Heart frequency of the fetus at birth.
Heart frequency was recorded in 10 infants during the delivery and the following day. It was found that during vaginal birth, in cephalic presentation, heart frequency decreased during the last 3 minutes before delivery of the head. In breech presentation the initial deceleration was shorter, while with cesarean section there was no initial deceleration. Shortly after delivery of the head and in close connection with the first cry, a tachycardia lasting approx. 10 minutes was observed in all infants. On the day after birth, all infants had a normal heart frequency. It is concluded that the heart frequency changes correspond to the alterations expected on the basis of the caput compression and the relative fetal hypovolemia arising during the final stage of the vaginal delivery. These observations also indicate that the variable deceleration is caused partly by fetal hypovolemia. The neonatal tachycardia is presumably a response to the ordinary placental transfusion and neonatal adaptation to extra-uterine life.