Notizen: Objectives 1. To compare the ultrasound biparietal diameter and crown-rump length of fetuses with and without Down's syndrome in the first half of pregnancy; 2. To investigate the effect of estimation of gestational age using either measure on the detection rate of serum screening for Down's syndrome.Design Matched case-control study. Cases were singleton Down's syndrome pregnancies with a biparietal diameter or a crown-rump length recorded. Five controls were matched to each case on: medical centre; the date of the ultrasound scan examination (within two years); gestational age measured as the number of days since the first day of the last menstrual period; and the ultrasound measure used (ie the biparietal diameter (the measure of choice), or the crown-rump length otherwise). If a woman had a serum screening test for Down's syndrome, the biparietal diameter or crown-rump length measurement had to be taken prior to the screening test so that the result of the test could not influence whether a scan was performed.Setting Ten antenatal screening centres in seven countries in Europe and North America.Subjects Two hundred and one women with singleton Down's syndrome pregnancies and 1005 women with unaffected singleton pregnancies.Results The median biparietal diameter of fetuses with Down's syndrome was identical to that among the controls (median difference 0.0mm, 95% confidence intervals (CI)–0.5 to 0.5mm). The estimates of gestational age based on biparietal diameter yielded a median gestational age less than that based on the women's last menstrual period: three days less for cases and two days less for controls; small but statistically significant differences probably reflected a minor systematic difference in the conversion of a biparietal diameter to a gestational age estimate. The median crown-rump length of fetuses with Down's syndrome was also identical to that among controls (median difference 0.0mm, 95% CI–1.5 to 2.0 mm). There was no significant difference between the median gestational age estimate based on crown-rump length and that based on the women's last menstrual period.Conclusion In antenatal screening for Down's syndrome the routine use of an ultrasound biparietal diameter or crown-rump length measurement to estimate gestational age will not adversely affect the detection rate. To avoid differences in gestational age estimates using the last menstrual period and the biparietal diameter influencing screening performance, separate medians should be derived for each serum marker using the two methods of estimating gestational age. The appropriate set of medians can then be used to calculate the multiple of the median value for each woman screened depending on the method used to estimate her gestational age.

Notizen: Objective To estimate the fetal loss of Down's syndrome fetuses between the time of chorionic villus sampling (10 weeks gestation) and the time of amniocentesis (16 weeks gestation) and term in women aged 35 years and older.Design The age specific prevalence rates in the first trimester of Down's syndrome were estimated using the Danish cytogenetic register in combination with results from four published studies. These were compared with the reported prevalence at the time of amniocentesis and at birth.Subjects 5927 singleton pregnancies undergoing chorionic villus sampling (71 cases of Down's syndrome and 5856 unaffected cases). This was combined with published data on a further 231 cases of Down's syndrome and 16620 unaffected cases.Main outcome measures Age specific prevalences at the time of chorionic villus sampling. Proportion of pregnancies lost between the time of chorionic villus sampling and the time of amniocentesis and term.Results Thirty-two percent of Down's syndrome pregnancies are lost between the time of chorionic villus sampling (10 weeks) and the time of amniocentesis (16 weeks) and 54% are lost by term.Conclusions The high fetal loss rates of Down's syndrome between the time of chorionic villus sampling and term introduce problems when evaluating first trimester screening tests with respect to their effective detection rates at term. A recommendation for quoting term risks is made.

Notizen: Objective To determine how frequently hydatidiform mole will be detected in a maternal serum Down's syndrome screening programme.Design Affected pregnancies were identified using a national register. Unconjugated oestriol (μE3) and human chorionic gonadotrophin (hCG) were measured in stored serum samples and alphafetoprotein (AFP) levels were available from previous neural tube defect screening at 15–20 weeks gestation.Subjects Ten pregnancies with a complete mole (i.e., hydropic placenta without a fetus), nine with stored serum samples and one with an AFP level only.Results The median values were 0.08, 0.13 and 1–83 multiples of the normal median for AFP, uE3 and hCG respectively. Six out of nine (67%) tested for all three markers had a high risk of Down's syndrome given maternal age and the marker levels.Conclusion Many molar pregnancies that have not presented clinically before 15 weeks will be detected through Down's syndrome screening.

Notizen: Objective— To investigatc the rcason for low matcrnal scrum unconjugated oestriol (uE3) and raised human chorionic gonadotrophin (hCG) levels in Down's syndrome pregnancies.Design— Mcasurement of uE3, total oestriol (tE3), dehydroepiandrosterone sulphate (DHEAS), a precursor of oestriol, and hCG in 15–20 week amniotic fluid samples from pregnancies with and without Down's syndrome.Setting— The retrieval and use of stored amniotic fluid samples collected from women who had had an amniocentesis for antenatal diagnosis.Subjects— 45 women with a Down's syndrome pregnancy and 224 unaffected controls of the same gestational age.Results— The median level of amniotic fluid in affected pregnancies was low for uE3, tE3 and DHEAS but high for hCG: 0.50,0.46,0.35 and 1–58 multiples of the normal median, respectively.Conclusion— These results suggest that the abnormal maternal serum levels of uE3 and hCG in affected pregnancies are due mainly to abnormal feto-placental synthesis, rather than feto-maternal transfer.

Notizen: The fetal femur length determined by an ultrasound examination at between 13 and 39 weeks gestation in 83 pregnancies associated with Down's syndrome was statistically significantly less than the expected value for pregnancies with the same biparietal diameter examined in the same ultrasound department (P〈0.0001). Expected values were based on linear regressions of femur length on biparietal diameter in 1340 control pregnancies from 27 ultrasound departments. The median value for the affected pregnancies was 0.94 times the expected value (95% CI 0.92 to 0.97). Eleven per cent of affected and 14% of control pregnancies had values ≤0.85 times the expected. The reduction in femur length in affected pregnancies was not related to biparietal diameter or to maternal age. Fetal femur length may be useful as an ancillary screening variable in the antenatal screening for Down's syndrome.

Notizen: Summary. All 103 amniotic fluids with positive gel-acetylcholinesterase (AChE) test results, obtained in Oxford between July 1980 and March 1983, were tested for the presence of fetal calf serum using a counter-immunoelectrophoresis test for bovine serum albumin. None of the samples from pregnancies associated with neural-tube defect (85), exomphalos (nine) and intrauterine death (four) had a positive fetal calf serum test, suggesting little or no immunological cross-reaction between the antiserum used in the test and amniotic fluid proteins. Among the remaining five samples, from unaffected pregnancies (two bloodstained and three clear), two had positive fetal calf serum test results (both were clear samples). The fetal calf serum test is therefore a useful technique capable of identifying false-positive AChE test results, without mis-classifying true-positive results as false-positive.