Throughout history this has been one of the shapes plus usual for the delivery. There are historical references from countries such as Australia, Turkey, India, Africa, Europe, Mesoamerica and South America. There is an explanation, since it is a position natural in which the woman feels comfortable and benefits the labor.
The vertical position is one in which the trunk of the woman and its pelvic channel oscillate within an angle of 45º and 90º with respect to the horizontal plane, the most common positions are: sitting (in chair or stool obstetric), semidecubitus (trunk inclined backwards 45º with respect to the vertical), kneeling , squatting or standing.
(Source: "Intercultural care of pregnancy, delivery and puerperium in health services.) Vertical position of labor" text of the Undersecretariat of Innovation and Quality, General Directorate of Health Planning and Development, Ministry of Health.