First-trimester alpha-fetoprotein screening for Down syndrome

Screening for Down syndrome and other chromosomal aneuploidies by biochemical parameters in maternal serum is well established for the second trimester. With screening as late as 16 weeks of gestation, the option of chorionic villus sampling (CVS) unfortunately is lost. In our study population, the maternal serum alpha-fetoprotein (MSAFP) concentration was determined in 2471 women in the first trimester immediately prior to CVS. Although in this sample MSAFP tended to be lower in Down syndrome (DS) pregnancies than in pregnancies with a chromosomally normal fetus, at this early gestational age neither a fixed cut-off level of 0·5 multiples of the normal median (MOM) nor one of 0·6 MOM was suitable for identifying pregnancies at higher risk for DS. This also applied to trisomy 18, although on average MSAFP in trisomy 18 pregnancies was lower than in normal and DS pregnancies.     

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.     

Implications of maternal serum alpha-fetoprotein elevation caused by transabdominal and transcervical CVS

Of 2882 women allocated to either transabdominal CVS (TA) or transcervical CVS (TC) at two large obstetric centres in Denmark, 2707 had blood samples drawn before and 30 min after CVS for maternal serum-alpha-fetoprotein (MSAFP) measurement. 2535 of these women had cytogenetically normal pregnancies and 2091 of them went on to have samples drawn at the 18–20 week follow-up. Post-procedure MSAFP values were correlated to the biopsy method used, with mean MSAFP values significantly higher after TA than TC, 33 and 15 kU/l, respectively (P<0·001). Following TA procedures, 18 per cent of cases had feto-maternal transfusion higher than 0·1 ml; this occurred in only 5 per cent of TC cases. MSAFP levels were associated with spontaneous fetal loss in the TA group but not in the TC group. TC, however, was followed by more losses than TA. The post-CVS MSAFP value was positively correlated with the amount of villi aspirated. The difference in post-procedure elevation in MSAFP 30 min later (average 18 kU/l higher for TA than for TC) was not reflected in raised levels at the 18–20 week follow-up. Study medians at mid-trimester did not differ from reference group medians established from a group of singleton pregnancies with sonographically determined gestational age who did not experience invasive procedures and delivered normal infants. Our findings suggest that CVS does not compromise mid-trimester MSAFP for screening for neural tube defects (NTDs). Extremely high mid-trimester MSAFP values in the TC group could predict imminent loss.     

Increased maternal serum alpha-fetoprotein and human chorionic gonadotropin in compromised pregnancies other than for neural tube defects or Down syndrome

Intrauterine fetal death occurred in four women who were ‘screen-positive’ in a screening programme for neural tube defects (NTDs) and Down syndrome (DS). These women had very high levels of maternal serum alpha-fetoprotein (MSAFP) and maternal serum human chorionic gonadotropin (MShCG). Therefore, we evaluated all ‘screen-positive’ women in whom both of these markers were ⩾ 2.0 multiples of the median. The cases fulfilling these criteria totalled 11, and only one of them had no complications. High concentrations of both MSAFP and MShCG in a number of these cases might have been caused by an increased placental volume, which, in turn, might have been induced by decreased perfusion of the placenta. We conclude that screening programmes wrongly determine a high risk of fetal NTD or DS if the concentrations of both these parameters are very high. Invasive diagnostic procedures should be avoided in these cases, particularly in view of the increased risk of an adverse pregnancy outcome.     

Maternal serum free beta hCG screening: Results of studies including 480 cases of down syndrome

The median maternal serum free beta human chorionic gonadotropin (hCG) multiple of the median (MOM) of 480 Down syndrome cases in the second trimester was 2·64, significantly greater than the reported median MOM of intact hCG (p<0·0001). In 234 of these cases from retrospective and prospective studies, the effectiveness of maternal serum free beta hCG was evaluated in combination with alpha-fetoprotein (AFP) and maternal age in second-trimester Down syndrome screening. Down syndrome detection in the gestational age range of 14–16 weeks was 82 per cent. In all gestational weeks (14–22), a 77·7 per cent Down syndrome detection rate was achieved. In prospective screening of 44 272 patients under the age of 35 years, 69 per cent of Down syndrome cases were detected (73 per cent in gestational weeks 14–16). The false-positive rate for the prospective study was 3·8 per cent. The use of free beta hCG combined with maternal serum AFP and maternal age-related risk for Down syndrome in a screening population (i.e., women under 35 years) yields an improved detection efficiency over other protocols.     

