A maternal serum screen for trisomy 18: an extension of maternal serum screening for Down syndrome.

The feasibility of extending second-trimester maternal blood screening for Down syndrome so as to include screening for trisomy 18 was examined using stored maternal serum samples collected for neural tube-defect screening. There were 12 samples from trisomy 18 pregnancies and 390 controls. The median maternal serum concentration of alpha-fetoprotein, free alpha-subunit human chorionic gonadotrophin, free beta-subunit human chorionic gonadotrophin, intact human chorionic gonadotrophin, total estriol, unconjugated estriol, estradiol, human placental lactogen, and progesterone were lowered in those pregnancies affected by trisomy 18 when compared with unaffected pregnancies matched for racial origin, maternal age, gestational age, and sample-storage duration. At an estimated odds risk of 1:400, 83.3% of affected pregnancies were detected using an algorithm which combines the maternal age-related risk with the maternal serum concentrations of unconjugated estriol, free alpha-subunit human chorionic gonadotrophin, free beta-subunit human chorionic gonadotrophin, estradiol, and human placental lactogen. The associated false-positive rate was 2.6%. At high risk odds of 1:10, the detection rate was 58.3%, with an associated false-positive rate of 0.3%. beta-Subunit human chorionic gonadotrophin and unconjugated estriol were the most powerful discriminators. It is possible to incorporate into existing Down syndrome screening programs an algorithm for detecting trisomy 18 with high sensitivity and specificity.     

Maternal serum screening for Down's syndrome in early pregnancy.

The possibility of improving the effectiveness of antenatal screening for Down''s syndrome by measuring human chorionic gonadotrophin concentrations in maternal serum during the second trimester to select women for diagnostic amniocentesis was examined. The median maternal serum human chorionic gonadotrophin concentration in 77 pregnancies associated with Down''s syndrome was twice the median concentration in 385 unaffected pregnancies matched for maternal age, gestational age, and duration of storage of the serum sample. Measuring human chorionic gonadotrophin in maternal serum was an effective screening test, giving a lower false positive rate (3%) at a 30% detection rate than that for maternal age (5%) and the two existing serum screening tests, unconjugated oestriol (7%) and alpha fetoprotein (11%). The most effective screening results were obtained with all four variables combined; at the same 30% detection rate the false positive rate declined to 0.5%. The new screening method would detect over 60% of affected pregnancies, more than double that achievable with the same amniocentesis rate in existing programmes (5%), and could reduce the number of children born with Down''s syndrome in the United Kingdom from about 900 a year to about 350 a year.     

Screening for Down's syndrome based on individual risk.

OBJECTIVE--To evaluate the effectiveness of biochemical screening of individual pregnancies for Down''s syndrome risk. DESIGN--Retrospective determination of risk. SETTING--Obstetric and cytogenetic services in Tayside, Scotland. SUBJECTS--3436 pregnant women who had screening for neural tube defects in the second trimester during November 1988 to March 1990 and whose pregnancies were dated by ultrasonography. Three women with pregnancies associated with Down''s syndrome reported later in 1990. MAIN OUTCOME MEASURES--Individual risk calculated from age at estimated date of delivery; chorionic gonadotrophin and alpha fetoprotein concentrations in serum samples obtained at precisely determined gestational ages in second trimester. Results of karyotype determination and outcome of pregnancy. RESULTS--During November 1988 to March 1990 karyotypes were determined for 5% of pregnancies for reasons of maternal age and genetic history and one of the eight affected fetuses was detected. Individual risk could not be calculated for 347 pregnancies, but screening on this basis would have detected five of the cases and required screening in 194 out of 3089 (6.3%) pregnancies; all three affected pregnancies reported later in 1990 would also have been detected, giving a success rate of 73% (95% confidence interval 39% to 94%). The age distribution of women according to individual risk suggests that women over 35 would be screened effectively. CONCLUSION--Screening based on individual risk would use resources more effectively than screening based on maternal age and genetic history without affecting detection rates in older women.     

