An evaluation of two equations for predicting fetal weight by ultrasound

Vaginal misoprostol for early second-trimester abortion

OBJECTIVES

To demonstrate the effectiveness and safety of misoprostol without the need of postexpulsion systematic curettage in early second-trimester abortions, i.e. at 13-15 weeks' gestation.

METHODS

A group of 151 women, with gestations from 85 to 105 days, received 800 micrograms of vaginal misoprostol every 25 h for a maximum of three doses, without having postexpulsion systematic preventive curettage performed. Outcome measures included successful abortion (complete abortion without requiring a surgical procedure), side-effects, mean expulsion time and mean time of vaginal bleeding.

RESULTS

Complete abortion occurred in 121/151 subjects (80%; 95% confidence interval, 78-87%). The decrease in hemoglobin was statistically significant (p = 0.0001), but without clinical relevance (11.8 mg/dl (SD, 0.9) before treatment and 11.4 mg/dl (SD, 1.0) afterwards. No statistically significant differences were found between the success rate and any of the women's characteristics. Vaginal bleeding lasted 6 +/- 3 days, spotting 6 +/- 3 days, and total bleeding 12 +/- 5 days (median, 11 days; range, 1-29).

CONCLUSIONS

The acceptable expulsion time in 80% of the cases, the fact that postabortion systematic curettage was not needed, the clinically insignificant hemoglobin loss and the abortion rate obtained, show that misoprostol by vaginal administration may be an alternative for interrupting gestation in the early second trimester of pregnancy.

Elective delivery of infants with macrosomia in diabetic women: reduced shoulder dystocia versus increased cesarean deliveries

OBJECTIVE

We sought to test the hypothesis that elective delivery of infants diagnosed with macrosomia by ultrasonographic studies in diabetic women will significantly reduce the rate of shoulder dystocia without significantly increasing cesarean section rate.

STUDY DESIGN

In a prospective study diabetic women with ultrasonographic estimated fetal weight > or = 4250 gm underwent elective cesarean section; women with estimated fetal weight > or = 90th percentile but < 4250 gm underwent induction of labor. Maternal and neonatal outcomes were analyzed and compared for the periods before and after initiation of the protocol.

RESULTS

A total of 2604 diabetic patients were included in this study. The rate of shoulder dystocia was significantly lower after instituting the protocol (2.4% vs 1.1%, odds ratio 2.2). The cesarean section rate increased significantly between the two periods (21.7% vs 25.1%, p < 0.04). Ultrasonography correctly identified the presence or absence of macrosomia in 87% of patients. Only 10.6% of diabetic patients at term required intervention under the protocol (6.8% labor induction, 3.8% elective cesarean section). The rate of shoulder dystocia was 7.4% in macrosomic infants delivered vaginally.

CONCLUSION

An ultrasonographically estimated weight threshold as an indication for elective delivery in diabetic women reduces the rate of shoulder dystocia without a clinically meaningful increase in cesarean section rate. This practice, in conjunction with an intensified management approach to diabetes, improves the outcome of these high-risk women and their infants.

Placental pathophysiology of the twin oligohydramnios-polyhydramnios sequence and the twin-twin transfusion syndrome

Currently accepted sonographic criteria for antenatal diagnosis of twin-twin transfusion (TTT) syndrome include a monochorionic placenta with same-sex twins, marked growth discordance, and oligohydramnios of the growth-retarded twin with coexistent polyhydramnios of the larger twin. Our previous report of nine women fulfilling these criteria, examined using sequential funipuncture of both fetuses, demonstrated inter-twin blood transfusion in only four cases (44 per cent). It was proposed that traditional sonographic criteria actually describe a heterogeneous group of disorders more appropriately described as the twin oligohydramnios-polydramnios sequence (TOPS). True TTT is a subset of this population, the antenatal diagnosis of which requires specific demonstration of transfusion from one fetus (donor) to the other (recipient). In this report, antenatal placental evaluation has been correlated using duplex pulsed-wave Doppler analysis of arterial blood flow velocity with postpartum gross and histopathologic evaluation of the placenta, with special attention to microvasculature. There was a higher incidence of resistance to blood flow, abnormal umbilical cord insertion, and diminished placental microvasculature associated with oligohydramnic growth-retarded (donor) twins when compared with polyhydramnic (recipient) twins. Based on these observations, it is proposed that TTT and TOPS represent asymmetric placental insufficiency resulting from aberrant placentation.

Sonographic diagnosis of intrauterine growth restriction

Estimation of fetal weight in utero using multiple ultrasonic parameters remains the mainstay in screening for IUGR. The use of various fetal morphometric ratios and/or measurements of other fetal parameters may provide additional useful information. Serial evaluation to assess interval growth may be necessary to clarify the diagnosis. The use of Doppler ultrasound, especially the evaluation of the umbilical artery and middle cerebral artery velocity flow, is an important adjunct for both the diagnosis of IUGR caused by uteroplacental insufficiency and its continued management.

Fetal growth in diabetic pregnancy

In summary, fetal macrosomia occurs in almost one third of diabetic pregnancies regardless of class. Abnormal fetal fat stores lead to difficult labor, dystocia, and birth injury as well as postnatal metabolic transition. The abnormal body fat distribution at birth may destine some of these infants to lifelong obesity. Abnormal fetal growth in diabetic pregnancy appears to occur with any elevations in maternal glucose levels, however modest. Detection of macrosomia is therefore a major goal of diabetic pregnancy management.

The fetal aortic pressure pulse waveform in normal and compromised pregnancy

OBJECTIVE

To study the arterial pressure waveform in the descending thoracic aorta during pregnancy in both normal and compromised fetuses.

