First-trimester maternal serum human chorionic gonadotrophin as a marker for fetal chromosomal disorders

The Dutch Working Party on Prenatal Diagnosis has initiated a study on the possibilities of first-trimester screening for fetal chromosomal disorders. We report on maternal serum human chorionic gonadotrophin (MS-hCG) measurements in 1348 pregnancies with a chromosomally normal fetus and 53 pregnancies with a chromosomally abnormal fetus. The median MS-hCG concentration in 24 pregnancies with Down's syndrome was 1.19 multiples of the normal median (MoM). The MS-hCG distributions in normal and Down's syndrome pregnancies did not differ significantly (t-test: t = 1.945, p >0.05). We also found no difference between normal pregnancies and pregnancies with other chromosomal disorders (six cases of trisomy 18, MoM = 0.80; four cases of sex chromosome abnormality, MoM = 1.01; 17 cases of chromosomal mosaicism in chorionic villi, MoM = 1.11). Selecting an upper limit at the 90th centile could detect 25 per cent of pregnancies with Down's syndrome. We conclude that, in the first trimester, MS-hCG as a screening factor for Down's syndrome is of minor value. However, MS-hCG could be a useful factor in a first-trimester screening programme based on a combination of markers.     

Birth prevalence of down's syndrome in England and Wales

The natural birth prevalence of Down's syndrome for England and Wales in 1974–1987 (i.e., the birth prevalence in the absence of prenatal diagnosis and the induced abortion of affected pregnancies) was estimated by applying the maternal age-specific birth prevalence derived from epidemiological studies to the number of births in single-year age groups tabulated by the Office of Population Censuses and Surveys (OPCS). On average, the natural birth prevalence was 12.6 per 10 000 births and increased slightly from 12.2 to 13.2 per 10 000 births over the 14-year period. Using data on induced abortions carried out on account of Down's syndrome reported to OPCS under the statutory abortion notification scheme, 14 per cent of affected births were avoided by the induced abortion of affected pregnancies, so that the actual birth prevalence of Down's syndrome was estimated at 10.8 per 10000 births. Using data on Down's syndrome births reported to OPCS under the voluntary congenital malformation notification scheme, the prevalence was 7.2 per 10000 births, so only 67 per cent of the estimated number of affected births were, in fact, notified to the scheme.     

Prenatal screening for chromosome abnormalities using maternal serum chorionic gonadotrophin,alpha-fetoprotein,and age

Human chorionic gonadotrophin (hCG) levels were assayed retrospectively in stored maternal serum samples from 78 chromosomally abnormal pregnancies and 410 controls matched for gestation and maternal age. The median serum hCG concentration in 49 pregnancies with Down's syndrome was significantly elevated, at 2.18 multiples of the normal median. Significantly reduced hCG concentrations were found in a group of four trisomy 18 pregnancies (all less than 0.4 multiples of the median). Eight cases of unbalanced chromosome rearrangements appeared to show some lowering of hCG levels, while there was no significant difference in the levels in the cases of trisomy 13, balanced translocations, and sex chromosome abnormalities. Maternal serum hCG alone is a better indicator of Down's syndrome pregnancies than maternal age or maternal serum alpha-fetoprotein (AFP), either individually or in combination, and provides a further virtually independent measure of risk. On the basis of our findings, screening for Down's syndrome using hCG and AFP results combined with maternal age risks is predicted to result in a higher detection rate (57 per cent) for a lower false-positive rate (5.0 per cent) than would be attainable by combined AFP and age screening (37 per cent detection at a 6.6 per cent false-positive rate).     

Amniotic fluid pregnancy-specific β1-glycoprotein (SP1) in fetal developmental disorders

Concentration of pregnancy-specific β1-glycoprotein (SP1) was studied in second and third trimester amniotic fluid from pregnancies with various fetal developmental disorders. The material consisted of 26 cases with chromosomal disorders and 19 cases with nonchromosomal fetal malformations. The SP1 concentration was elevated in two cases of Meckel's syndrome (mean + 2.7–4.0 S.D.) as well as in one case of fetal triploidy (mean + 22 S.D.), while it was normal in all other 14 different fetal disorders.     

