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Notes: Objectives To establish the relation between fetal abdominal circumference and birthweight in a large population of fetuses; to identify whether the error in estimating birthweight by abdominal circumference varied with the magnitude of abdominal circumference; and to establish whether adding femur length to abdominal circumference caused a clinically important reduction of error in predicting birthweight.Design A retrospective study.Setting The ultrasound department of a teaching maternity hospital offering a tertiary referral service.Sample From 3512 nondiabetic women with a normally formed singleton fetus, an abdominal circumference measurement of the infant was made within seven days of delivery; of these, 1213 had a femur length measurement performed at the same time.Results There was a linear relation between abdominal circumference and birthweight. There was a strong inverse correlation between the proportional error in predicting birthweight from the abdominal circumference and the magnitude of the abdominal circumference. Both the Campbell and Wilkin equation (abdominal circumference alone) and the Hadlock equation (abdominal circumference and femur length) were associated with systematic errors, especially with larger birthweight infants. The median absolute errors for the two equations were not significantly different overall (6.98% and 6.86% respectively), although the Hadlock equation was significantly more accurate in predicting birthweight in infants weighing greater than 4500 g. However, no threshold value of abdominal circumference or of estimated fetal weight using the Hadlock equation had a positive predictive value in estimating infants of 〉 4500 g of greater than 35%.Conclusions Prediction of birthweight should be by abdominal circumference alone. 〈link href="#t1"〉Table 1 presents robust estimates of the error of predicting birthweight using fetal abdominal circumference.〈tabular xml:id="t1"〉1〈title type="main"〉 The relation between fetal abdominal circumference (AC) and birthweight (BW). 〈table colsep="0" rowsep="0" frame="topbot" pgwide="0" orient="port"〉〈tgroup cols="5" align="left"〉〈colspec colnum="1" colname="col1" align="left"/〉〈colspec colnum="2" colname="col2" align="center"/〉〈colspec colnum="3" colname="col3" align="center"/〉〈colspec colnum="4" colname="col4" align="center"/〉〈colspec colnum="5" colname="col5" align="center"/〉〈thead valign="bottom"〉〈row rowsep="1"〉AC (mm)nMedian BW(g)10th-90th centile BW (g)Range BW(g)〈tbody valign="top"〉200-20913900750-1030740-1040210-219201040830-1370780-1400220–229201060750-1410650-1460230-239281255980-1470900-1860240-2493614351200-17901080-1950250-2593715801290-19251180-2260260-2695618351490-21901340-2400270-2798920001640-23201390-2620280-28913422651920-26601530-2910290-29921925302130-29001820-3100300-30935026852340-30802010-3420310-31938728502470-32902110-3650320-32948430602700-34702350-3770330-33943932602880-37002570-3980340-34942333803040-38602670-4240350-35931436153240-40402890-4460360-36924537503330-11903020-4610370-37911738403480-43603180-4790380-3896641403660-46403470-4820390-3993542903665-46753640-5000

Notes: Measurements of fetal cardiac electromechanical intervals were obtained in two groups of patients before and during labour. This was achieved by means of a system, developed in our Department, which allows the simultaneous recording of the fetal electrocardiogram and filtered Doppler signals from the fetal heart. The intervals studied were the pre-ejection period (PEP), the phase of isovolumetric contraction (IVC) and the left ventricular ejection time (LVET). Mean and SD values prior to the onset of labour were established and found to be 73.6±4.7 mseconds, 38.9±5.8 mseconds, and 155.2±9.6 mseconds respectively. While LVET varied inversely with heart rate, PEP and IVC showed no such correlation. In the second part of the study, serial measurements were made throughout labour in 22 patients. Eighteen of these fetuses had normal pH values at or near delivery, and in 16 of them PEP measurements varied by less than 10 mseconds from the pre-labour value, the remaining two fetuses exhibiting an unexplained shortening of this interval. All four fetuses with evidence of acidosis at delivery had PEP measurements which lengthened by more than 10 mseconds during labour. It is suggested that, with further development and experience, this technique may prove to be a useful adjunct to current methods for intrapartum fetal monitoring.

Notes: Summary. Cardiac electromechanical intervals were measured during labour in 103 unselected human fetuses. Mean values (±SD) for the three intervals measured were 76.01±9.93 ms for the pre-ejection period, 41.56±8.51 ms for the isovolumetric contraction time and 156.23±16.58 ms for the left ventricular ejection time. These are consistent with previously reported data from our own and other centres. The intervals studied did not alter significantly as labour proceeded or during uterine contractions. There was no consistent correlation between them and fetal scalp blood P o2,P co2 or pH, although the pre-ejection period was shortened considerably in three very acidaemic or hypoxic fetuses, and it was prolonged in association with tight nuchal cord entanglement and variable decelerations in fetal heart rate. These findings raise the possibility of using recorded cardiac electromechanical intervals to determine the clinical significance of different fetal heart-rate patterns that suggest the possibility of fetal distress.

Notes: In 80 patients, multiple measurements of the fetal biparietal diameter were made during one examination using a real-time scanner equipped with a coded cephalometer. From the sets of data, the means and standard deviations for the group of 80 patients were calculated. In 80 per cent of cases, the individual standard deviations of the results were less than or equal to the estimated standard deviation of the group as a whole. The variability of measurement related to biparietal diameter was least in the range 59 to 83 mm. Comparison of the results obtained with the coded device and others obtained ‘blind’ does not reveal any significant advantage for the coded device.

Notes: In 131 patients a comparison was made between measurements obtained using a real-time scanner and those obtained using a Conventional ‘B’ scanner with an attached ‘coded cephalometry system’: 69 per cent of the readings agreed within ±2 mm and, when the ‘B’ scan reading was considered ‘good’, 90 per cent fell within this range. Between 14 and 28 weeks, gestational age diagnoses using the two methods were within one week of each other in 88 of 89 patients.

Notes: In a study to evaluate the reproducibility and accuracy of the sonar technique of measurement of the in vivo fetal crown-rump length (Robinson, 1973), a series of in vivo and in vitro experiments was performed in which the random and systematic errors inherent in the technique were assessed. The potential sources of random error were those of operator judgement, movement of the fetus and mother, machine sensitivity settings and measurement from the photograph; while the sources of systematic error were those of oscilloscope scale factor, and velocity calibration inaccuracies, and the effect of beam width. The overall effect of the random errors, that is, the reproducibility of the technique, was assessed in an in vivo blind trial in which three independent measurements were made of the fetus. In a series of 30 experiments the average standard deviation of the three readings was found to be 1.2 mm. Evaluation of the systematic errors by in vivo experimentation, on the other hand, showed that the basic sonar measurements were in error by an overestimate of 1 mm for the beam width effect and 3.7 per cent for the scale factor and velocity calibration errors. A weighted non-linear regression analysis of 334 measurements was performed in order to obtain a “curve of best fit” for the period covering 6 to 14 weeks of menstrual age. The values obtained were corrected for the systematic errors and compared with widely quoted anatomical figures. In the second part of this investigation the original data was further analyzed to determine on a statistical basis the accuracy of the technique as a method of estimating maturity. It was shown that such an estimate could be made to within 4.7 days with a 95 per cent probability on the basis of a single measurement, and to within 2.7 days if three independent measurements were made.

Notes: Abstract The paper discusses the technical problems, pitfalls and artefacts that we have encountered during ultrasonic B scan examination. Our experience relates to work carried out over the last three years using the Diasonograph, but most of the comments may also be applied to other machines on the market. A knowledge of these problems is essential if the full diagnostic value is to be obtained from the examination.