DESIGN

The pressure pulsation waveform propagated along the vascular tree, and acting laterally on the arterial wall, produces a corresponding change in the vessel diameter. The distance between diametrically opposite points of the aortic lumen was followed using a phase locked loop echo tracking system coupled to a B-mode ultrasonic imager (central frequency 3.5 MHz).

SETTING

Tertiary referral unit, teaching hospital.

PARTICIPANTS

A cross-sectional study of 80 normal fetuses between 20 and 40 weeks yielded normal data. We studied 58 women with evidence of potential fetal compromise (high umbilical artery systolic: diastolic ratio).

MAIN OUTCOME MEASURES

From the aortic diameter waveform we measured the maximum systolic and minimum diastolic dimension and calculated pulse amplitude. The first derivative of the aortic diameter waveform identified the incisura of aortic and pulmonary valve closure and was used to time the end of ventricular ejection and systole.

RESULTS

In normal pregnancy there was an increase in systolic and diastolic diameter and pulse amplitude with advancing gestation. Ventricular ejection time was constant. In the fetal compromised group the absolute systolic and diastolic diameters were within the normal range, but diastolic diameter per unit fetal weight was increased. There was a decrease in pulse amplitude as a percentage of diastolic diameter and an increase in the diastolic systolic diameter ratio. Fetal outcome was examined in relation to the diastolic systolic diameter ratio. Those with a high ratio (above 90th centile of normal group) exhibited significantly more adverse indices of fetal outcome.

CONCLUSIONS

The fetal aortic pressure pulse waveform was represented by the vessel diameter waveform. In fetal compromise reduced pulse amplitude and increased diastolic to systolic diameter ratio suggest corresponding changes in arterial pressure pulse. We suggest these are the response of the cardiac pump to increased afterload imposed by the high umbilical placental vascular resistance.

Morphometry of fetal growth

Intrauterine growth retardation (IUGR) complicates about 5% of all pregnancies and is responsible for substantial perinatal mortality and morbidity. With ultrasound, it is possible to assess fetal brain growth indirectly by measurement of the biparietal diameter, head circumference and transcerebellar diameter. As liver size is affected most profoundly by IUGR, measurement of the abdominal circumference of the fetus provides the earliest evidence of fetal growth restriction. Placental size, assessed with ultrasound, can also indicate the severity of the condition. Once a fetus is diagnosed as having IUGR, its well-being can be monitored with standard heart-rate testing and ultrasound assessment of fetal behaviour. Doppler analysis of the wave form of the fetal arterial and venous circulation hold the greatest promise for managing pregnancies complicated by IUGR.

The accuracy of intrapartum ultrasonographic fetal weight estimation in diabetic pregnancies

OBJECTIVE

Our purpose was to compare the accuracy of ultrasonographic fetal weight estimation in pregnant diabetic women with that of matched nondiabetic controls.

STUDY DESIGN

We performed a case-control study of pregnant patients who underwent ultrasonographic fetal weight estimation within 3 days of delivery. The study group consisted of pregnant diabetic women and nondiabetic controls matched for maternal body mass index and neonatal birth weight. Fetal weight estimates were calculated with use of Hadlock's and Shepard's formulas. The difference between ultrasonographic fetal weight estimation and actual birth weight (absolute percent error) was analyzed with respect to maternal diabetic status and actual birth weight.

RESULTS

A total of 450 patients were studied (225 patients in each group). The mean (+/- SD) gestational age at delivery was 39.0 +/- 1.5 weeks versus 39.9 +/- 1.7 weeks for the diabetic and nondiabetic patients, respectively. There was no statistically significant difference between the two groups with respect to the mean (+/- SD) time interval between the ultrasonographic examination and delivery (0.9 +/- 1.8 days vs 0.8 +/- 2.1 days) or the mean (+/- SD) absolute percent error (9.0% +/- 7.1% vs 8.4% +/- 6.3%). The mean (+/- SD) absolute percent error of fetal weight estimates among subjects with macrosomic fetuses (birth weight > or = 4500 gm) was significantly greater than that observed in fetuses with birth weights < 4500 gm (12.6% +/- 8.4% vs 8.4% +/- 6.5, p = 0.001). This difference was observed irrespective of maternal diabetic status.

CONCLUSION

When matched for maternal body mass index and birth weight, the accuracy of ultrasonographic fetal weight estimation was similar among diabetic and nondiabetic women. Birth weights > or = 4500 gm rather than maternal diabetes seem to be associated with less accurate ultrasonographic fetal weight estimates.

Fetal renal growth evaluated by prenatal ultrasound examination

OBJECTIVE

To determine reference ranges for normal fetal renal size in a population of pregnant patients at Mayo Clinic Rochester.

DESIGN

Normal fetal kidneys were prospectively analyzed relative to gestational age and to fetal body weight.

MATERIAL AND METHODS

In 100 pregnant women, prenatal ultrasound examinations were performed between 18 and 39 weeks of gestation. Fetal renal length and volume were determined by prenatal ultrasonography and compared with gestational age and estimated fetal body weight. Reference ranges as a function of gestational age were obtained for fetal body weight, renal length, renal volume, renal length/ body weight, and renal volume/body weight. Reference ranges as a function of body weight were determined for renal length and renal volume. Polynomial least-squares regression analysis was used to model each of the growth variables (Y) as a function of either gestational age or body weight (X).

RESULTS

Graphic representation of these relationships are presented. These graphs include the 2.5, 5.0, 95.0, and 97.5 percentiles and the predicted value of Y from the regression equations. Fetal body weight, renal length, and renal volume increased throughout gestation, and the ratio between fetal renal volume and body weight remained constant.

