Serum PAPP-A and free β-hCG are first-trimester screening markers for down syndrome

Serum measurements of pregnancy-associated plasma protein A (PAPP-A) and the free β-human chorionic gonadotrophin (hCG) subunit were made in 13 women with Down syndrome (DS) pregnancies and six other women with fetal aneuploidy ascertained at chorionic villus sampling (CVS), as well as 89 women with contemporaneous normal control pregnancies. Median serum PAPP-A measurements (0·31 MOM, 95 per cent confidence interval (CI) 0·22–0·65 vs. normal 1·06, 95 per cent CI 0·89–1·20) were lower and free β-hCG subunit measurements (1·13 MOM, 95 per cent CI 0·93–2·63 vs. normal 0·91, 95 per cent CI 0·79–1·03) were higher at statistically significant levels. Receiver operator characteristic (ROC) curves showed that the highest sensitivity for detection, 71·2 per cent (95 per cent CI 54·7–87·6 per cent), was for depressed PAPP-A levels; the combination of low serum PAPP-A levels, maternal age, and elevated free β-hCG levels yielded a detection rate of 78·9 per cent (95 per cent CI 64·9–92·8 per cent) of the affected pregnancies at 8–12 weeks' gestation.     

The association between alpha-fetoprotein and βhcg levels prior to and following chorionic villus sampling in cases that spontaneously miscarried

Maternal serum alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (βhCG) measurements taken prior to chorionic villus sampling (CVS) in 21 patients who subsequently miscarried were compared with measurements in a control group of 113 patients with uneventful pregnancies. Patients with AFP levels of 10 iu/ml or more prior to the CVS had a 4·3 times greater risk of miscarriage (95 per cent confidence interval 1·3–13·6). AFP levels obtained 1 week after the CVS in the 13 patients with late miscarriages were higher than in the control group (P = 0·06). Patients miscarrying had a greater rise in AFP (P = 0·06) and a greater fall in βhCG levels (P = 0·04) following the CVS procedure, compared with the control subjects. Each 10-unit change in the difference between AFP or βhCG levels prior to and 1 week following the CVS was associated with a significantly increased risk for late miscarriage. Elevated maternal serum AFP levels early in pregnancy and changes in AFP and βhCG levels following CVS may predict an increased risk for subsequent miscarriage.     

Maternal serum human chorionic gonadotrophin and pregnancy-associated plasma protein a,markers for fetal down syndrome at 8–14 weeks

Maternal serum levels of human chorionic gonadotrophin and its subunits (intact, α, and free βhCG) and pregnancy-associated plasma protein A (PAPP-A) were measured in 279 women between 8 and 14 weeks' gestation. This group included 23 pregnancies in which the fetus had Down syndrome (DS), diagnosed either at birth or during the second trimester (n=17) or from chorionic villus sampling (CVS) (n=6). Normal medians were determined from the 258 apparently normal pregnancies. The median levels of intact hCG (1·4 MOM) and free βhCG (2·1 MOM) were significantly raised, whereas the median level of PAPP-A (0·39 MOM) was significantly lower in the DS pregnancies when compared with the control group. Levels of αhCG were similar in both the control and the DS pregnancies. Analysis of samples taken prior to 14 weeks' gestation demonstrated that only PAPP-A (0·34 MOM) was significantly altered in DS pregnancies. However, after the exclusion of DS cases diagnosed at CVS, the median intact hCG (1·56 MOM), free βhCG (2·27 MOM), and αhCG (1·8 MOM) were all raised in DS pregnancies. This emphasizes the problem of the interpretation of biochemical markers when DS cases are diagnosed at CVS.     

Adjustment formulae for maternal serum alpha-fetoprotein,human chorionic gonadotropin,and unconjugated oestriol to maternal weight and smoking

Serum levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and un-conjugated oestriol (uE3) were measured in serum samples of 4131 non-smoking and 1018 smoking women during the second trimester of pregnancy. The levels of all three analytes decreased with increasing body weight. The AFP median was significantly increased in smokers in a dose-response association; hCG decreased by 21 per cent and uE3 decreased by 3 per cent in smokers in a non-dose-related fashion. Regression functions for adjustment of serum levels for weight and smoking should be considered in risk estimation for Down syndrome in order to give a woman's individual risk more precisely.     

