RESUMO
The objective of this study was to answer the question whether there is the relation between the uterine capacity, estimated by the total birth weight of fetuses, and the duration of twin gestation. The material for researches contains data received from the books of births and case records concerning the pregnant who gave births to twins in the Institute of Obstetrics and Gynecology of the Medical University in Lódz between 1970-1998. The final analysis concerned only gestations lasting more than 29 weeks, without any complications (excluding prematurity and the growth-discordant twins), and when gestational age was exactly known. The selected group was finally composed of 188 pairs of twins. The analyses considered relations between total birth weight of twins, the sex of newborn babies, parity, and the duration of gestation. The duration of the analyzed twin pregnancies was 35.6 weeks, including primiparous with 35.8 weeks, and multiparous--35.1 weeks. In the group of male-male twin pairs the average duration of pregnancy was 35.7 weeks, in unlike-sexed pairs--35.6 weeks, and in female-female pairs--35.5. In the group of the primiparous having male-male twin pairs the average duration of pregnancy was 35.1 weeks, unlike-sexed pairs--36.4 weeks and female female pairs--36.6 weeks, while in the group of multiparous relatively: 36.4, 35.4, 35.0 weeks. The total birth weight of the specific pairs of twins was from 2270 g to 6900 g (average 4794 g), while in 92% < 5500 g. In the primiparous group it was 4908.1 g. and in the multiparous group--4663.1 g. Analyzing the total twins' weight according to the fetal gender and parity it was found that in primiparous with male-male twins--4715.3, unlike-sexed--5271.6 and female-female--4967.5, whereas in multiparous relatively: 4961.5, 4692.6, 4414.0. The shortening of twin pregnancies was caused by the following factors: total body mass achieved by fetuses was > 5500 g, presence of male sex in twin pregnancies (only in primiparous), and also the multiparity.