10 - Ultrasonic Assessment of Fetal Activity

Abstract

Modern ultrasound techniques enable dynamic studies of fetal activity in utero to be studied and quantified. Real-time B-mode scanning has become the method of choice for this purpose because of its ease of use and precision. Fetal movements can be visualized as early as in the seventh week of pregnancy and the development of the movement patterns can be followed throughout the pregnancy. Up to 16 types of movements have been described by several research groups. In early pregnancy, the finding of normal fetal movements is a good prognostic sign in cases of threatened abortion. A decrease in the movement incidence or a qualitative change of the movements are associated with poor outcome. In late pregnancy, the mean incidence of general fetal movements has been found on average to be 9 to 18 per cent of observation time. Fetal breathing movements, mainly with typical "see-saw' configurative changes of the fetal trunk, occur episodically: both long-term and short-term periodicity have been revealed. For recognition of the time incidence pattern of fetal movements or breathing, a sufficiently long observation time (80 to 100 minutes) is necessary. The incidence of fetal breathing movements increases with gestational age and breathing movements become more regular in mature fetuses. Fetal motor activity is subject to several external influences: glucose given to the mother causes an increase in the fetal breathing movement incidence; maternal hypercarbia stimulates the fetal breathing movements; alcohol administered to the mother abolishes fetal breathing; maternal smoking changes the time spacing of breathing and increases the fetal breathing rate; and exposure of the fetus to sound causes an increase in the number of movements. Real-time ultrasonography enables detection and recording of several other fetal activities: hiccups, swallowing and changes in the stomach volume, micturition, and fetal eye movements. The latter fetal activity is used together with fetal movements, fetal mouth movements and fetal heart rate for the identification of the fetal behavioural states. Quantification of fetal activity as a clinical test of fetal well-being was expected to give an alarm signal in cases of fetal hypoxia and imminent asphyxia. In general, the predictive value of a negative result (i.e., a finding of normal fetal activity) was high; the predictive value of decreased or abnormal fetal activity was found to be much less predictive of fetal compromise.(ABSTRACT TRUNCATED AT 400 WORDS)