Analysis of maternal serum alpha-fetoprotein and free beta human chorionic gonadotrophin in the first trimester: Implications for down's syndrome screening

The aim of this study was to determine the maternal population, pregnancy, serum alpha-fetoprotein (AFP) and free β subunit of human chorionic gonadotrophin (FβhCG) parameters in a large series of women attending prenatal clinics before 15 weeks' gestation and to assess the practical problems of population screening for Down's syndrome in the first trimester using these markers. Serum samples were collected from 8600 women attending prenatal clinic booking visits. Maternal serum AFP and FβhCG medians were calculated for each day of gestation (49–104 days), using both dates and ultrasound estimates of gestation. The effects of maternal weight, twin pregnancies, and threatened abortion on AFP and FβhCG levels were analysed. The median age of the population was 27.1 years and the median weight 62.1 kg. Twenty-six per cent of samples were collected before 70 days and 50 per cent before 78 days' gestation. Eighty-nine per cent of all samples had gestational estimates by dates, 60 per cent by ultrasound and 52 per cent by both dates and ultrasound. The AFP median was 5 kU/1 at 49 days, 5.9 kU/1 at 70 days, and 17.9 kU/1 at 100 days. The peak median FβhCG level was 66.4 ng/ml at 64 days, falling to 20.6 ng/ml at 100 days' gestation. Both AFP and FβhCG levels showed log Gaussian distributions but the standard deviation for AFP was 20 per cent greater than that found in the second trimester. AFP and FβhCG levels showed an inverse relationship with maternal weight and were increased in twin pregnancies (1.68 and 1.97 multiples of the median, respectively). AFP and FβhCG can be readily measured in a large screening population in the first trimester. Down's syndrome screening protocols based on these markers could be refined by the use of gestations in individual days but AFP is likely to be a less effective marker and detection rates are likely to be lower than in the second trimester. To realize the potential of first-trimester screening, more women should be encouraged to attend the prenatal clinic in early pregnancy and ultrasound dating should be carried out for all pregnancies at this stage.     

Chorionic villus sampling: Analysis of fetal losses to delivery,placental pathology,and cervical microbiology

A population of 1639 patients were seen for chorionic villus sampling (CVS). Embryonic death was identified at ultrasound in 5.3 per cent of patients. The number of patients undergoing CVS was 1551, with 1416 transcervical procedures and 135 transabdominal procedures. The most common indication for CVS was advanced maternal age. Spontaneous pregnancy losses identified by increased risk of pregnancy loss with increasing aspiration attempts. The total fetal loss for this population was 5.4 per cent with the pregnancy loss estimated due to procedure being 1.2 per cent. Analysis of placentae from patients having CVS and amniocen-tesis showed no differences. Microbiological assessment prior to CVS was similar to previous publications.     

Enhanced twin pregnancy detection within an open neural tube defect and down syndrome screening protocol using free-beta hCG and AFP

We have applied our multimarker approach of maternal serum alpha-fetoprotein (AFP) and free-beta human chorionic gonadotropin (hCG) for Down syndrome screening to multiple gestations to assess its efficacy for improved detection of twin and triplet pregnancies. This study matched 225 cases of twin pregnancy and 39 cases of triplet pregnancy each with ten singleton pregnancies based on gestational week, race, time to receive sample, time of year of sample, and geographical area. The ratios of the MOM for each group at the tenth, 50th, and 90th percentiles were compared by the Wilcoxon test. Risks for twins were calculated using Bayes' rule, the age-related incidence of twins, and the levels of AFP and free-beta hCG. The tenth, 50th, and 90th percentiles of free-beta hCG MOMs in twin and triplet cases were 0.85, 1.99, and 4.51, and 1.38, 2.78, and 4.07, respectively. For AFP, the MOMs at these percentiles were 1.26, 1.91, and 2.99, and 2.02, 2.68, and 5.30, respectively. The twin and triplet distributions for each marker were statistically significantly different from the singleton distributions (P<0.0001) and from each other (P=0.0012). At a twin risk cut-off of 1 in 50, 77.4 per cent of all twin gestations can be detected in a second-trimester AFP and free-beta hCG screening protocol with 5.1 per cent of singleton pregnancies falsely identified as at risk for twins. Our dual marker protocol for mid-trimester pregnancy screening combining AFP and free-beta hCG can identify over 77 per cent of twin pregnancies in women less than 35 years of age. This benefit may contribute to an improved outcome of pregnancy by early detection of multiple gestation.     