Maternal urinary β-core fragment of hCG/creatinine ratios and fetal chromosomal abnormalities in the second trimester of pregnancy

Our aim was to evaluate the potential value of the ratio of the maternal urinary beta-core fragment of human chorionic gonadotropin (βC-hCG) to creatinine (Cr) in discriminating between normal pregnancies and pregnancies associated with fetal chromosomal abnormalities. We hypothesized that pregnancies with fetal chromosomal abnormalities had abnormal quantities of βC-hCG in the urine. The aims of the present study were to investigate retrospectively whether maternal urinary ratios of βC-hCG/Cr are abnormal in women carrying fetuses with chromosome aberrations and to determine normative median values and a reference range for βC-hCG/Cr between 14 and 19 weeks' gestation. Maternal urinary βC-hCG and Cr concentrations were measured in 150 healthy women from 14 to 19 weeks and compared with ten cases of fetal chromosomal abnormalities matched for gestational age. The preliminary cut-off points corresponded to 0·29 multiple of the normal median (MOM) and 2·83 MOM, which were equivalent to the tenth and 90th centiles of the normal range. Of ten cases of fetal chromosomal abnormalities, one out of one (100 per cent) case with trisomy 18 and three of four (75 per cent) cases of variant 9 chromosome had low βC-hCG/Cr (≤0·29 MOM). One of five (20 per cent) cases with Down syndrome had elevated βC-hCG/Cr (≤2·83 MOM). Urinary βC-hCG/Cr ratios obtained in the second trimester may be useful for improved detection efficiency of Down syndrome, trisomy 18, and inversion of chromosome 9. Second-trimester maternal urinary βC-hCG/Cr should be investigated further as a potential marker for fetal chromosome anomalies.     

Early amniocentesis and fetal nuchal translucency in women requesting karyotyping for advanced maternal age

Fetal nuchal translucency was measured at 11–14 weeks' gestation in 97 pregnancies referred for early amniocentesis for advanced maternal age. The nuchal translucency was abnormal in 11 fetuses and the fetal karyotype was abnormal in five of these 11 cases. The karyotype was normal in 86 cases with normal nuchal translucency. The culture failure and miscarriage rates associated with early amniocentesis were 3·3 per cent and 2·2 per cent respectively. Amniotic fluid leakage occurred in 6 per cent of cases. In women requesting fetal karyotyping for advanced maternal age without additional biochemical screening, fetal nuchal translucency should be measured at 11–14 weeks. If the nuchal thickness is ≥ 3 mm, a first-trimester diagnostic procedure is indicated; however, if it is <3 mm, amniocentesis should be delayed until 16 weeks' gestation.     

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 alpha-fetoprotein and human chorionic gonadotropin screening for chromosome defects

The aim of this study was to determine the efficacy of combined maternal serum alpha-fetoprotein (MSAFP) and maternal serum human chorionic gonadotropin (MShCG) screening in detecting chromosome defects in the first trimester of pregnancy. Sera of 492 women (previously assayed for MSAFP) were analysed for MShCG under code without knowledge of cytogenetic results. Overall, 48 of 492 patients (9·8 per cent) had either an MSAFP multiple of the median ⩽0·5 or an MShCG β/a z ratio multiple of the median ⩽ 0·25, eight of whom had a fetus with a serious chromosome defect. A third of fetuses with Down' s syndrome and 83 per cent with trisomy 18 were detected at a potential‘cost’ of providing chorionic villus sampling or amniocentesis in 8·6 percent of women screened.     

Transabdominal villus sampling in early second trimester: A safe sampling method for women of advanced age

Transabdominal chorionic villus sampling (TA-CVS) was performed in 707 viable singleton pregnancies to exclude chromosomal abnormalities. Maternal age ranged between 36 and 49 years (mean 37·9 years); gestational age varied between 10·2 and 18·3 weeks (mean 13·3 weeks). In 639 women (90·4 per cent), a sufficient amount of chorionic tissue (⩾ 10 mg) was obtained after one needle insertion; in 66 women (9·3 per cent) two insertions were needed. An abnormal chromosome pattern was established in 19 cases (2·9 per cent). Vaginal bleeding or spotting within 28 days after TA-CVS occurred in 11 cases (1·5 per cent). The completed follow-up of 678 chromosomally normal pregnancies showed an overall fetal loss rate of 2·6 per cent before 28 weeks. The overall perinatal mortality was 0·9 per cent. When relating fetal loss to gestational age at TA-CVS, this was 6·6 per cent in women sampled before 12 weeks against only 1·8 per cent after 12 weeks. At the same time, the percentage of fetal loss occurring within 2 weeks following the procedure was 75 and 30 per cent, respectively. It is suggested that these data reflect the decline in spontaneous abortion rate during this particular period of pregnancy. It is concluded that TA-CVS is an effective procedure which, when performed after the natural decrease of fetal loss, appears to be a safe option for women of advanced maternal age.     