CONCLUSION

These data about normal fetal renal growth relative to gestational age and fetal body weight should help identify fetal abnormalities in renal size or growth patterns.

A comparison of misoprostol with and without laminaria tents for induction of second-trimester abortion

OBJECTIVE

Our purpose was to determine whether intracervical placement of laminaria tents would improve the effectiveness of the prostaglandin analog misoprostol for the elective termination of pregnancies in the second trimester.

STUDY DESIGN

Sixty-eight women between 12 and 22 weeks of gestation with either an intrauterine fetal death (n = 40) or medical or genetic indications for pregnancy termination (n = 30) were randomized to receive 200 micrograms of misoprostol administered vaginally every 12 hours with or without intracervical placement of laminaria concurrently with the first dose of misoprostol.

RESULTS

The rate of abortion 24 hours after initiation of treatment was 69.7% in the 33 women receiving misoprostol alone and 68.6% in the 35 women treated with misoprostol and laminaria. The abortion rates 48 hours after initiation of treatment were 84.8% and 91.4%, respectively, an insignificant difference. The complete abortion rate was also similar between women receiving misoprostol alone (39.3%) and the group receiving misoprostol and laminaria (37.5%). There were no significant differences in the incidence of fever, vomiting, diarrhea, or pain. The mean interval from initiation of treatment to abortion was also similar, 15.7 hours in those receiving misoprostol alone and 17.4 hours in those treated with misoprostol and laminaria. In both groups women who had live fetuses at the start of the procedure had a higher failure rate of abortion and a longer time interval to abortion than women whose fetus was dead.

CONCLUSIONS

Laminaria tents inserted concurrently with the first dose of misoprostol do not significantly improve the abortifacient effect of vaginal misoprostol in the second trimester of pregnancy.

Accuracy of estimated fetal weight below 1,000 g

The Warsof formula is 1 of 3 currently recommended by the Australian Society for Ultrasound in Medicine for the routine estimation of fetal weight. However, this formula was derived using mostly large fetuses, and its accuracy in extremely low birth-weight fetuses is not known. Using this formula, we studied 184 infants delivering within 14 days of an estimated fetal weight (EFW) < 1,000 g. The mean percent error in EFW was 11.7% underestimation, with 80% of infants underestimated and 61% of estimates within 15% error. The percent error was consistent at 9.6% throughout the first 9 days, but increased to 32% after 10 days post scan (p < 0.0001). There was a significant association between the accuracy of EFW and maternal height, but not with placental position, liquor volume or multiple pregnancy. EFW underestimated birth-weight on average by 9.6% during the first week, and this error appeared to be mainly due to the formula. The error in EFW became unacceptable after 9 days and repeating the estimate before 10 days is recommended. A different formula may be more suitable for extremely low birth-weight fetuses.

Receiver-operator characteristic curves for the ultrasonographic prediction of small-for-gestational-age fetuses in low-risk pregnancies

OBJECTIVE

Our purpose was to assess the accuracy of third-trimester ultrasonographic biometry in the diagnosis of small-for-gestational-age fetuses in a low-risk obstetric population.

STUDY DESIGN

A total of 1000 low-risk pregnancies were prospectively examined at 31 weeks' gestation. The diagnostic accuracy of the fetal abdominal circumference and estimated fetal weight according to 24 formulas in the literature were evaluated by the use of receiver-operator characteristic curves.

RESULTS

The incidence of a birth weight <10th percentile was 8.2%. The diagnostic accuracies of abdominal circumference and estimated fetal weight were remarkably similar. None of the 24 formulas performed significantly better than the measurement of the abdominal circumference. At a specificity of 90%, 46% of infants with a birth weight <10th percentile and five of six cases with adverse perinatal outcomes were predicted.

CONCLUSION

In a low-risk obstetric population third-trimester ultrasonographic biometry has limited value in predicting small-for-gestational-age fetuses, and estimation of fetal weight does not carry an advantage over measurement of the abdominal circumference. The optimal cutoff value remains uncertain. However, by accepting a 10% false-positive rate, half of small-for-gestational-age fetuses and most perinatal complications could be recognized.

Fetal medicine in an unselected pregnant population

To determine the proportion of an unselected pregnant population referred to a Fetal Medicine Unit, we undertook an observational time-limited cohort study. Of 530 pregnant women booked for delivery at our hospital and with a local postcode in the local District Health Authority, 81 (15.3%) were referred to the Fetal Medicine Unit at least once. The average number of fetal medicine visits was 1.5, a rate of 22 per 100 pregnancies. The indications for referral were assessed as appropriate for all but 2 cases. In 3 cases (0.6%), major genetic diseases were prevented by termination of pregnancy.

Estimation of Fetal Weight by Ultrasound in Term Pregnancy

The objective of the present study was to determine which of the established methods of estimating fetal weight in term and large fetuses is the most accurate. In a study population of 116 term gestations, an ultrasound examination was performed within 7 days of delivery. Each ultrasound measured abdominal and head circumference, biparietal diameter, and femur length using uniform measurement and scanning method criteria. Five different methods were used to calculate estimated fetal weights. Of the five current formulas used to estimate fetal weight in term and large fetuses, the four-parameter method of Hadlock provided the best estimate. The accuracy of estimating fetal weight by ultrasound in term and large fetuses can be improved by using multiple parameters, which in turn may influence clinical judgment in the timing and management of delivery.

