Ultrasonic Measurements of Early Fetal Growth

Leonard Harris Cohen


[From PATIENTS AND METHODS section of thesis]

Patients in their second trimester of pregnancy who were under going hysterotomy for psychiatric reasons were examined at Queen Charlotte's Hospital, London, in order to establish the accuracy of the method and to construct a growth curve for the second trimester of pregnancy. A small group of patients was also examined at Yale-New Haven Hospital. Women not undergoing hysterotomy were also examined. Measurements of biparietal diameters in these cases were used only in the construction of the growth curve, since they could not be used to establish the accuracy of the method. Three ultrasonic caliper readings were taken as described above to assess the reproducibility of the caliper recordings. The technique of external cephalometry was as follows. A pair of steel calipers was passed over the maximum transcoronal diameter of the fetal skull so that the tips of the arms of the calipers were just in con tact with the head without causing indentation. A locking screw on the caliper prevented any alteration in the position of the arms. The distance between the arms of the caliper was measured with an engineering vernier caliper, thus allowing measurements to the nearest tenth of a millimeter. Patients less than 13 weeks pregnant were also examined at Queen Charlotte's Hospital. They were examined by B scan in both longitudinal and transverse planes. Polaroid photographs were taken to document findings. It was necessary in these early pregnancies for the patients to have full bladders. The full bladder served to move the uterus into a position where it could better be reached by ultrasounds. In addition, the full bladder served as an excellent medium for the transmission of ultrasonic waves. A study was also undertaken to substantiate or disprove the statement of Hellman et al. that the head is sometimes round when seen earliest ultrasonically with all diameters being nearly equal. The technique of external cephalometry as described above was used to compare biparietal with occipito- frontal diameters in fetuses from 13 to 20 weeks maturity.