Risk-based prenatal screening for trisomy 18 using alpha-fetoprotein,unconjugated oestriol and human chorionic gonadotropin

Nine centres collaborated to examine the feasibility of a screening method for trisomy 18 that was based on assigning individual risk, using a combination of maternal age and measurements of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG). Second-trimester measurements of these analytes were obtained from 94 trisomy 18 pregnancies. In the 89 pregnancies without an associated open defect, the median levels for AFP, uE3, and hCG were 0.65, 0.43 and 0.36 multiples of the unaffected population median, respectively. The strongest individual predictor of risk for trisomy 18 was uE3, followed by hCG, AFP, and maternal age, in that order. Using a method of individual risk estimation that is based on the three markers and maternal age, 60 per cent of pregnancies associated with trisomy 18 would be detected at a risk cut-off level of 1:100, with a false-positive rate of about 0.2 per cent. One in nine pregnancies identified as being at increased risk for trisomy 18 would be expected to have an affected pregnancy. This risk-based screening method is more efficient than an existing method that is based on fixed analyte cut-off levels. Even though the birth prevalence of trisomy 18 is low, prenatal screening can be justified when performed in conjunction with Down syndrome screening and when a high proportion of women offered amniocentesis have an affected fetus.     

Abnormal maternal serum chorionic gonadotropin levels in pregnancies with fetal chromosome abnormalities

The alpha subunit of human chorionic gonadotropin (alpha-hCG), human chorionic gonadotropin (hCG) and alpha fetoprotein (AFP) were measured in the serum of 25 women with chromosomally abnormal fetuses between 18 and 25 weeks of gestation and in 74 normal pregnancies. AFP levels less than 0.5 multiples of the median (MoM) or greater than 2.5 MoM were observed in 24 per cent of the abnormal pregnancies and in 6.76 per cent of the normal pregnancies. A low concentration of hCG (< 0.25 MoM) was observed in 8 per cent of abnormals and in 2.7 per cent of normals while an elevated concentration of hCG (>2.5 MoM) was observed in 56 per cent of abnormals and in 1.35 per cent of normals. Elevated hCG-alpha (>2.5 MoM) was observed in 28 per cent of abnormals and in none of the normals. Determination of elevated levels of hCG-alpha or hCG resulted in detection of 68 per cent of pregnancies with chromosomally abnormal fetuses with a false positive rate of 1.35 per cent. Determination of both elevated and depressed gonadotropin levels resulted in detection of 76 per cent of abnormal pregnancies with a false positive rate of 4.05 per cent. Measurement of hCG and hCG-alpha in maternal serum samples can be used as a screening procedure for detecting pregnancies at risk for fetal chromosome abnormalities.     

Racial differences in maternal serum human chorionic gonadotropin and unconjugated oestriol levels

We assayed maternal serum samples from 134 black and 268 white women from 16 to 18 weeks of gestation for intact human chorionic gonadotropin (hCG), and unconjugated oestriol (uE3). Serum from women with high ( ⩾ 2·5 MOMs) or low (risk for Down syndrome ⩾ 1/365) maternal serum alpha-fetoprotein (MSAFP) levels were excluded. After correcting for maternal weight, we found that median hCG levels were 16 per cent higher in black women but uE3 levels were not significantly different. These results confirm three other studies for hCG and one study for uE3. Corrections are recommended for both maternal serum hCG and AFP before calculating the risk for Down syndrome in black women.     

First-trimester aneuploidy screening using serum human chorionic gonadotropin (hCG), free ahCG,and progesterone

Immunochemical serum assays for human chorionic gonadotropin (hCG), the free ohCG subunit, and progesterone (P) were considered separately and in combination for their ability to screen for chromosomally abnormal pregnancies in the first trimester. Maternal serum was collected from 141 women undergoing chorionic villus sampling at 9–12 menstrual weeks. Trisomy 21 pregnancies had significantly higher hCG levels, while trisomy 18 and 13 pregnancies had markedly lower hCG and progesterone levels than those of chromosomally normal pregnancies. However, the discrimination of normal from aneuploid pregnancies was poor with either hCG alone, progesterone alone, or free ahCG alone. Much improved discrimination was obtained by combining hCG, free ahCG, and P into an aneuploidy index [(P/hCG)(free ahCG/hCG)]. This index distinguished 9 out of 17 (53 per cent) of the trisomy 21 pregnancies, while only misidentifying 5 out of 112 (4.5 per cent) of the normal pregnancies. The aneuploidy index thus appears promising as a first-trimester biochemical screen for aneuploid pregnancies.     