Screening for Down's syndrome using serum alpha fetoprotein: a retrospective study indicating caution.

A report was made on the outcome of a four year retrospective study in 27 064 pregnancies, of the clinical efficiency, sensitivity, and specificity of a screening programme for Down''s syndrome based on reported strategies related to the measurement of maternal serum alpha fetoprotein. This study identified 27 pregnancies affected by Down''s syndrome with a median multiple of the median maternal serum alpha fetoprotein concentration of 0.82. This figure is considerably higher than that obtained from previous reports on this subject. With an age related multiple of the median maternal serum alpha fetoprotein strategy, 30.8% of Down''s affected pregnancies were identified as well as 11.6% of unaffected pregnancies. Perhaps a United Kingdom collaborative study should begin to investigate the reasons for such wide population variance in the reports for the median multiple of the median for Down''s affected pregnancies. Until such studies are carried out, screening for Down''s syndrome based on low maternal serum alpha fetoprotein concentration is premature.     

Risk assessment adjusted for gestational age in maternal serum screening for Down's syndrome.

OBJECTIVE--To investigate the relation between errors in calculation of gestational age and assessment of risk of Down''s syndrome and to analyse the implications for screening programmes. DESIGN--Retrospective analysis of dating of gestational age by menstrual history v ultrasound scan. Computer program with maternal age and concentrations of alpha fetoprotein and free beta human chorionic gonadotrophin to calculate risk for a range of expected dates of delivery. Computer simulated prospective application of new screening programme. SETTING--Teaching hospitals in Nottingham. SUBJECTS--31,561 women with singleton pregnancies with gestational age based on routine ultrasound scan. Computer simulation of 20,000 women in three age ranges (up to 37; up to 40; all). MAIN OUTCOME MEASURES--Distribution of error between gestational age based on ultrasound scan v menstrual history. Proportion of women in the population who require precise dating of pregnancy; proportion of women who require amniocentesis. RESULTS--With gestational age derived from ultrasound scan as reference the 95% confidence interval for gestational age by menstrual history was -27 to +9 days. A screening programme for Down''s syndrome for women up to age 40 would yield a low risk (< 1:250) for this range of days in 86.0% of cases. The 14.0% of women remaining would have one or more high risk values in their report and would thus require an ultrasound scan for precise dating of the pregnancy; 30% of these--that is, 3.7% of the screened population--would be identified as high risk and require consideration for amniocentesis. CONCLUSIONS--Screening programmes for Down''s syndrome require the facility for precise dating of pregnancy to improve the accuracy of risk assessment. This can be achieved without introducing additional scans for early dating in the whole population but by selecting only those cases (about 14%) when an error in dates is likely to affect the risk of Down''s syndrome.     

Predictive value of plasma human chorionic gonadotrophin beta subunit in diagnosing ectopic pregnancy after in vitro fertilisation and embryo transfer.

A study was conducted aimed at establishing a range of plasma concentrations of the beta subunit of human chorionic gonadotrophin that might predict ectopic pregnancy after in vitro fertilisation and embryo transfer. From May 1984 to February 1986, 161 consecutive pregnancies at the Monash University in vitro fertilisation unit were analysed by determining plasma beta human chorionic gonadotrophin concentrations between two and 10 weeks after oocyte collection. Eighty eight ongoing singleton pregnancies, 25 multiple pregnancies, 27 first trimester spontaneous abortions, 12 anembryonic pregnancies, and nine ectopic pregnancies resulted from these conception cycles. When compared with values for ongoing singleton pregnancies two weeks after oocyte collection plasma beta human chorionic gonadotrophin concentrations in ectopic pregnancies were significantly lower (p less than 0.05; Wilcoxon rank sum test). Two weeks after oocyte collection all plasma beta human chorionic gonadotrophin concentrations in the set of ectopic pregnancies were below 30.6 IU/l, which corresponded to the lower quartile (25th percentile) of beta human chorionic gonadotrophin concentrations in ongoing singleton pregnancies. The beta human chorionic gonadotrophin concentration corresponding to the lower quartile of ongoing singleton pregnancies at each week of gestation was used to derive the predictive value of various statistics in detecting ectopic pregnancy in patients after in vitro fertilisation. The sensitivity, specificity, predictive value of a positive result, predictive value of a negative result, and efficiency of a single plasma beta human chorionic gonadotrophin concentration in predicting ectopic pregnancy were 100%, 68.1%, 16.7%, 100%, and 70%, respectively, two weeks after oocyte collection. These results suggest that a single determination of the plasma beta human chorionic gonadotrophin concentration beginning 14 days after oocyte collection is clinically useful in predicting the outcome of pregnancy achieved by in vitro fertilisation. Ectopic pregnancy after in vitro fertilisation is more likely when beta human chorionic gonadotrophin concentration is below the lower quartile of values in ongoing singleton pregnancies achieved by the technique.     

