Biological gestational age and its calendar assessment with ultrasound. Part 1: Physiological considerations

Biological gestational age differs from calendar age, which is only its measurement. In spite of that in many countries all over the world, the rule for termination of pregnancy exclusively because its calendar duration is longer than 293 days (so-called postterm pregnancy) is widely applied. Constant increase in the blood oxytocinase level of pregnant women, just like the sonographic measurements of fetal bodies, proves the appropriate development of pregnancy with all the more accuracy, the more similar the subsequent values of the enzymatic and ultrasonographic determinations. From medical and ethical points of view the 'obstetrical' scale comprising sequential periods' pre-, at- and post-term' is an incorrect way of calculating the duration of pregnancy. Gynecologists have to use the word 'term' only to describe an individual's date of fetal maturity (birth-date) and the possible true pre- and post-term of an individual should be placed within as well as outside the normal range of deliveries.