Attitudes to prenatal screening,diagnosis and research among pregnant women who accept or decline an alpha-fetoprotein test

The aim of the study was to describe the opinion of pregnant women who had accepted or declined an alpha-fetoprotein (AFP) test, not only on AFP screening in general, but also on whether every pregnant woman should be offered amniocentesis (AC)/chorionic villus sampling (CVS) and an ultrasound scan for fetal malformations. An additional aim was to describe pregnant women's attitudes concerning continued research in the prenatal field. The study was performed as a questionnaire study in two regions over a 1-year period from 1 October 1988 to 30 September 1989. Results are based on answers from 3331 women who had taken an AFP test and 336 women who had declined the offer of a test. A total of 79 per cent of the women thought that an AFP test, 70 per cent that an ultrasound scan for fetal malformations, and 26 per cent that AC or CVS should be offered to all pregnant women. Fifty-nine per cent of the women were positive towards continued research in the prenatal field. Women who had had an AFP test were generally much more positive towards screening and research than women who had declined, who were generally against. Women who had left school without a high school degree were on average more positive towards the screening issues than women who had this degree. In conclusion, the results obtained in this study strongly suggest that women's attitudes are very dependent on how the prenatal screening programme is already organized in their local area.     

Prospective intervention trial of a screening protocol to identify fetal trisomy 18 using maternal serum alpha-fetoprotein,unconjugated oestriol,and human chorionic gonadotropin

Two prenatal centres in New England, routinely using a screening protocol for fetal Down syndrome that included maternal serum alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG) measurements in combination with maternal age, adopted a separate screening protocol for trisomy 18. That protocol identified a pregnancy as being at high risk when AFP, uE3, and hCG measurements all fell at or below specified cut-offs (0.75, 0.60, and 0.55 multiples of the median, respectively), regardless of maternal age. Among the first 19 491 women screened, 98 (0.5 per cent) were found to have values which placed them in the high-risk category. Four of these women were subsequently found not to be pregnant. In two others, samples from non-pregnant individuals were found to have been incorrectly submitted for analysis in place of the samples from the pregnant women. All of the remaining 92 women were counselled and offered amniocentesis and fetal karyotyping. Eighty-eight (96 per cent) accepted. Karyotypes or birth outcomes were available on all 92 pregnancies. Six cases of trisomy 18 and one case of Turner syndrome were identified by karyotype. One case of trisomy 18 was identified for every 14 unaffected pregnancies offered amniocentesis. In the present prospective study, an estimated 85 per cent of the cases of trisomy 18 were identified. However, given the small number ofcases (six), the 95 per cent confidence interval for the detection rate is broad (40–95 per cent).     

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).     

Down's syndrome screening in multiple pregnancies using alpha-fetoprotein and free beta hCG

Second-trimester distributions of the free beta human chorionic gonadotrophin (hCG) and alpha-fetoprotein (AFP) levels in 420 twin and 19 triplet pregnancies were measured and compared with the distributions in 6661 singleton pregnancies. On average, the levels of both analytes were twice as high in twins and over three times as high in triplets. Eight sets of twins discordant for Down's syndrome showed elevated levels of free beta hCG and reduced levels of AFP after correction of the multiple of the median for the presence of a twin pregnancy. Screening for Down's syndrome using the twin correction of the multiple of the median is expected to achieve a 51 per cent detection rate at a 5 per cent false-positive rate using these two markers.     

Maternal serum markers in second-trimester oligohydramnios

The levels of the maternal serum markers alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG), and unconjugated oestriol (uE₃) in 35 pregnant women with early second-trimester oligohydramnios differed from those in a reference population of 1699 singleton pregnancies. Maternal serum AFP levels above the 95th centile of the population distribution were observed in 80 per cent (16/20) of oligohydramnios cases with a normal fetus and in only 20 per cent (3/15) of the cases with a fetus displaying urogenital tract malformations. Elevated levels of hCG (above the 95th centile) and decreased levels of uE₃ (below the fifth centile) were encountered in 26 per cent (9/35) and 17 per cent (6/35) of the women, irrespective of the fetal condition. The abnormal profile of the serum markers in early second-trimester oligohydramnios resulted in 57 per cent (20 out of 35) of screen-positive cases for either fetal Down's syndrome or neural tube defects, compared with 8·4 per cent (143 out of 1699) in the reference population.     