Screening for aneuploidy in twin pregnancies: maternal age- and race-specific risk assessment between 9-14 weeks.

The aim of this study was to calculate the risk for aneuploidy in twin pregnancies between 9-14 weeks utilizing maternal age, race and dizygotic twinning rates. Using previously published risks for aneuploidy in singletons and twins at the time of amniocentesis and at term, we calculated new risk estimates for twins at 9-14 weeks gestation or at the time of chorionic villus sampling. Using these tables, the risk for trisomy 21 in at least one fetus of a twin gestation in a 32-year-old at 9-14 weeks is 1/285 for Whites and for African-Americans. This is equivalent to the risk for trisomy 21 (1/265) in a 35-year-old woman with a singleton at the same gestational age. The risks for trisomies 18 and 13 also follow similar trends. In counseling women with twin pregnancies at the time of first trimester nuchal translucency screening or chorionic villus sampling, it should be noted that the maternal age-related risk for aneuploidy for a 32-year-old is equivalent to that of a 35-year-old woman with a singleton gestation.     

Biochemical screening of fetal aneuploidies and neural tube defects by "double-test" in Croatia: a 10 years' experience

The aim of the study is to investigate the efficiency of the second-trimester biochemical screening, with maternal serum alpha-fetoprotein (MS-AFP) and free beta-subunit of human chorionic gonadotropin (free beta-hCG), during the ten-year period. The study included 11,292 of pregnant women between the 15th and 18th gestational week, who underwent screening from November 1996 to December 2006. The risk for trisomy 21 and trisomy 18 were calculated by computer software, based on a model which generated the final risk for fetal aneuploidies from the pregnant woman's a priori age risk and the likelihood ratio of the distribution of the biochemical markers, according to the second-trimester gestation. With the cut-off value of the final risk > or = 1:250, the detection rate for trisomy 21 was 75% (21/28). In women less than or equal to 35, the detection was 57.1% (8/14) and 92.9% (13/14) in those over 35 years, respectively. The detection rate of trisomy 18 was 50% (2/4). The results confirmed that the implementation of double-test, as non-invasive screening for fetal aneuploidies, should be accepted as a complementary method of antenatal care.     

Antenatal maternal serum screening for Down's syndrome: results of a demonstration project.