Value of maternal serum unconjugated oestriol measurement in prenatal screening for Down's syndrome

We compared the medical and financial cost-effectiveness of prenatal serum screening for Down's syndrome using maternal age, serum alpha-fetoprotein and human chorionic gonadotrophin with and without the use of unconjugated oestriol. The use of unconjugated oestriol is medically more cost-effective than screening without it at all levels of detection. The actual performance depends on whether gestational age is estimated using ‘dates’ or an ultrasound scan. At a detection rate of 60 per cent, the proportion of unaffected fetal losses per case diagnosed at amniocentesis is about 22 per cent less if gestational age is estimated using dates (time since the first day of the last menstrual period) and about 47 per cent less if it is based on an ultrasound scan examination. At this detection rate, the inclusion of unconjugated oestriol increases costs by about £2k per case diagnosed (£36k instead of £34k) if gestational age is estimated using dates, but it is no more expensive if gestational age is measured from an ultrasound scan examination (indeed, it is more cost-effective at detection rates above 60 per cent). Since there is little change in the financial cost with the inclusion of unconjugated oestriol, for the improved medical performance of screening, it is worthwhile including it in the screening test.     

Maternal serum CA 125 levels in pregnancies with chromosomally-normal and -abnormal fetuses

We measured the maternal serum cancer antigen 125 (MS-CA 125) levels in 98 nonpregnant women, 765 first- and second-trimester pregnancies with chromosomally-normal fetuses, and 54 chromosomally-abnormal pregnancies. To determine the MS-CA 125 concentration, we used a new automated microparticle enzyme immunoassay with low inter-assay variability. The median MS-CA 125 level decreased from the first to the second trimester of pregnancy and was higher than that in non-pregnant women. We found no difference between normal and Down's syndrome (n = 29) pregnancies ( t-test: t = 0·57, p >0·5). The MS-CA 125 levels in pregnancies with other chromosomal abnormalities showed no difference either, compared with the normals. We conclude that MS-CA 125 is not a useful marker for fetal Down's syndrome, nor for other chromosomal disorders in pregnancy.     

Maternal serum free α- and free β-human chorionic gonadotrophin in pregnancies with insulin-dependent diabetes mellitus: Implications for screening for Down's syndrome

A study was performed to investigate the concentrations of the α and β free sub-units of human chorionic gonadotrophin (free α-hCG and free β-hCG) in maternal serum between 15 and 22 weeks of pregnancy in 126 pregnancies among 92 women with insulin-dependent diabetes mellitus (IDDM). Each IDDM pregnancy was matched with two control singleton pregnancies for gestational age (same completed week) and duration of sample storage (same calendar quarter). The median free α-hCG level in the IDDM pregnancies was 0·86 multiples of the median (MOM) for pregnancies without IDDM at the same gestational age (P<0·002) (95 per cent confidence interval 0·80–0·94). The corresponding free β-hCG level was 0·96 MOM (95 per cent confidence interval 0·85–1·09). These results enable free α-hCG values to be adjusted so that antenatal screening for Down's syndrome can be performed using this marker in IDDM pregnancies as well as in non-diabetic pregnancies.     

加强近岸海域环境监测保证海洋经济持续发展

近岸海域资源丰富，但近年来污染加重，灾害频繁，影响了海洋经济的发展和资源的可持续利用。本文论述了海洋环境监测与海洋资源可持续利用的关系，提出了如何加强近岸环境监测的对策。     

Directional change in a suite of foraging behaviors in tropical and temperate evolved honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

The concept of a suite of foraging behaviors was introduced as a set of traits showing associative directional change as a characterization of adaptive evolution. I report how naturally selected differential sucrose response thresholds directionally affected a suite of honey bee foraging behaviors. Africanized and European honey bees were tested for their proboscis extension response thresholds to ascending sucrose concentrations, reared in common European colonies and, captured returning from their earliest observed foraging flight. Race constrained sucrose response threshold such that Africanized bees had significantly lower sucrose response thresholds. A Cox proportional hazards regression model of honey bee race and sucrose response threshold indicated that Africanized bees were 29% (P<0.01) more at risk to forage over the 30-day experimental period. Sucrose response threshold organized age of first foraging such that each unit decrease in sucrose response threshold increased risk to forage by 14.3% (P<0.0001). Africanized bees were more likely to return as pollen and water foragers than European foragers. Africanized foragers returned with nectar that was significantly less concentrated than European foragers. A comparative analysis of artificial and naturally selected populations with differential sucrose response thresholds and the common suite of directional change in foraging behaviors is discussed. A suite of foraging behaviors changed with a change in sucrose response threshold that appeared as a product of functional ecological adaptation.Communicated by R.F.A. Moritz