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Biomedical subjects

M H Tang

Publications and source records attributed to M H Tang.

At least 37 records · Page 2Linked to original sources
PubMed1999

Cardiac blood flow studies in fetuses with homozygous alpha-thalassemia-1 at 12-13 weeks of gestation.

OBJECTIVE: Fetuses affected by homozygous alpha-thalassemia-1 develop anemia as early as the first trimester. Our objective was to study hemodynamic indices in affected fetuses at 12-13 weeks of gestation to determine whether these would be useful in the prediction of anemia. DESIGN: Prospective observational study. SUBJECTS: Women referred before 14 weeks of gestation for the prenatal diagnosis of homozygous alpha-thalassemia-1. METHODS: Transabdominal and/or transvaginal Doppler sonography was performed to measure the flow velocities in the fetal ascending aorta and pulmonary artery at 12-13 weeks. The Doppler indices were compared between those that were subsequently confirmed to be affected by homozygous alpha-thalassemia-1 and those that were unaffected. RESULTS: Between June 1997 and April 1998, 60 eligible women were recruited. Doppler examination was successful in 58 fetuses. Of these, 22 were subsequently confirmed to be affected by homozygous alpha-thalassemia-1. The diagnosis was made by chorionic villus sampling and DNA analysis in two affected fetuses and by cordocentesis and hemoglobin evaluation in 20 affected fetuses. Hemoglobin concentrations could be measured in ten fetuses and these ranged from 4 to 8 g/dl. The affected fetuses had significantly higher peak velocities at the pulmonary valve and ascending aorta and a larger inner diameter of the pulmonary valve than that in unaffected fetuses. The total cardiac output was increased by one-third in affected fetuses and was mainly due to an increase of the right-side cardiac output. CONCLUSION: In the early stage of anemia, the fetus responds mainly by increasing its right-side cardiac output. However, there is extensive overlap of the values of cardiac output between the affected and the unaffected fetuses, precluding its use in the prediction of anemia.

Adult↗
PubMed1999

Prenatal sonographic features of spondylocostal dysostosis and diaphragmatic hernia in the first trimester.

Spondylocostal dysostosis is a congenital disorder characterized by multiple malformations of the vertebrae and ribs. We describe the sonographic features of an affected fetus at 12 and 14 weeks of gestation. The fetus had thoracic scoliosis, multiple vertebral and rib malformations and a grossly dilated stomach that had herniated into the chest through a left-sided diaphragmatic hernia. The stomach spanned the whole length of the fetal trunk.

Adult↗
PubMed1999

Nuchal translucency in fetuses affected by homozygous alpha-thalassemia-1 at 12-13 weeks of gestation.

OBJECTIVE: Fetuses affected by homozygous alpha-thalassemia-1 are anemic in the first trimester. We studied their nuchal translucency (NT) measurements at 12-13 weeks of gestation. METHODS: Nuchal translucency was measured prospectively in fetuses at risk of homozygous alpha-thalassemia-1. Measurements of those fetuses subsequently confirmed to be affected by homozygous alpha-thalassemia-1 but with a normal karyotype were compared to those of 440 controls. The controls were from the general obstetric population who had NT measurements at 12 or 13 weeks with known normal outcome. All the NT measurements were expressed as multiples of the median (MoM) for the gestational day. RESULTS: Between 1996 and 1998, 94 at-risk pregnancies were studied. Of these, 32 were subsequently confirmed to be affected by homozygous alpha-thalassemia-1. Chromosome study was not carried out in three cases and these were excluded from the analysis. Nuchal translucency MoMs for cases and controls were found to fit a log Gaussian distribution. The log means (standard deviation) for case and control NT MoM were 0.075 (0.156) and -0.0019 (0.091), respectively. The median NT MoM (95% CI) for cases was 1.19 (1.08-1.62) and was significantly higher than that of the controls (p < 0.001). However, there was extensive overlap of NT between cases and controls. CONCLUSION: Overall, there was a 19% increase in NT MoM in fetuses affected by homozygous alpha-thalassemia-1. This represents a difference of only 0.3-0.4 mm, which is clinically insignificant. This finding indirectly suggests that the increased NT in trisomic fetuses cannot be explained by fetal anemia. Conversely, the presence of increased NT in a fetus at risk of homozygous alpha-thalassemia-1 should alert one to the possibility of chromosomal abnormality rather than being attributed to fetal anemia.

