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Y H Lam

Publications and source records attributed to Y H Lam.

76 records · Page 5Linked to original sources
PubMed1995

Pregnancy screening by uterine artery Doppler velocimetry--which criterion performs best?

OBJECTIVE: To test whether repeating Doppler studies of the uteroplacental circulation late in gestation will improve the test's power for predicting pregnancy-induced hypertension and fetal growth restriction (FGR), and whether analysis based on a combination of quantitative and qualitative assessments of the uterine arterial waveforms will yield better results than analysis based on either alone. METHODS: A total of 358 patients considered to be at medium risk for the development of pregnancy-induced hypertension and FGR were recruited. Continuous-wave Doppler studies of the uterine arteries were performed serially at 20, 28, and 36 weeks' gestation. The values of various Doppler indices in the prediction of subsequent pregnancy complications were tested at different gestations and different cutoff levels. The overall significance of performance of the Doppler indices was assessed by the Cohen kappa index, which tests the extent of agreement between the test and the "truth" over that by random chance agreement. RESULTS: A total of 974 examination results on 334 patients were available for analysis. We found that Doppler studies of the uterine arteries at 28 and 36 weeks were less useful than studies performed at 20 weeks. Serial studies at 20 and 28 weeks showed only marginal improvement when compared with a single study at 20 weeks. The best criteria were a mean resistance index (RI) of uterine arteries above the 90th percentile and the presence of diastolic notches in both uterine arteries at 20 weeks. Although the overall kappa index only suggested fair to good agreement beyond chance, the positive predictive value for subsequent complications was good: 57% for severe complications and 93% for any complications. CONCLUSION: Doppler studies of the uterine artery as a test for the subsequent development of pregnancy complications are best performed at 20 weeks with a combination of RI measurements and the assessment of the presence of diastolic notches.

Adult↗
PubMed1994

Ultrasound measurement of placental thickness to detect pregnancies affected by homozygous alpha-thalassaemia-1.

Homozygous alpha-thalassaemia-1, a common cause of hydrops fetalis, is usually diagnosed invasively. We measured placental thickness by ultrasound at 10-21 weeks' gestation in 231 at-risk pregnancies. 60 were affected (by DNA analysis). The sensitivity and specificity in detecting affected pregnancies at cut-off of mean placental thickness plus 2 SD before 12 weeks' gestation were 0.72 (95% CI 0.52-0.93) and 0.97 (0.9-1.0). After 12 weeks sensitivity increased to 0.95 (0.89-1.0) and by 18 weeks reached 1.0 (0.60-0.99) without change in specificity. Selection of pregnancies at risk by measurement of placental thickness will reduce the number of invasive diagnostic procedures.

Female↗
PubMed1994

Umbilical artery Doppler velocimetry compared with fetal heart rate monitoring as a labor admission test.

A total of 155 patients admitted in early labor to the delivery unit of the University of Hong Kong were recruited into a study comparing the value of umbilical artery Doppler velocimetry and fetal heart rate (FHR) monitoring in early labor as an admission test. FHR monitoring for 30 min was recorded on admission, and umbilical A/B ratio was simultaneously performed. The FHR tracing was scored according to the Lyons score by a third independent observer after delivery. Outcome variables studied included small for gestational age (SGA), intrapartum FHR abnormalities, operative deliveries for fetal distress, umbilical cord pH, Apgar scores, admission into the special care baby unit, and a combination of the variables. It was found that at cut-off values of Lyons score < 7 and umbilical A/B ratio > 2.6 at term, about 19% of cases were abnormal for either tests, with only a few cases of overlap. Umbilical A/B ratio was found to be significantly correlated with SGA. The sensitivity and positive predictive values were, however, low. Both tests were relatively poor predictors for most of the outcome variables studied. Interestingly, FHR monitoring did not seem to have any advantage over Doppler velocimetry as a labor admission test. Further larger scale studies to evaluate their usefulness in medium and low risk populations are indicated.

Apgar Score↗