Maternal serum alpha-fetoprotein levels and fetal outcome in early second-trimester oligohydramnios

Early second-trimester oligohydramnios was associated with normal maternal serum alpha-fetoprotein (MSAFP) levels in nine out of 26 cases (35 per cent). Congenital malformations of the fetal urinary tract resulting in fetal anuria were present in nine cases; in seven of them, normal MSAFP levels were measured. In contrast, normal MSAFP levels were established in only 2 out of the 17 cases without fetal malformations. These data suggest that fetal urine is the major source of elevated AFP in the maternal compartment in early second-trimester oligohydramnios. This is further supported by the lack of any relationship between concentrations of MSAFP non-reactive with Concanavalin A, originating mainly from the yolk sacderived amniotic fluid AFP pool, and the presence of fetal diuresis. Three out of 26 women had experienced early second-trimester oligohydramnios in a previous pregnancy, suggesting the existence of a recurrence risk for this condition.     

Screening maternal serum alpha-fetoprotein levels and human parvovirus antibodies

The association between gestational infection with human parvovirus (B19) and fetal loss has increased interest in this virus and demand for diagnostic testing. However, serological assays for B19 are not yet widely available. Maternal serum alpha-fetoprotein (MSAFP) testing is commonly used during the second trimester to screen for various fetal defects. We attempted to determine whether an elevated level of MSAFP would be an appropriate indication for B19-specific tests. Over a 26-month period, MSAFP tests were performed at Michigan State University for 21 392 women. Sera remaining after that testing were stored frozen. Of these, 22 case samples—from women with MSAFP levels greater than 3·0 multiples of the median (MOM) and pregnancies that ended in fetal loss—and 44 matched control samples—from women with MSAFP levels greater than 0·4 and less than 2·2 MOM and live births at term—were tested for B19 antibodies. None of the 66 samples was IgM positive, while 33 (50 per cent) were IgG positive. The presence of IgG was not significantly associated with case or control status (matched odds ratio=0·77, 95 per cent confidence interval 0·28–2·11). These findings are consistent with other studies indicating prior infection in approximately half of adults and suggest that elevated screening MSAFP levels, in the absence of other evidence of B19 infection, should not prompt B19-specific testing.     

Screening for Down's syndrome in older women based on maternal serum alpha-fetoprotein levels and age: Preliminary results

We report the results of screening for Down's syndrome (DS) in older women using published rate schedules based on maternal serum alpha-fetoprotein (MSAFP) and age. Five hundred and seventeen patients aged 35 years and older, who were referred for a mid-trimester genetic amniocentesis, were first tested for MSAFP and then underwent an amniocentesis. Individual risks for DS, combining MSAFP and age, were derived using three different published rate schedules. Theoretical selection for amniocentesis was made using the cut-off level of the average collective risk for a 35-year-old woman (1:380 at live birth or 1:270 at amniocentesis). Six affected pregnancies (five with DS and one with trisomy 18), which were diagnosed prenatally, were all found to be at a higher risk than the specified cut-off. These cases would have been diagnosed in any event, using any of the published rate schedules. According to these rate schedules, between 39 and 45 per cent of the patients would be in the lower risk group and therefore would have been counselled not to undergo amniocentesis. Further studies should be conducted in order to reach conclusive screening policies for DS in older women.     

Effects of mid-trimester induced abortion on the subsequent pregnancy

The outcome of the pregnancy following (a) a mid-trimester termination of pregnancy (TOP) for fetal neural tube defect (NTD) (77 women=group 1); (b) mid-trimester TOP for fetal Down's syndrome (13 women=group 2); (c) delivery of a baby with NTD (119 women=group 3) was studied. The prenatal fetal loss was relatively high in all groups. In group 1 it was similar to that found in other studies after first trimester TOP, in group 2 it was associated with advanced maternal age and the unexpected finding in group 3 was not attributable to advanced maternal age. It is suggested that a previous NTD per se might increase the risk of fetal loss in the next pregnancy. A previous mid-trimester TOP for NTD was not associated with an increase in premature labour, small for dates babies or congenital abnormality in the next pregnancy, but there was a slight increase in the number of babies weighing less than 2500 g.     

Amniotic fluid-AFP in Down syndrome and other chromosome abnormalities

80·2 Per cent of 111 Down syndrome pregnancies had amniotic fluid (AF) alpha fetoprotein (AFP) levels on or below the median and 10·8 per cent at or below 0·5 MoM compared with 41·9 and 1·4 per cent of controls. These differences were even more striking when the gestational age was < 18 weeks compared with ⩾ 18 weeks. No such association was seen for other chromosome abnormalities including trisomy 18,45,X and mosaics, 47,XXY, 47,XXX, and other structural abnormalities and triploidy, even when high levels due to defects such as omphalocele and cystic hygroma were excluded. All cases of trisomy 13 and 80 per cent with 47,XYY had AF-AFP levels above the median. Selection of cases for karyotyping by a low level of AF-AFP would clearly fail to detect aneuploidies other than Down syndrome and is not recommended. A possible weak association between low maternal serum (MS) and AF-AFPs in Down syndrome was most evident at < 18 weeks, suggesting that MS screening between 16 and 18 weeks may be the most informative time.     