Intrapartum management of multiple gestation

The intrapartum management of multiple gestation continues to challenge the obstetric profession. In general, attempted vaginal delivery is appropriate for vertex-vertex twins. The options of external version, breech delivery, and cesarean delivery are analyzed for vertex-nonvertex twins. Special considerations in the intrapartum management of multiple gestation include monoamniotic twins, conjoined twins, and triplet pregnancies.

Calculation of unconditional and conditional reference intervals for foetal size and growth from longitudinal measurements

Methods for estimating unconditional and conditional reference intervals for foetal size and growth based on longitudinal observations are presented. The methods are based on simple random-effects regression models and involve transforming both the response and the covariate (timepoint). A dataset from a designed longitudinal study of foetal size is analysed in detail as a motivating example.

Comparison of intrauterine hematologic and biochemical values between twin pairs with and without stuck twin syndrome

OBJECTIVE

Our purpose was to compare hematologic and biochemical values in cordocentesis specimens from twin pairs with and without stuck twin syndrome.

STUDY DESIGN

Cordocentesis was performed on 38 twin pairs. Assignment to the stuck twin syndrome group (n = 8) was based on ultrasonographic findings of discordant size and amniotic fluid volume, concordant gender, and a single placenta. A receiver-operator characteristic curve was constructed with the use of intertwin hemoglobin differences. For the stuck twin syndrome group regression analysis of gestational age and intertwin hemoglobin difference was done.

RESULTS

We found significant (p = 0.03) intertwin differences in hemoglobin between the stuck twin syndrome group (mean 5.35 gm/dl, range 0.5 to 15.4 gm/dl) and the comparison group (mean 0.10 gm/dl, range 0.0 to 2.4 gm/dl). A nearly significant relationship between gestational age and intertwin hemoglobin difference was noted in the stuck twin syndrome group. When the hemoglobin difference was > 2.4 gm/dl, all cases had stuck twin syndrome (sensitivity = 50%, specificity = 100%, positive predictive value = 100%, negative predictive value = 91%). In the stuck twin syndrome group there was a trend toward larger intertwin differences in albumin and total protein. Intertwin blood gas values between the groups did not differ, but the average PO2 was lower when the smaller twins of the two groups were compared.

CONCLUSION

An intertwin difference in hemoglobin > 2.4 gm/dl is consistent with stuck twin syndrome. Large intertwin hemoglobin differences and imbalances in albumin and total protein may be seen in stuck twin syndrome.

Selection of appropriate ultrasound methods for the estimation of fetal weight

Many methods for fetal weight estimation have been proposed. Earlier formulae were derived solely by regression analysis but more recently formulae based on physical models have been developed. Some of these formulae are lengthy and difficult to use. The main purpose of this study was to evaluate a concise area based formula developed several years ago against popular and recently published formulae. Data from 388 patients over a 5 year period were collected from clinically required ultrasound scans performed within 10 days of delivery. Four of the seven formulae evaluated proved to be equally accurate over a broad range of birthweights (mean absolute deviations 245-249 g), including the area based formula and a circumference based formula derived from it. On the grounds of the number of terms, the precision of coefficients, the physical meaning and the greater accuracy of individual area measurements compared with those derived from circumference, the area based formula should be the method of choice.

The fetal central venous pressure waveform in normal pregnancy and in umbilical placental insufficiency

OBJECTIVE

Our purpose was to study the fetal central venous pressure waveform recorded noninvasively from the inferior vena cava in normal and complicated pregnancies by means of newly developed equipment to follow the vessel lumen diameter.

STUDY DESIGN

A paired ultrasonic phase-locked loop echo tracking system with a high sampling frequency (3000 Hz) was used to follow the movement (point displacement) of diametrically opposite points of the vessel wall. The lumen was measured as the interval between these points. We studied 70 normal fetuses (20 to 40 weeks) and 54 complicated pregnancies with increased umbilical placental resistance.

RESULTS

The four component waves of the central venous pressure waveform (A, X, V, Y) were identified and measured in the fetal recording. The crests of the A and V waves were of approximately equal height. An increase in the descent of the Y trough was observed with advancing gestation. By means of data from the normal group, the complicated group was divided into three subgroups. In 10 fetuses the waveform was normal. In 31 there was a high pulsatile pattern with deep descent from the A crest to X trough so that the pulsatility of the waveform appeared increased. In 13 this was shallow and the pulsatility appeared reduced. Clinical outcome (nonreactive fetal heart rate, percentile birth weight, days in neonatal intensive care unit) was significantly worse in both these latter two subgroups in comparison with normal and in the low compared with the high-pulsatile group.

CONCLUSIONS

Human fetal central venous pressure waveforms can be simply recorded and represented by the transluminal diameter waveform. In fetal compromise the high pulsatility waveform may result from a reduced ventricular ejection and increased end-diastolic pressure in response to the increase in ventricular afterload caused by the placental vessel obliteration. In the most profoundly compromised fetuses the low pulsatility waveform may indicate depressed myocardial function and output.

Estimation of fetal volume by magnetic resonance imaging and stereology

The current methods to monitor fetal growth in utero are based on ultrasound image measurements which, lacking a proper sampling methodology, may be biased to unknown degrees. The Cavalieri method of stereology guarantees the accurate estimation of the volume of an arbitrary object from a few systematic sections. Non-invasive scanning methods, and magnetic resonance imaging (MRI) in particular, are valuable tools to provide the necessary sections, and therefore offer interesting possibilities for unbiased quantification. This paper describes how to estimate fetal volume in utero with a coefficient of error of less than 5% in less than 5 min, from three or four properly sampled MRI scans. MRI was chosen because it does not use ionizing radiations on the one hand, and it offers a good image quality on the other. The impact of potential sources of bias such as fetal motion, chemical shift and partial voluming artefacts is discussed. The methods are illustrated on four subjects monitored between weeks 28 and 40 of gestation.