Adolescent↗
PubMed1999

First-trimester ultrasound diagnosis of holoprosencephaly: three case reports.

We present three cases of fetal holoprosencephaly diagnosed by transabdominal and transvaginal ultrasound examinations at 10 and 13 weeks' gestation. The diagnosis was based on two sonographic criteria: first, the intracranial finding of a single ventricle with a cerebral mantle and no visible midline structures but fusion of the thalami and corpus striatum; and, second, facial abnormalities, including hypotelorism. The ultrasound findings were confirmed by embryoscopy before abortion in one case and by pathological examination after abortion in two cases. Chromosome study of the three fetuses showed trisomy 18, triploidy and mosaic 18p deletion and duplication.

Abortion, Therapeutic↗
PubMed1999

Sonographic features of fetal trisomy 18 at 13 and 14 weeks: four case reports.

Fetal trisomy 18 is the second most common multiple malformation syndrome. We present four cases of trisomy 18 with multiple sonographic abnormalities at 13 and 14 weeks of gestation. These cases demonstrated that fetal hand deformities can be a tell-tale sign of trisomy 18 with or without increased nuchal translucency at this gestation.

Abnormalities, Multiple↗
PubMed1999

Echogenic bowel in fetuses with homozygous alpha-thalassemia-1 in the first and second trimesters.

OBJECTIVE: Fetal echogenic bowel has been observed in fetuses with meconium peritonitis, cystic fibrosis, aneuploidy, congenital viral infection and intrauterine growth restriction. The pathogenesis of echogenic bowel is unknown, but it may be attributed to bowel ischemia. Fetuses affected by homozygous alpha-thalassemia-1 are severely anemic and hypoxic. We investigated the incidence of echogenic bowel in these hypoxic fetuses in the first and second trimesters. DESIGN: Prospective observational study. SUBJECTS: Women referred for the prenatal diagnosis of homozygous alpha-thalassemia-1 before 24 weeks' gestation. METHODS: All subjects had one or more abdominal and/or vaginal ultrasound examination between 12 and 24 weeks' gestation. Echogenic bowel was diagnosed if the bowel appeared either isoechogenic or more echogenic than the bone. RESULTS: Between March 1997 and July 1998, 126 pregnancies were studied. Thirty-six fetuses were confirmed to be affected by homozygous alpha-thalassemia-1, and 11 of them (31%, 95% CI 16-48%) had echogenic bowel. These observations were made before the invasive test results were available. None of the fetuses unaffected by homozygous alpha-thalassemia-1 had echogenic bowel. CONCLUSION: There is a strong association between homozygous alpha-thalassemia-1 and echogenic bowel. The pathogenesis is unknown. Speculations include bowel hypoperistalsis or bowel wall edema due to severe anemia and hypoxia.

Female↗
PubMed1999

Maternal serum alpha-fetoprotein and human chorionic gonadotrophin in pregnancies conceived after intracytoplasmic sperm injection and conventional in-vitro fertilization.

Data in the Caucasian population suggest that maternal serum alpha-fetoprotein (AFP) and unconjugated oestriol concentrations are reduced and human chorionic gonadotrophin (HCG) concentrations are elevated in pregnancies conceived after in-vitro fertilization (IVF), leading to a higher than expected Down's syndrome screen-positive rate. There are no previous reports on the serum marker values in pregnancies conceived after intracytoplasmic injection (ICSI). Between 1996 and 1998, we measured maternal serum total HCG and AFP concentrations between 15 and 20 weeks gestation in 42 in-vitro fertilization (IVF) pregnancies and 23 ICSI pregnancies with known normal outcome. The results were compared with that of 2799 naturally occurring singleton pregnancies who were known to have a normal outcome. Median AFP multiple of the median (MOM) in ICSI pregnancies was significantly reduced to 0.76 compared with both that of the controls and that of the IVF pregnancies. For the IVF pregnancies, median HCG MOM was elevated to 1.15, and median AFP MOM was reduced to 0.88 compared with the controls, but these differences were not statistically significant. In both the IVF and ICSI pregnancies the changes might result in a falsely high Down's syndrome risk. In particular, the reduced AFP concentration in ICSI pregnancies was substantial. If this preliminary finding is substantiated by other series, the appropriate adjustment needs to be made to allow for valid interpretation of the screen result and to avoid an unnecessarily high false positive rate.