Accuracy of Down syndrome risks produced in a first-trimester screening programme incorporating fetal nuchal translucency thickness and maternal serum biochemistry

Over the past three years approximately 12 000 women have been screened in the first trimester through our OSCAR programme, which utilizes fetal NT and maternal serum free β-hCG and PAPP-A. During this time 30 cases of Down syndrome were identified either prenatally or postnatally. Using an established procedure the accuracy of predicted risk for Down syndrome was assessed in a population of 30 cases of Down syndrome and 11 758 unaffected pregnancies. The correlation between predicted risk and prevalence of Down syndrome was very high (r=0.9995). It is concluded that risks produced by the Fetal Medicine Foundation combined risk algorithm agree very closely with Down syndrome prevalence and can be used with confidence when counselling women of their risk. Copyright © 2002 John Wiley & Sons, Ltd.     

Risk of amniocentesis in women screened positive for Down syndrome with second trimester maternal serum markers

In routine obstetrical practice, prior to offering invasive prenatal diagnosis, it is crucial to weigh the risks attendant on amniocentesis against the individual's risk of aneuploidy. We took advantage of a policy of follow-up of patients undergoing Down syndrome maternal serum screening to compare the rates of fetal loss before 24 weeks and of early premature delivery at 24–28 weeks between women who underwent amniocentesis and women who did not. A total of 54 902 patients entered the study, of whom 4039 (7.35%) were lost to follow-up and 387 were excluded because of a severe fetal abnormality. Of the 50 476 remaining patients, 3472 had an amniocentesis whereas 47 004 had not and served as controls. In the amniocentesis group, the fetal loss rate before 24 weeks was 1.12% (95% CI=1.08–1.15) and the 24–28 weeks premature delivery rate was 0.40% (95% CI=0.39–0.41) which was significantly higher than in controls (0.42% with 95% CI 0.41–0.43 and 0.24% with 95% CI 0.23–0.25, respectively). The 0.86% difference in adverse outcome rates between the amniocentesis and control groups may be attributable to amniocentesis and compares favourably with the positive predictive value of maternal serum markers (1.70%) observed in the present study. Copyright © 2002 John Wiley & Sons, Ltd.     

Human chorionic gonadotropin levels in pregnancies with aneuploid fetuses

Maternal serum human chorionic gonadotropin (hCG) and the free alpha-hCG subunit were evaluated in 249 women from 9 to 11 weeks gestation who subsequently underwent chorionic villus sampling for determination of fetal karyotype and in 20 women of 18 or more weeks gestation who were ascertained to have an aneuploid fetus by genetic amniocentesis. Seven of the first-trimester pregnancies were determined to be aneuploid and six had hCG levels in the normal range (one triploid pregnancy had elevated hCG levels) whereas 12 of the 20 secondtrimester cases had abnormal hCG levels and an additional three had elevated levels of alpha-hCG. This study confirms the previous report of abnormal maternal serum hCG levels in women with an aneuploid fetus at ≥ 18 weeks gestation and demonstrates that hCG evaluation is not useful at 9–11 weeks gestation for selecting pregnancies at risk for fetal aneuploidy.     

Second-trimester levels of maternal urinary gonadotropin peptide in down syndrome pregnancy

Urinary gonadotropin peptide (UGP; β-core fragment), a major metabolite of human chorionic gonadotropin (hCG), was shown recently to be markedly elevated in Down syndrome pregnancy between 19 and 22 weeks of gestation. To confirm and extend this finding, we obtained maternal urine and matching maternal serum samples from 14 cases of Down syndrome and six other aneuploidies between 17 and 21 weeks of gestation. UGP was measured in all these samples and in 91 singleton control urines. Results were corrected for urinary creatinine level and expressed as multiples of the control median (MOM). hCG levels were assayed in all serum samples from the cases and compared with previously established reference values. The median UGP level in Down syndrome cases was 5.34 MOM (range 2.71–12.57); 88 per cent of the values were above the 95th centile of control levels after modelling. The median maternal serum hCG level for the same cases was 2.20 MOM (range 0.84–3.40); 36 per cent of the values were above the 95th centile. The level of UGP in every case including all other aneuploidies was higher than the comparable maternal serum hCG level. Elevated UGP measurements are strongly associated with fetal Down syndrome during the second trimester and could contribute to improved Down syndrome screening protocols that are more accessible and less expensive than are currently available.