Use of the transverse cerebellar diameter/abdominal circumference ratio in pregnancies at risk for intrauterine growth retardation

A prospective study was conducted to evaluate the ability of the transverse cerebellar diameter/abdominal circumference ratio to identify growth-retarded fetuses. Of the cases analyzed, 48 of 87 (55%) were growth retarded by birth weight. The transverse cerebellar diameter/abdominal circumference ratio identified growth retardation with a sensitivity of 71%, specificity of 77%, positive predictive value of 79%, and negative predictive value of 68%. Fourteen growth-retarded fetuses were missed by the ratio; however, 57% of the missed cases were severely growth retarded. The transverse cerebellar diameter/abdominal circumference ratio can be useful for the assessment of fetal growth retardation; however, the ratio may be normal in cases of severe fetal growth retardation.

A comparison of single versus multiple growth ultrasonographic examinations in predicting birth weight

OBJECTIVE

Our purpose was to determine whether two or more ultrasonographic fetal growth assessments provide a superior estimate of birth weight than does a single examination.

STUDY DESIGN

Five hundred and eighty five ultrasonographic procedures were performed in 263 patients, divided into single (n = 249) and multiple (n = 247) examination groups. Ultrasonographically estimated fetal weight percentiles and abdominal circumference percentiles were compared with gestationally corrected birth weight percentiles. After the gestational age range with the fewest errors in birth weight percentile prediction (32 to 36 weeks) was determined, patients with a single examination in this range were assigned to the single examination group. In the group with multiple examinations averaged ultrasonographic percentiles were used to predict birth weight percentile. Mean absolute and percentage errors were compared for predictive accuracy by means of analysis of variance and Student t test.

RESULTS

There was a linear correlation between the estimated fetal weight and abdominal circumference percentiles and the birth weight percentile, (r = 0.72, p < 0.0001). The accuracy of birth weight percentile predictions was similar whether one or multiple examinations were performed in the third trimester. Both the abdominal circumference percentile and estimated fetal weight percentile underpredicted birth weight, although the abdominal circumference percentile errors (1% to 2%) were statistically smaller than those derived from estimated fetal weights percentile (9% to 11%, p < 0.0001). Both abdominal circumference percentile and estimated fetal weights percentile consistently overidentified fetuses < 10th percentile (small for gestational age) and underidentified fetuses > 90th percentile (large for gestational age). However, multiple abdominal circumference percentile measurements resulted in improved predictions for small for gestational age (sensitivity 100%, specificity 88%) and large for gestational age (sensitivity 84%, specificity 100%).

CONCLUSIONS

With either the single or multiple examination approach birth weight percentile estimates were within 10% of the actual birth weight percentile approximately 50% of the time. Multiple ultrasonographic examinations provided little improvement in prediction of birth weight compared with a single observation. Multiple measurements of the abdominal circumference percentile may provide improved accuracy in identifying large for gestational age and small for gestational age fetuses.

Fetal cardiovascular hemodynamics in the presence of complete atrioventricular block

OBJECTIVE

Our purpose was to follow serially the hemodynamic adaptation to a congenital complete heart block in a human fetus.

STUDY DESIGN

Longitudinal and serial M-mode and Doppler echocardiography over a 10-week span were performed on a fetus affected by complete heart block. Ventricular fractional shortening, size, and flow across the atrioventricualr valves and outflow tracts were determined starting at 20 weeks up to the time of delivery. Neonatal Doppler follow-up was performed at 2 days of life after implantation of a temporary pacemaker.

RESULTS

The right and left ventricles were able to adapt to sustained bradycardia by increasing their size. This ventricular dilatation was also associated with an increase in fractional shortening, which was associated with ventricualr free wall hypertrophy. When ventricualr heart rate decreased to 38 beats/min, fractional shortening decreased, this was associated with the rapid onset of ascites and pericardial effusion.

CONCLUSION

In the presence of sustained bradycardia ventricular output can increase, because this fetus was able to increase ventricular size and fractional shortening and wall thickness.

Fetal weight estimation by echo-planar magnetic resonance imaging

Fetal weight was estimated in utero in eleven singleton pregnancies by measurement of fetal volume with echo-planar imaging (EPI), a form of magnetic resonance imaging, and by ultrasound measurements. EPI estimates of fetal volume were closely correlated with actual birthweight (R = 0.97). The median difference (expressed as a percentage of actual birthweight) between actual and EPI-estimated birthweights was 3.0% (range 0.6-9.9); this discrepancy was significantly smaller than that found for ultrasonographic estimates (6.5% [1.7-17.8]; p < 0.01).

The value of Doppler ultrasound in the diagnosis and management of twin-to-twin transfusion syndrome

To evaluate the efficiency of the Doppler examination of umbilical arterial blood flow for the antenatal diagnosis and the monitoring of fetal condition during intrauterine treatment of twin-to-twin transfusion syndrome (TTTS), we studied 33 pairs of twins including 5 TTTS cases. In all cases umbilical arterial blood flow was examined by Doppler ultrasound and pulsatility index (PI) was calculated as umbilical arterial impedance. In twins with TTTS, PI of the recipient was outside the normal range and the difference of PI was greater than +0.5. In discordant twins without TTTS and concordant twins, the PI was within the normal range and the difference of PI ranged from -0.5 to +0.5. In 2 cases these findings were found before the appearance of fetal hydrops. In 2 TTTS cases transmaternal digitalization prevented the development of hydrops in the recipient. The difference of PI decreased with improvement in the fetal condition, and vice versa. Our data suggested that, in cases with TTTS, Doppler examination of umbilical arterial blood flow was effective in predicting fetal hydrops. Doppler was also very useful for monitoring the fetal condition during intrauterine treatment.

