Probability of breech presentation and its significance.

Existing data related to the probability of breech presentation suggest that the breech presentation is a consequence of mere filling of the intrauterine space, with the same probability of breech and cephalic presentation. As a consequence, group of cephalic presenting fetuses is heterogeneous. Some fetuses randomly assume the cephalic presentation while others assume cephalic presentation 'intentionally' for a reason. Before comparing breech and cephalic presenting fetuses/newborns, bias should be eliminated by subtracting from the cephalic-presenting group the number of fetuses/newborns that is identical with the number of breech-presenting fetuses/newborns with identical characteristics. The subtracted group should be added to the breech-presenting group before comparison with the remaining cephalic-presenting fetuses/newborns. The comparison should be corrected for the gestational age and according to data that are not influenced by delivery. Data suggest that the physiological process that accounts for 92% of cephalic-presenting human fetuses at delivery should be sought from the 25th gestational week onwards.