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Assessment of amniotic fluid volume: ultrasound compared with MRI
Abstracts being 1491, 221 and 90 cm3, respectively). The fetal brain and liver doubled in size and the combined volumes accounted for 31% of the increase in total fetal volume during this period. There was a strong correlation between the fetal brain volume by MRI and the head circumference by US (r =0.97) and between the MRI liver volume and the abdominal circumference by ultrasound (r =0.88). The fetus was delivered normally at 42 weeks weighting 3892 g. The predicted birthweight at 42 weeks gestation was 4095 g (ultrasound) and 3702 g (MRI). Ultrasound overestimated the weight by 203 g and MRI underestimated the weight by 190 g. Both ultrasound and MRI were able to predict the birthweight with similar accuracy. Whilst ultrasound is a useful clinical tool for monitoring fetuses with IUGR, MRI has the advantage that fetal brain and liver volumes can be determined with known precision and may be used to assess the rate of growth of individual organs. Assessment of amniotic fluid volume: ultrasound compared with MRI Yeung D.T.K.; Chu W.C.W.; Chan Y.L.; Lam W.W.M.; Metreweli C. Diagnostic Radiology and Organ Imaging Department, Prince of Wales Hospital, Shatin, N.T., Hong Kong Objecti6e: To compare the use of MRI and ultrasound in the assessment of amniotic fluid volume in third trimester pregnancies. Background: The assessment of amniotic fluid volume is important as an abnormal volume may reflect fetal, maternal or placental disease states. Ultrasound is the mainstay of technique but it as at best indirect and semiquantitative. Interobserver variation in the measurement of amniotic fluid index is large, especially when amniotic fluid volume is low. MRI as an alternative technique not only allows measurement of amniotic fluid index but it would also open the way of non-invasive direct amniotic fluid volume calculation. Patients and methods: Eight pregnant women at around 36 weeks of gestation referred for MR pelvimetry because of previous Caesarean section were studied. Ultrasound for amniotic fluid assessment was done just prior to MRI examination. The following parameters were measured: (1) amniotic fluid index by ultrasound (AFI-US); (2) amniotic fluid index by MRI (AFI-MRI); (3) amniotic fluid volume (Vol) calculated by summation of consecutive sectional volume of amniotic fluid obtained by area tracing multiplied by sectional thickness. Results: Correlation coefficients:
AFI-US AFI-MRI Vol
AFI-US
AFI-MRI
Vol
— — —
0.45 — —
0.0 0.0 —
S27
Conclusions: There is poor correlation of AFI measured by US or MRI, with direct volume calculation from MRI. The inadequacy of the amniotic fluid index as an assessment of amniotic fluid volume reflects the inherent inaccuracy in predicting a 3-D parameter from a 2-D method of measurement. A reproducible method of assessment of the uterine cervix in the third trimester of pregnancy using transvaginal ultrasound scanning Marsh M.S.; Lazanakis M.; Economides D.L. Royal Free Hospital, London, UK Approximately 5 – 10% of inductions of labour fail, leading to Caesarean section. Digital vaginal examination of the cervix is used to predict induction outcome but this method has high inter-observer variation. Numerous reports indicate it has a poor predictive value. We have studied the reproducibility of a method of assessing physical characteristics of the cervix using transvaginal ultrasound scanning (TVUSS) in pregnant women at or near term. Fourteen healthy pregnant women were recruited and underwent TVUSS on two occasions using a Toshiba TP8700E with a 5 MHz probe. Hard copies of images of the cervix were taken on each occasion. The probe was withdrawn to the introitus between scans. Measurements of the cervical length, diameter and internal and external os width were taken from each set of hard copy images by an observer blinded to the source of images. The mean age of subjects was 32 years (range 19 – 48), mean gestation 39 weeks (range 36 – 42), median gravidity 3 (range 0 – 3) and median parity 0.5 (range 1 – 5). The coefficient of variation (CV) of the difference between measurements from the first and second scans for the cervical length, width and calculated volume (CVC) were 4.5, 6.9 and 7.4%, respectively. The CV of the diameter of the internal os was 10.8% and that of the calculated volume of cervical opening at the internal os (CV10) was 3.4%. CVC was positively related to parity (MANOVA F =24.8, P=0.0006) and negatively related to gestation (F=12.74, P= 0.001) and to CV10 (F =5.98, P = 0.017). We have developed a reproducible method of examining the uterine cervix in the third trimester of pregnancy by TVUSS. It remains to be established whether this method will predict the outcome of induction of labour better than assessment of the cervix by vaginal examination. The placenta does not move, only the reporter changes position Tyrrell S. Hull Maternity Hospital, Hedon Road, Hull East, Yorkshire, UK From a retrospective review of 2000 transabdominal fetal anomaly scans and the records of 4000 deliveries, we demonstrate that a clinical suspicion of major placenta praevia is as accurate in its detection as is the ultrasound scan. We produce this evidence to contend that as the false positive rate for the identification of placenta praevia is 15% there is no clinical value in reporting the placental localisation up to 20 weeks gestation, indeed it may be detrimental to patient care.