Twin-to-twin transfusion syndrome: a subset of the twin oligohydramnios-polyhydramnios sequence

OBJECTIVE

Our purpose was to assess the adequacy of currently accepted criteria for the diagnosis of twin-to-twin transfusion syndrome.

STUDY DESIGN

Between April 1991 and February 1992 nine consecutive women with twin gestations and ultrasonographic findings of marked growth discordance, coexistent oligohydramnios-polyhydramnios, monochorionic placenta, and same sex of the fetus in the second trimester were evaluated. Mean gestational age at diagnosis was 19 weeks 5 days +/- 5 weeks, and mean growth discordance was 34% +/- 9%. Seven women underwent attempted sequential amniocentesis and cordocentesis at 23 weeks 6 days +/- 2 weeks 4 days to obtain amniotic fluid and cord blood from each fetus. Type O negative, leucocyte-poor, washed adult red blood cells were transfused into the small, oligohydramnic twin during cordocentesis; immediately afterward blood from the polyhydramnic twin was tested with the Kleihauer-Betke stain.

RESULTS

The combined procedure was successful in six (86%) of the cases attempted. True twin-to-twin transfusion was confirmed in only four (44%) of those initially identified by ultrasonographic criteria. Hemoglobin difference > 5 g/dl was present in only one of the four cases, and in this case the recipient was anemic.

CONCLUSIONS

Currently accepted criteria are insufficient for the diagnosis of true twin-to-twin transfusion. Ultrasonographic findings of marked growth discordance, coexistent oligohydramnios-polyhydramnios, monochorionic placenta, and same sex identify the twin oligohydramnios-polyhydramnios sequence.

Ultrasonic fetal weight estimation: analysis of inter- and intra-observer variability

Standard ultrasound measurements were performed by two observers in 40 third-trimester fetuses. Observers were blinded to the results of the measurements. Estimated fetal weight (EFW) was calculated using two published formulae. The intra-observer standard deviation for EFW, assessed using one-way analysis of variance, was < 75 g for both observers. The 95% prediction intervals for inter-observer comparisons of EFW, calculated using the limits of agreement method, were -187.3 g to 139.8 g, and -159.9 g to 124.3 g, using the two formulae. The results suggest that measurements of EFW are reproducible. The prediction interval is comparable to the weekly fetal weight increment in normal fetuses.

Ultrasound fetal weight estimation: precision or guess work?

We compared the prediction of birth-weight based on factors shown by epidemiological studies to influence it with the performance of 2 clinical examples of ultrasonic fetal weight estimation reported in the literature. The standardized absolute error of the 2 examples of ultrasonic fetal weight estimation was similar to estimation by multiple regression of birth-weight on maternal age, parity, height and weight in 11,516 Chinese mothers. This severely limits the clinical utility of the estimation derived from these ultrasonic measurements.

The influence of birth order and presentation on intrauterine growth of twins

In order to evaluate the influence of birth order and fetal presentation on antenatal growth of twins we conducted a comparison of prospective measurements of five fetal biometric indices in 50 vertex-vertex and 47 vertex-breech twins. We compared (a) twin A to twin B in both groups; (b) the second and (c) the first twins of both groups. Both groups had similar maternal and neonatal characteristics. The growth curves of the twins were also very similar except for three significant (p < 0.05) deviations: (a) Twin A of the vertex-vertex group, had larger femur length (FL) at 18-19 weeks, abdominal circumference (AC) and estimated fetal weight (EFW) at 29 weeks, and EFW measurements at 36 weeks. (b) Second breech twins, compared to their second vertex cohorts, had significantly smaller biparietal diameter (BPD), head circumference (HC) and FL at 18-19 weeks, BPD and HC at 29 weeks, and EFW at 37 weeks. (c) First twins of the vertex-breech group, as compared to first twins of the vertex-vertex group, had significantly smaller BPD and AC at 18-19 weeks, FL and AC at 21-22 and 29 weeks, FL at 31 weeks, and EFW at 27-28 and 36 weeks' gestation. We concluded that significantly different sonographic fetal indices may be measured at about 20 and 30 weeks' gestation, but not later. An adaptive mechanism attributed to fetal presentation is suggested to explain similar birthweights in spite of these antepartum differences.

Routine ultrasound surveillance of the pregnant uterus

The routine ultrasound examination of the pregnant uterus is presented in this article. The approach is based on published guidelines, dividing the examination into studies of the first trimester and studies of the second and third trimesters. The discussion emphasizes the standard anatomical views and describes the normal sonographic appearances. The methods of obtaining important measurements are described, and tables are provided to analyze these measurements. A systematic approach to obstetric ultrasound is important in ensuring completeness and in maximizing the detection of fetal abnormality.

Twin growth problems: causes and sonographic analysis

Understanding the significant increased risks associated with twin pregnancies requires knowledge of the embryogenesis of twins and the unique placental characteristics seen only in twin gestations. Dizygotic "fraternal" twins, 70% of all twins, are at relatively low risk when compared with monozygotic twins, largely due to abnormalities seen in association with monochorionic placentation. The sonographic determination of chorionicity and amnionicity allows better estimation of pregnancy risk--up to 50% mortality in monochorionic-monoamniotic twins. Careful evaluation of intrauterine twin growth assists in the early identification of fetal abnormalities because normal twin growth should parallel that of singleton pregnancies until late in the third trimester. A number of the unique complications affecting growth in twin pregnancies are discussed, including twin transfusion syndrome, the "stuck twin" phenomenon, twin embolization syndrome, and development of acardiac twins.