Evaluation of transcervical chorionic villus sampling with a completed follow-up of 1550 consecutive pregnancies

Data from 1550 consecutive pregnancies after first-trimester prenatal diagnosis by transcervical chorionic villus sampling (TC-CVS) are presented. The sampling efficacy was 97.8 per cent; the mean amount of collected villus tissue was 23 mg (range 5–100 mg). There were 97 affected fetuses, mainly (73.2 per cent) with a chromosomal abnormality or a male karyotype in carriers of X-linked disease. Pregnancy termination in these and four other women for social reasons resulted in 1449 continuing pregnancies. In these pregnancies, the fetal loss rate up to 28 weeks of gestation was 5.1 per cent with the highest loss rate (3.9 per cent) before 16 weeks. When relating this fetal loss rate to maternal age, this was 6.1 per cent in the advanced maternal age group (⩾36 years) against 3.1 per cent in the younger age group. In 1376 pregnancies continuing beyond 28 weeks, the perinatal mortality rate was 1.1 per cent; the percentage of non-genetic congenital anomalies was 0.9 per cent. The reproductive pattern of women at high genetic risk after CVS followed by pregnancy termination was evaluated. Within 12 months after the first CVS followed by pregnancy termination, 70 percent of women again requested CVS in a subsequent pregnancy.     

Fetal ductus venosus flow velocity waveforms and maternal serum afp before and after first-trimester transabdominal chorionic villus sampling

Doppler flow velocity waveform recording in the fetal ductus venosus and umbilical artery as well as maternal blood sampling for serum alpha-fetoprotein (MSAFP) was performed before and after transabdominal chorion villus sampling (TACVS) in 36 women of advanced maternal age (≥ 36 years). Gestational age ranged between 11 and 13 weeks. No chromosomal anomaly was detected. No statistically significant difference was observed in ductus venosus velocity parameters or in the umbilical artery pulsatility index (PI) before and after CVS in 35 women with a normal pregnancy outcome. One case resulted in fetal loss. Post-CVS median MSAFP levels at 12 weeks (25 kIU/1) and 13 weeks (35 kIU/1) were significantly higher than pre-CVS levels. In three cases, post-CVS MSAFP levels were higher than 600 kIU/1, correlating with feto-maternal transfusions of approximately 1.0–1.4 ml, i.e., of around 40 per cent of feto-placental blood volume. One of these cases displayed absence of fetal peripheral blood flow velocities and fetal bradycardia following TACVS, resulting in fetal loss 1 week later. The remaining two cases had a normal pregnancy outcome, but showed a more than 50 per cent reduction in ductus venosus velocity after TACVS, whereas umbilical artery PI remained unchanged. However, similar velocity changes were associated with only small feto-maternal transfusions. Umbilical artery PI values remained unchanged.     

First-trimester maternal serum schwangerschafts protein 1 (SP1) in pregnancies associated with chromosomal anomalies

The relationship between first-trimester maternal serum Schwangerschafts protein 1 (SP1) and the karyotype of the pregnancy was examined in 692 women who underwent chorionic villus biopsy at 6–12 weeks. There were 30 pregnancies with abnormal karyotypes, consisting of 14 Down's syndrome (DS), eight trisomy 18, and eight other anomalies, two of which were mosaics. The normal ranges and medians for gestation were defined from the 662 cases in which the karyotype was normal. The median SP1 (0·5 MOM) of the abnormal group was significantly lower than that of the normal group (10 MOM). This relationship was maintained for the DS pregnancies (0·4 MOM) and for anomalies other than trisomy 18 (0·43 MOM) but not trisomy 18 (1·1 MOM). It is possible that the use of SP1 as a screening test for chromosome anomalies in the first trimester could have a 43 per cent detection rate for a 5 per cent false-positive rate.     

An association between fetal abdominal wall defects and elevated levels of human chorionic gonadotropin in mid-trimester

We analysed maternal serum human chorionic gonadotropin (hCG) in 16 pregnancies with fetal abdominal wall defects previously identified prenatally by elevated maternal serum alpha-fetoprotein (AFP) or at birth. The AFP levels had a mean of 6·38 MOM (range 0·34–15·65), as expected with these defects. The hCG levels had a mean of 1·82 MOM (range 0·23–4·11). The hCG levels in five pregnancies (31·25 per cent) were above 2·30 MOM. Elevated levels of hCG may be associated with fetal abdominal wall defects.