Adult↗
PubMed1999

The association between maternal smoking and fetal hydranencephaly.

OBJECTIVE: To evaluate the relationship between maternal smoking and fetal congenital central nervous system malformations. METHODS: Retrospective review of all cases of fetal congenital malformations of the central nervous system (CNS) identified at or shortly after birth over a 10-year period (1986-1995) in a university teaching obstetric department. RESULTS: The total number of CNS abnormalities identified was 79, constituting 0.13% of all deliveries over the period (n = 59,392) and 4.7% of all congenital malformations (n = 1,678). The incidence of smoking mothers was 1.64% over the study period. Four babies had hydranencephaly, 3 of these mothers being smoking teenagers. The odds ratio of having a hydranencephalic fetus in smoking mothers compared to non-smokers was 56 (95% CI 7.41-427) in the group with CNS abnormalities, 136 (95% CI 14.5-1280) in the group including all congenital malformations, and 179 (95% CI 18.6-1719) in the group including all deliveries. CONCLUSION: Maternal smoking did not appear to increase the incidence of fetal congenital CNS abnormalities overall, but might be associated with particular vascular patterns of damage to the developing brain that could predispose to a hydranencephalic malformation.

Adolescent↗
PubMed1999

Prenatal diagnosis of congenital heart malformations: classification based on abnormalities detected by the four-chamber view.

The aim of the study was to provide logical steps, alternative to the sequential chamber analysis, for diagnosing major congenital heart malformation prenatally. Between 1988 and 1995, of the 14,885 high-risk pregnancies screened at the Departments of Obstetrics and Paediatric Cardiology, University of Hong Kong, 92 fetuses with major congenital heart malformations were detected at 17-36 weeks' gestation (mean=24.6 weeks) by extended fetal echocardiographic screening. These were classified according to obvious abnormalities related to the partition of the heart or ventricular dimensions depicted by the four-chamber view. Subgrouping according to the presence of normal or abnormal ventriculo-arterial connection, with or without outflow tract anomalies, was further attempted. Five groups were identified: (1) septal defects with all four chambers identified (n=62, 67 per cent); (2) intact septation with dilatation of either the right or all four chambers of the heart (n=12, 13 per cent); (3) intact septation with hypoplasia of either one of the ventricles (n=11, 12 per cent); (4) a rudimentary interventricular septum giving an apparent three-chamber heart (n=6, 7 per cent); (5) miscellaneous causes (n=1, 1 per cent). Combined with the information related to the ventricular outflow tracts, the accuracy of arriving at a definitive diagnosis was 97 per cent, when compared with postnatal investigations, surgery and/or autopsies. This simple classification could provide logical steps to arrive at a definitive diagnosis for most major fetal heart malformations.

Dilatation, Pathologic↗
PubMed1999

Sonographic diagnosis of limb reduction defects in a fetus with haemoglobin Bart's disease at 12 weeks of gestation.

Limb reduction defect is a rare event but is found in eight per cent of fetuses affected by haemoglobin Bart's disease. We present a case of haemoglobin Bart's disease with terminal transverse limb reduction defects of all four limbs diagnosed by abdominal ultrasound examination at 12 weeks of gestation. The pregnancy was terminated by suction curettage. Just prior to the procedure, transabdominal needle embryoscopy was performed and this confirmed the sonographic diagnosis. The present case demonstrates the need and feasibility of a detailed anatomic survey of a fetus affected by haemoglobin Bart's disease at 12 weeks. This is particularly relevant if the patient is considering the option of intra-uterine therapy.

Adult↗
PubMed1999

Risk of neural tube defects in the offspring of thalassaemia carriers in Hong Kong Chinese.