AFI-US AFI-MRI Vol
AFI-US
AFI-MRI
Vol
— — —
0.45 — —
0.0 0.0 —
S27
Conclusions: There is poor correlation of AFI measured by US or MRI, with direct volume calculation from MRI. The inadequacy of the amniotic fluid index as an assessment of amniotic fluid volume reflects the inherent inaccuracy in predicting a 3-D parameter from a 2-D method of measurement. A reproducible method of assessment of the uterine cervix in the third trimester of pregnancy using transvaginal ultrasound scanning Marsh M.S.; Lazanakis M.; Economides D.L. Royal Free Hospital, London, UK Approximately 5 – 10% of inductions of labour fail, leading to Caesarean section. Digital vaginal examination of the cervix is used to predict induction outcome but this method has high inter-observer variation. Numerous reports indicate it has a poor predictive value. We have studied the reproducibility of a method of assessing physical characteristics of the cervix using transvaginal ultrasound scanning (TVUSS) in pregnant women at or near term. Fourteen healthy pregnant women were recruited and underwent TVUSS on two occasions using a Toshiba TP8700E with a 5 MHz probe. Hard copies of images of the cervix were taken on each occasion. The probe was withdrawn to the introitus between scans. Measurements of the cervical length, diameter and internal and external os width were taken from each set of hard copy images by an observer blinded to the source of images. The mean age of subjects was 32 years (range 19 – 48), mean gestation 39 weeks (range 36 – 42), median gravidity 3 (range 0 – 3) and median parity 0.5 (range 1 – 5). The coefficient of variation (CV) of the difference between measurements from the first and second scans for the cervical length, width and calculated volume (CVC) were 4.5, 6.9 and 7.4%, respectively. The CV of the diameter of the internal os was 10.8% and that of the calculated volume of cervical opening at the internal os (CV10) was 3.4%. CVC was positively related to parity (MANOVA F =24.8, P=0.0006) and negatively related to gestation (F=12.74, P= 0.001) and to CV10 (F =5.98, P = 0.017). We have developed a reproducible method of examining the uterine cervix in the third trimester of pregnancy by TVUSS. It remains to be established whether this method will predict the outcome of induction of labour better than assessment of the cervix by vaginal examination. The placenta does not move, only the reporter changes position Tyrrell S. Hull Maternity Hospital, Hedon Road, Hull East, Yorkshire, UK From a retrospective review of 2000 transabdominal fetal anomaly scans and the records of 4000 deliveries, we demonstrate that a clinical suspicion of major placenta praevia is as accurate in its detection as is the ultrasound scan. We produce this evidence to contend that as the false positive rate for the identification of placenta praevia is 15% there is no clinical value in reporting the placental localisation up to 20 weeks gestation, indeed it may be detrimental to patient care.