Prediction of light-for-gestational age at delivery in twin pregnancies: an evaluation of fetal weight deviation and growth discordance measured by ultrasound

The purpose of this retrospective study was to evaluate and discuss different ultrasound methods widely used, among other things, as predictors for light-for-gestational age (LGA) in twin pregnancies. The methods evaluated and compared as predictors for LGA at birth were: (1) Difference between twins in biparietal diameter; (2) difference in abdominal diameter; (3) the percentage difference in estimated fetal weight between twins; and (4) estimation of the weight deviation from the expected weight during pregnancy. The study comprised 66 twin pregnancies, examined by ultrasound scanning less than 15 days before delivery. Using Relative Operating Characteristic curves (ROC curves) estimated fetal weight deviation was the most sensitive and specific of the methods. It is stressed that fetal discordance is not the appropriate predictor of LGA at birth in twin pregnancies.

Standardized residuals as a means for detection of growth alteration in the pathologic human fetus

This paper introduces and discusses the use of standardized residuals as a technique for comparing the growth of normal and pathologic human fetuses. Anthropometric measures, radiographic measures, and organ weights were regressed on known gestational age of second- and third-trimester fetuses. Standardized residuals were calculated for a group of potentially growth-impaired fetuses. Use of residuals aids in identification of patterns of growth alteration in specific pathologies. Most important, studying the response of developing organ systems to a variety of insults may elucidate mechanisms of growth regulation in the fetus. We emphasize the special quality of the multivariate measures of the core sample of fetuses from the Akron Children's Hospital collection.

Prediction of birthweight by fetal ultrasound biometry

A total of 104 women with singleton pregnancies who were delivered between 37 and 42 weeks gestation had ultrasound scans during the fortnight before delivery. The biparietal diameter (BPD), abdominal circumference (AC) and femur length (FL) were measured in all cases. Estimation of fetal weight (EFW) was done by four different methods: using AC alone, AC/BPD, AC/FL and AC/BPD/FL. Results were compared with values of actual birthweights at delivery. There was no significant difference between the mean birthweights of the 47 boy and 57 girl fetuses studied. The EFW(Shepard) method showed the least bias overall: mean percentage error 1.7%, standard deviation (SD) 10.6%. The other three methods significantly underestimated birthweights on average: EFW(Deter), mean error 2.2%, SD 9.3%, p < 0.02; EFW(Campbell), mean error 5.4%, SD 9.5%, p < 0.001; EFW(Hadlock), mean error 5.6%, SD 9.3%, p < 0.001. The percentage error in each group was significantly negatively correlated (p < 0.001) with the scan-delivery interval. Two new equations were generated which gave more accurate predictions for the cases under study using AC, BPD and FL as a combination and also in addition to scan-delivery interval (SDI) in days.

Transverse cerebellar diameter in twin gestations

OBJECTIVE

The purpose of this study was to evaluate the significance of transverse cerebellar diameter measurements in twin pregnancies.

STUDY DESIGN

A prospective, cross-sectional ultrasonographic study was done on 329 normal singleton fetuses and 47 normal twin pairs. Fetal biometric measurements including biparietal diameter, head circumference, abdominal circumference, femur length, and transverse cerebellar diameter were compared between concordant (n = 13) and discordant (n = 11) twins.

RESULTS

(1) There was no significant difference in transverse cerebellar diameter measurements between normal singleton and twin gestations. (2) There was no significant difference in transverse cerebellar diameter measurements in each twin pair. (3) Transverse cerebellar diameter was unaffected by the chorionicity or discordancy. (4) Predicted gestational age by transverse cerebellar diameter nomogram for singletons provided satisfactory correlation for twins.

CONCLUSION

Transverse cerebellar diameter may be a useful predictor of gestational age and may be independent of discordant growth in twins.

Clinical versus ultrasound estimation of fetal weight

A prospective study was carried out on 50 patients who had their fetal weight estimated by 3 clinicians of different seniority and compared to the ultrasound estimated fetal weights using 3 different formulas. All the patients delivered within 24 hours of their clinical and ultrasound estimates. A wide range of birth-weights (1,800-4,500 g) was estimated among the 3 different races (Malay, Chinese and Indians). The results showed that there was no significant difference in birth-weight estimation amongst the 3 clinicians as well as between the 3 ultrasound formulas used. There was however significant difference between these 2 groups when compared with the actual birthweight with clinical estimation being superior to ultrasound estimation in our population. This level of significance did not extend beyond 4,000 g fetal weight (actual) thus making both clinical and ultrasound estimation of fetal weight equally accurate after 4,000 g. This has important implications for developing countries where there is a lack of technologically advanced ultrasound machines capable of doing sophisticated functions like fetal weight estimations but has experienced clinicians who could perform this function equally well if not better.

Use of the fetal chest in estimating fetal weight

OBJECTIVE

This study was designed to develop formulas using the chest circumference instead of the abdominal circumference for estimating fetal weight.

STUDY DESIGN

Ultrasonographic measurements of the chest circumference, biparietal diameter, abdominal circumference, humeral length, and femoral length were obtained in 75 term fetuses of uncomplicated pregnancies within 24 hours of delivery. Three equations for fetal weight estimation that used the chest circumference, instead of the abdominal circumference, in combination with the biparietal diameter or the humeral length were developed by regression analysis.

