Returning for a moment to the pregnant uterus at term, we find it to be a thin-walled, muscular sac containing the mature fetus, attached by means of the umbilical cord to the placenta and floating in the amniotic fluid, which is contained within a sac formed by the amniotic and chorionic membranes.
The average fetus at term is about 50 centimetres long, weighs about 3250 grams and is curved and folded upon itself into an ovoid mass, occupying the smallest possible space. (Fig. [50].) Its most frequent attitude is with the back arched; the head bent forward, with chin resting upon chest; arms crossed upon chest below chin; thighs flexed upon abdomen and knees bent.
Fig. 51.—Illustrations from the first textbook on obstetrics, Roesslin’s “Rosengarten,” 1513, which gives an amusing impression of early ideas of the position of the fetus in utero.
With a few exceptions the long axis of the fetus is parallel to the long axis of the mother, and most frequently the head is downward. It was formerly believed that the child stood upright in the uterus until toward the end of pregnancy and then somersaulted to the position it occupied immediately before birth. (Fig. [51].) But it is now known that though the fetus may move about and change its position during the early part of pregnancy, it is not likely greatly to alter its relation to the mother’s body during the tenth lunar month.
Fig. 52.—Attitude of fetus in breech presentation.
It seems advisable to define here certain terms which are in common use in discussing patients in labor, and which will be employed in the following pages.
A nullipara (0–para) is a woman who has not had children.
A primigravida is a woman who is pregnant for the first time.