; Duncan & Veit, cited in J. W. Williams, 1926).…”

Physical Theory as a Basis for Successful Rotation of Fetal Malpositions and Conversion of Fetal Malpresentations

“…Except for the fetal head, the fetal back is the heaviest, densest part of the fetal body (Duncan 1868;Barnum 1915). If the fetal head lies on the desired axis of rotation, it will have no effect on the impetus to rotate.…”

Changing fetal position

“…Physical theories of gravity, buoyancy, and friction have an effect on fetal position during pregnancy and labor 9 . These theories are based on the proposition that the fetal back is the heaviest, densest part of the fetus other than the head 10,11 . The heavy part of the fetus will rotate to an inferior position and the less heavy part will rotate to a superior position due to the forces of gravity and buoyancy; friction from the fetus and the uterine wall will inhibit the action of gravity and buoyancy and therefore inhibit rotation 9 .…”

“…The prone maternal posture is likely to facilitate an anterior fetal position and a supine maternal posture is likely to result in a posterior fetal position. In fact, it has been noted, though not documented, that anterior fetal positions are more common in the evening after mothers have been erect than in the morning when posterior positions are more common because mothers have been supine or sidelying 10 . The posterior position has also been noted as being more common following an examination in the doctor's office 3…”