RESULTS

The average mean errors of fetal weight estimation for these equations vary from 7.1% to 7.6%.

CONCLUSIONS

These equations may be used in predicting the birth weight when the fetal abdomen is altered by certain fetal abnormalities.

Macrosomia in postdates pregnancies: the accuracy of routine ultrasonographic screening

OBJECTIVE

The purpose of this study was to assess the efficacy of routine ultrasonographic assessment of fetal weight in predicting fetal macrosomia in postdates pregnancies.

STUDY DESIGN

A total of 519 pregnancies of > or = 41 weeks' duration were subjected to ultrasonographic estimation of fetal weight within 1 week of delivery. Estimated fetal weights were compared with birth weights. Linear regression analysis was performed and prediction limits for estimated fetal weights were generated.

RESULTS

Twenty-three percent of infants had birth weights > or = 4000 gm and 4% had birth weights > or = 4500 gm. The mean percent absolute error was 7.7%. At a birth weight of > 3750 gm, the Hadlock model (which uses abdominal circumference and femur length) systematically overestimated the birth weight. The sensitivity, specificity, and positive and negative predictive values for the ultrasonographic diagnosis of macrosomia were 56%, 91%, 64%, and 87%, respectively. The prediction limits generated determine the range of birth weights predicted for a given estimated fetal weight.

CONCLUSION

Routine ultrasonographic screening for macrosomia in postdates pregnancies is associated with a relatively low positive predictive value.

Pregnancy-specific beta 1-glycoprotein (SP1) and its relation to fetal birth weight at term pregnancy

The relation between serum levels of pregnancy-specific beta 1-glycoprotein (SP1) and actual fetal and placental weights was studied in 100 full-term pregnant women. This was compared with fetal weight determination by ultrasound. SP1 levels significantly correlated with fetal and placental weights. Its determination was found to be comparable to ultrasonography in placental fetal weight assessment, especially at the extremes of fetal weight (macrosomia and small for gestational age) where special obstetric management is warranted.

Sonographic estimation of fetal weight in diabetic pregnancy

OBJECTIVE

To investigate whether fetal weight estimation by ultrasound in diabetic pregnancy might be based upon fetal abdominal circumference (AC) alone.

DESIGN

A retrospective study.

SETTING

Diabetes Center, Rigshospitalet and Ultrasound Laboratory, Glostrup Hospital, Copenhagen.

SUBJECTS

Eighty-six diabetic pregnant women who had an ultrasound study within 2 days before delivery.

RESULTS

We assessed in 73 fetuses various formulas based upon biparietal diameter and AC against formulas based upon AC alone, and these were only marginally less effective than the more complex ones. In 86 fetuses an AC was available. These fetuses were divided into a study population and a test population. The linear model was customized for the study population. Evaluation on the test population showed that the relative error (error as a percentage of birthweight) in predicting birthweight had a standard deviation of 7.8%. The efficacy of AC in detecting fetuses greater than 4000 g was examined in the test population: If AC greater than 36.0 cm was chosen as criterion for macrosomia the positive and negative predictive values were 80% (8/10) and 91% (30/33), respectively.

CONCLUSION

Formulas for estimating fetal weight in diabetic pregnancy based on AC alone are almost as effective as more complex ones. We recommend a simple linear formula of fetal weight as a function of AC.

The use of a neural network for the ultrasonographic estimation of fetal weight in the macrosomic fetus

The error associated with regression analysis methods for the ultrasonographic estimation of fetal weight in the suspected macrosomic fetus, approximately 10%, is clinically unacceptable. This study was undertaken to evaluate the applicability of an emerging technique, biologically simulated intelligence, to this problem. One hundred patients with suspected macrosomic fetuses underwent ultrasonographic measurements of biparietal diameter, head and abdominal circumference, femur length, abdominal subcutaneous tissue, and amniotic fluid index. The biologically simulated intelligence model included gestational age, fundal height, age, gravidity, and height. The model was then compared with results obtained from previously published formulas relying on the abdominal circumference and femur length. The biologically simulated intelligence yielded an average error of 4.7% from actual birth weight, statistically better (p = 0.001) than the results obtained from regression models.

Efficacy of the fetal-pelvic index in nulliparous women at high risk for fetal-pelvic disproportion

OBJECTIVE

The null hypothesis of this study is that the fetal-pelvic index will not determine the presence or absence of fetal-pelvic disproportion in 137 nulliparous women at high risk for fetal-pelvic disproportion.

STUDY DESIGN

This study was undertaken by comparing the blinded fetal-pelvic index values and two other methods of identifying fetal-pelvic disproportion, ultrasonography-derived estimated fetal weight greater than or equal to 4000 gm and Mengert's index, to delivery outcomes in 137 nulliparous women at high risk for fetal-pelvic disproportion.

RESULTS

After adequate labor trials, 55 of 73 patients who required operative intervention had a positive fetal-pelvic index (sensitivity = 75%). Seventeen of the 18 patients with a false-negative fetal-pelvic index value had persistent malpositions (15 occipitoposterior, 1 occipitotransverse, and 1 face presentation). Spontaneous vaginal deliveries occurred in 64 patients with 62 of them having a negative fetal-pelvic index (specificity 97%). The overall predictability of the fetal-pelvic index in this patient population was 85% and the positive predictability was 96%. However, neither ultrasonography-derived estimated fetal weight nor x-ray pelvimetry, when used alone, accurately detected the presence or absence of fetal-pelvic disproportion in nulliparous women at high risk for the condition.

CONCLUSION

The fetal-pelvic index is efficacious in determining the presence or absence of fetal-pelvic disproportion in nulliparous women at high risk for the condition.