Pulmonary artery/aorta ratio in simple screening for fetal outflow tract abnormalities during the second trimester.

OBJECTIVES: Congenital heart disease is associated with high mortality and morbidity rates, being the most life-threatening defect in the first month of postnatal life and accounting for approximately half of all childhood mortality from birth defects. Despite this, the prenatal detection rate for congenital outflow tract anomalies by ultrasound imaging is relatively low. The aim of this study was to establish a nomogram for the pulmonary artery/aorta (PA/AO) ratio measured in the three-vessel view plane. This ratio was investigated as a simple screening tool for congenital cardiac outflow tract abnormalities. METHODS: The study was a prospective evaluation of 966 singleton fetuses at 16-24 weeks of gestation and 46 fetuses with congenital cardiac outflow tract abnormalities. The diameters of the pulmonary artery and aorta were measured in the three-vessel view. The PA/AO ratio was calculated and a nomogram was constructed. The mean and 95% CI for the ratio were defined and the PA/AO ratios of cases with outflow tract abnormalities were plotted against the values for normal fetuses. RESULTS: The gestational age of the normal group ranged from 16 to 24 weeks, with a median of 19 weeks. The pulmonary artery diameter measured between 2.1 and 4.93 mm (mean, 3.3 mm) and the aorta measured between 2.1 and 5.2 mm (mean, 2.93 mm). The mean (SD) PA/AO ratio was 1.16 (0.18) (95% CI, 0.87-1.58; range 0.61-1.86; median, 1.14). For fetuses with outflow tract abnormalities, the median gestation was 19 weeks and 37/43 (86%) had a PA/AO ratio outside the 95% CI. CONCLUSIONS: The PA/AO ratio derived from measurements in the three-vessel view plane can be used as an initial screening tool for outflow tract anomalies and may have a sensitivity of up to 86%, with a 5% false-positive rate.

Fetal growth patterns in fetuses of women with pregestational diabetes mellitus.

OBJECTIVE: To assess the effect of glucose control on the rate of growth of fetuses in women with pregestational diabetes mellitus (Types 1 and 2). METHODS: All pregestational diabetic women booked at Mater Mothers' Hospital, Brisbane, Australia, between 1 January 1994 and 31 December 2002, were included. Pregnancies with congenital fetal anomalies, multiple pregnancies, and pregnancies terminated prior to 20 weeks' gestation were excluded. Dating scans were performed before 14 weeks' gestation and serial scans were performed at 18, 24, 28, 32 and 36 weeks. Fetal parameters, including biparietal diameter, femur length and abdominal circumference, were recorded. The daily growth rates for biparietal diameter, femur length, and fetal abdominal area were calculated and compared with those in a low-risk (non-diabetic) population. The growth rates in fetuses of women with satisfactory diabetic control (HbA1c < 6.5%) and unsatisfactory control (HbA1c > or = 6.5%) in the three trimesters were compared. RESULTS: A total of 174 diabetic pregnancies were included and a total of 997 ultrasound scans were performed. The growth rates for fetuses of mothers with diabetes mellitus were significantly higher than for those in the low-risk population. The z-scores for biparietal diameter, femur length, and fetal abdominal area were 0.18, 0.59 and 1.44, respectively. Fetuses of diabetic mothers with high HbA1c in the first trimester had significantly greater fetal abdominal area growth rate than those with normal HbA1c (fetal abdominal area z-score of 1.7 vs. 0.75, P = 0.009). Although the fetal abdominal area z-scores in fetuses of diabetic mothers with high HbA1c in the second or third trimesters were also higher than those with normal HbA1c levels, the differences did not reach statistical significance. Maternal obesity did not influence the fetal growth rate. CONCLUSION: The rate of growth of fetuses of diabetic mothers differs from that of the normal population. Growth acceleration persists until the late third trimester. Moreover, periconceptional glucose control appears to have a significant effect on accelerated growth of the fetal abdominal area.

Fetal echocardiography: are we getting it right?

OBJECTIVE: To determine the diagnostic accuracy of prenatal fetal echocardiography. METHODS: The study was a retrospective chart review of 190 consecutive patients over a 3-year period from November 1998 to February 2002 of all women referred to the Maternal Fetal Medicine unit, Mater Mothers Hospital, for fetal echocardiography. The prenatal diagnosis was compared with the postnatal diagnosis made by postnatal echocardiography, surgical findings or post-mortem. The accuracy of prenatal diagnosis was described on a predetermined 4-point scale. RESULTS: Of the 89 patients, for whom complete diagnostic follow-up was available, there was complete agreement between the prenatal and postnatal diagnosis in 63 cases, minor discrepancies in 25 cases and major disagreement in 1 case. CONCLUSIONS: In experienced hands, fetal echocardiography is accurate and allows medical staff and patients information in order manage a pregnancy appropriately.

Factors influencing the prenatal detection of structural congenital heart diseases.

