Polyhydramnios and bone development: an unexplored relationship.

Immersion of a humans and Macaca mulatta into a pool with fluid whose specific weight is equal to their specific weight cause bone demineralization. Also, in professional scuba divers, bone mineral density is reduced. Because of water immersion, the apparent weight of scuba divers represents 10% of their actual weight. The aim of this paper was to point out a previously unexplored aspect of fetal bone development in an environment lacking adequate mechanical stress on fetal bone, such as polyhydramnios. In the first part of gestation, the human fetus develops under conditions similar to neutral floating and has an apparent weight which is approximately 5% of its actual weight. During the last trimester of gestation, the fetus overgrows the intrauterine cavity and its apparent body weight is 60-80% of its actual weight. Polyhydramnios represents an excess of amniotic fluid in the uterus during gestation and it can reduce the apparent weight of the fetus to 10-20% of its actual weight. Reduction of the mechanical stress on fetal bone caused by polyhydramnios may significantly affect bone development and ossification during the last trimester of gestation. It is necessary to direct further studies towards examining bone development and mineralization in newborns from gestations complicated by polyhydramnios. A complete lack of data and studies on fetal bone development and bone mineralization in pregnancies complicated by polyhydramnios is not surprising. There is still a misleading opinion that the fetus is in weightlessness condition in the intrauterine environment throughout the second half of gestation regardless of the amount of amniotic fluid.

Possible explanation of cephalic and noncephalic presentation during pregnancy: a theoretical approach.

This paper is based on fact that the fetus is exposed to gravity. The hypothesis is that from the 24th week of gestation an increasing percentage of fetuses occupies an exclusively cephalic presentation, since it allows an uncompromised posture in the caudal direction of body segments whose muscles are first affected by the occurrence and progressive increase of tone. Being in cephalic presentation, in a caudal direction, the fetus relieves body segments of the weight of the hypotonic-atonic part of the body in the cranial direction. In other words, cephalic presentation presents a body axis posture along the line of gravity. When the body axis posture along gravity is absent, the fetus simply fills the intrauterine cavity. In many such cases, the results are transverse lie, breech presentation and also cephalic presentation.