The risk of having an offspring with neural tube defect is negatively correlated with early pregnancy maternal folate levels. Thalassaemia carriers often have subnormal folate levels. We postulate that their offspring may be at increased risk of having neural tube defect. We retrospectively reviewed the records of 1961 Chinese women referred to a tertiary centre for prenatal diagnosis between January 1997 and August 1998. Women with a mean corpuscular volume greater than 80 fl were assumed not to be alpha-thalassaemia-1 or beta-thalassaemia heterozygotes. alpha- and beta-thalassaemia heterozygotes were diagnosed by haemoglobin studies. Of the 1961 women studied, pregnancy outcome was not available in 20 and thalassaemia screening was not available in 109 and these were excluded from the final analysis. Two-hundred-and-six women were alpha-thalassaemia-1 heterozygotes, 102 women were beta-thalassaemia heterozygotes and one woman had HbE disease. Three alpha-thalassaemia carriers and one beta-thalassaemia carrier had a pregnancy affected by anencephaly (odds=1:76). In the 1523 non-carriers, five pregnancies were affected by spina bifida (odds=1:304). The odds ratio (95 per cent confidence interval) for neural tube defects in the alpha- and beta-thalassaemia carriers was 3.99 (1.07 to 14.94; p<0.05, Chi-square test). Because of the small number of affected pregnancies studied, the finding needs to be substantiated by a larger series. If the increased risk is genuine, women need to be screened for thalassaemia before conception and the thalassaemia carriers should be given periconceptional folate supplement to reduce the occurrence of neural tube defects.

Asian People↗
PubMed1998

Ultrasound diagnosis of fetal diaphragmatic hernia and complex congenital heart disease at 12 weeks' gestation--a case report.

Congenital diaphragmatic hernia is commonly associated with congenital heart disease. Their coexistence indicates a poor prognosis. Prenatal diagnosis of these conditions in early pregnancy allows the option of pregnancy termination. We present a case of left-sided fetal diaphragmatic hernia and complex congenital heart disease diagnosed by ultrasound examination at 12 weeks' gestation.

Abortion, Induced↗
PubMed1998

Clinical significance of amniotic-fluid-cell culture failure.

Recent reports suggest an increased incidence of chromosomal abnormalities in pregnancies with amniotic fluid-cell culture failure. We retrospectively reviewed the cytogenetic results of 14,165 amniotic fluid samples processed in our laboratory from 1987 to 1996. Ninety-eight per cent of the samples were obtained before 24 weeks' gestation, mainly because of advanced maternal age; 2 per cent were obtained after or at 24 weeks because of the ultrasonographic finding of fetal structural defects. Amniotic-fluid-cell culture failure occurred in 62 cases (0.44 per cent). Culture failure was more common in samples obtained after or at 24 weeks' gestation (10 per cent) than in those obtained before 24 weeks (0.27 per cent) (P < 0.001, chi-square test). This difference was also observed when the results were analysed according to the cases with known normal or abnormal karyotypes. The frequency of culture failure did not differ significantly between the groups with normal and abnormal karyotypes. We conclude that amniotic-fluid-cell culture failure is more common in advanced pregnancy with an ultrasonographic finding of fetal structural defects and is not associated with a higher incidence of chromosomal abnormalities.

Amniotic Fluid↗
PubMed1998

Second-trimester maternal serum alpha-fetoprotein and human chorionic gonadotrophin screening for Down's syndrome in Hong Kong.

Second-trimester maternal serum screening for fetal Down's syndrome is well established in many Western countries. Its usefulness and acceptability is unknown in the Asian countries. Between June 1994 and December 1996, we offered second-trimester serum AFP and hCG screening to pregnant women in Hong Kong who were less than 35 years old and without other risk factors for chromosome abnormalities. Each woman was assigned a risk of having a Down's syndrome term pregnancy by using a computer software program that took into account her age. weight, AFP and hCG MOMs. All those with a risk of one in 250 or greater were designated screen-positive, subject to the revision of gestation by ultrasound examination. 9,177 women with singleton pregnancies (93 per cent were Chinese) were screened. The uptake of screening was 75 per cent. 281 women (three per cent) were initially classified to be screen-positive. After revision of the gestation by ultrasound examination, 183 women (two per cent) were 'true' screen-positive and 164 (90 per cent) accepted the offer of amniocentesis. Eight of these pregnancies were affected by Down's syndrome and all the women elected pregnancy termination. The odds of being affected, given a positive screening result, were one in 23. Six Down's syndrome pregnancies were missed by screening programme. The detection rate was 57 per cent. The study showed that second-trimester serum screening for fetal Down's syndrome was feasible and accepted in the Hong Kong population.

Adult↗