OBJECTIVE: To assess the factors influencing the prenatal detection rate of structural congenital heart diseases (CHDs). METHODS: A retrospective study was conducted at a major obstetric hospital in Australia between 1 January 1996 and 30 June 1999. The medical records of all fetuses and infants born with CHD, except those with isolated patent ductus arteriosus or secundum atrial septal defect, were reviewed. Only pregnancies that had prenatal ultrasound scan assessments for morphological surveys were included. The following factors that may influence the detection rate were assessed: complexity of the lesions; experience of the sonographers (performance in tertiary versus non-tertiary institutions); presence of other structural or chromosomal anomalies; and maternal body mass index (BMI). RESULTS: The incidence of structural CHD in this series, excluding cases referred from other hospitals, was 7.0 per 1000 (179/25 529). Of the 179 pregnancies with CHD, 151 had prenatal ultrasound scans and were included in the study. The overall detection rate for CHDs in this series was 40.4%. The detection rate for isolated septal defects was poor (13.7%). The detection rates were significantly higher for complex lesions (54%), for lesions with concomitant septal defects (66.7%), and for lesions with abnormal four-chamber views (62.9%). The detection rate was also higher if the scan was performed in the tertiary institution, and if there were other chromosomal or structural anomalies. Maternal BMI did not affect the detection rate in the current series. Stepwise logistic regression analysis showed that three independent variables affecting the detection rate were complexity of the cardiac lesion, experience of the operator, and the detection of chromosomal anomalies. CONCLUSION: A high detection rate for major CHDs can be achieved in a screening setting but there is still room for improvement in scanning skills in the four-chamber view and great-artery analysis in both tertiary and local centers.

Randomized comparison of the quality of realtime fetal ultrasound images transmitted by ISDN and by IP videoconferencing.

We compared the quality of realtime fetal ultrasound images transmitted using ISDN and IP networks. Four experienced obstetric ultrasound specialists viewed standard recordings in a randomized trial and rated the appearance of 30 fetal anatomical landmarks, each on a seven-point scale. A total of 12 evaluations were performed for various combinations of bandwidths (128, 384 or 768 kbit/s) and networks (ISDN or IP). The intraobserver coefficient of variation was 2.9%, 5.0%, 12.7% and 14.7% for the four observers. The mean overall ratings by each of the four observers were 4.6, 4.8, 5.0 and 5.3, respectively (a rating of 4 indicated satisfactory visualization and 7 indicated as good as the original recording). Analysis of variance showed that there were no significant interobserver variations nor significant differences in the mean scores for the different types of videoconferencing machines used. The most significant variable affecting the mean score was the bandwidth used. For ISDN, the mean score was 3.7 at 128 kbit/s, which was significantly worse than the mean score of 4.9 at 384 kbit/s, which was in turn significantly worse than the mean score of 5.9 at 768 kbit/s. The mean score for transmission using IP was about 0.5 points lower than that using ISDN across all the different bandwidths, but the differences were not significant. It appears that IP transmission in a private (non-shared) network is an acceptable alternative to ISDN for fetal tele-ultrasound and one deserving further study.

Minimum requirements for remote realtime fetal tele-ultrasound consultation.

We studied the transmission bandwidth required for accurate diagnoses when performing realtime fetal tele-ultrasound consultations. The study was divided into three phases. In phase I, three experienced clinicians evaluated the quality of ultrasound images transmitted at various bandwidths (internally looped back within Brisbane) using eight commercially available codecs at random. The two codecs that performed best proceeded to phase 2, in which a realtime video-link of up to 2 Mbit/s was set up between Brisbane and Townsville (1,500 km apart). Testing with a standard video-tape was performed at seven different bandwidths selected at random, with four clinicians (who were blinded to the equipment and bandwidths used). The optimum line rates for transmission were determined, and testing was then performed using these line rates for fetuses with various anomalies (phase 3). The results showed significant differences in performance according to bandwidths used, but not according to observers. Bandwidths were grouped into three levels. At level I (256 kbit/s) the performance was significantly worse than at level II (384, 512 or 768 kbit/s), which was in turn worse than that at level III (1, 1.5 or 2 Mbit/s). However, within each level, performance at one bandwidth was not significantly different from that at the others. The most cost-effective transmission rates therefore appeared to be 384 kbit/s and 1 Mbit/s. Further testing with fetuses affected by various anomalies confirmed that the majority could be diagnosed using a 384 kbit/s link, with slight improvement in evaluation when the bandwidth was increased to 1 Mbit/s.

Meconium thorax: a case report and review of literature.

A case is presented in which extension of meconium peritonitis through muscular defects in the diaphragm lead to intrathoracic calcifications diagnosed sonographically at 23 weeks of gestation. There were three diaphragmatic defects, two small ones corresponded to foramina of Morgagni and one large posterior defect that did not correspond to the foramen of Bochdelak. There were three additional muscular defects: one in the rectus abdominus and two, bilaterally, in the loins. Despite long-standing fetal ascites and fresh intraperitoneal meconium at laparotomy, postoperative progress was uneventful. The baby did not have other dysmorphic features except for a single palmar crease, the chromosomes were normal, and the baby did not have cystic fibrosis. Follow-up examination at 10 months showed a thriving infant with mild hypotonia and developmental delay, but no respiratory or gastrointestinal problems.