OBJECTIVES--To assess the implementation of antenatal screening for Down''s syndrome in practice, using individual risk estimates based on maternal age and the three serum markers: alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin. DESIGN--Demonstration project of Down''s syndrome screening; women with a risk estimate at term of 1 in 250 or greater were classified as "screen positive" and offered diagnostic amniocentesis. SETTING--Hospital and community antenatal clinics in four health districts in London. SUBJECTS--12,603 women of all ages with singleton pregnancies seen between February 1989 and the end of May 1991, with follow up of the outcome of pregnancy completed to the end of 1991. MAIN OUTCOME MEASURES--Uptake of screening, detection rate for Down''s syndrome, false positive rate, odds of being affected given a positive result, and uptake of amniocentesis in women with positive screening results, together with the costs of the screening programme. RESULTS--The uptake of screening was 74%. The detection rate was 48% (12/25), and the false positive rate was 4.1%, consistent with results expected from previous work based on observational studies. There was a loss of detection due to the selective use of ultrasound scans among women with positive screening results. One affected pregnancy occurred among 205 reclassified as negative; this illustrated the danger of false negatives occurring in this group and lends weight to the view that if an ultrasound estimate of gestational age is used it should be carried out routinely on all women rather than selectively among those with positive results. The estimated cost of avoiding the birth of a baby with Down''s syndrome was about 38,000 pounds, substantially less than the lifetime costs of care. CONCLUSION--Antenatal maternal serum screening for Down''s syndrome is effective in practice and can be readily integrated into routine antenatal care. It is cost effective and performs better than selection for amniocentesis on the basis of maternal age alone.     

Appraisal of a new scheme for prenatal screening for Down's syndrome.

OBJECTIVE--To appraise a new method of prenatal screening for Down''s syndrome based on maternal serum concentrations of alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin combined with maternal age--the "triple test." DESIGN--Examination of the cost effectiveness of the triple test relative to screening only by maternal age over a range of population detection rates. SETTING--Leicestershire Health Authority. MAIN OUTCOME MEASURES--Costs per affected fetus detected. RESULTS--The triple test is more cost effective than screening only by maternal age for risk cut off points for amniocentesis, resulting in a detection rate over 45%. The most efficient detection rate is around 60-65%, for which the cost per case detected is around 29,000 pounds, through screening with higher detection rates is still likely to be cost beneficial. CONCLUSIONS--Prenatal screening for Down''s syndrome based on the triple test should replace screening based only on maternal age. Individual women''s preferences should be elicited by the use of structured decision analysis in order to maximise utility and so increase the benefits of the screening programme.     

Significance of the maternal levels of serum alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol in various congenital developmental defects in pregnancy trimester II]

Maternal serum alpha-fetoprotein (MSAFP), human chorionic gonadotropin (hCG) and unconjugated oestriol (uE3) concentrations were measured in maternal serum samples from 21 pregnancies with neural-tube defects, 4 pregnancies with ventral wall defects (VWD) and 1662 unaffected pregnancies in women. These congenital malformations were confirmed by ultrasound scanning. The mean multiplate of the median (MoM) for AFP and uE3 was significantly different from the control values in cases of open NTD (AFP median MoM = 5.95, p < 0.001, uE3 median MoM = 0.2, p < 0.001), while hCG values did not differ from those of matched controls (hCG median MoM = 0.9). The biological basis of altered levels of uE3 in pregnancies with fetal NTDs is unclear.     

Triploidy in a fetus following amniocentesis referred for maternal serum screening test at second trimester

Amniocentesis was carried out at 17 weeks gestation in a 27-year-old woman, following an abnormal maternal serum screening (MSS) test. MSS test was carried out primarily to estimate the risk of trisomy for chromosome 21. The maternal serum markers used were alpha-fetoprotein (AFP), human chorionic gonadotrophin (hCG), and unconjugated estriol (uE3), together with maternal age. The fetus was identified as screen-positive for Edward's syndrome (trisomy 18), with low uE3, normal AFP and hCG levels. The calculated risk for trisomy 18 was more than 1:50. To identify any possible chromosomal abnormality, cytogenetic investigation was carried out on the amniotic fluid sample. The fetus's karyotype showed triploidy with 69, XXX chromosome complement in all the metaphase spreads obtained from three different cultures, using GTG banding technique. Upon termination of the fetus, gross abnormalities indicative of triploidy were present in the fetus.     

Screening for Down's syndrome in the North East Thames region.

The suggested strategies for a screening programme for Down''s syndrome by maternal serum alpha fetoprotein concentration were examined and tested on the experience of the North East Thames Regional. Screening by maternal serum alpha fetoprotein concentration may be used to identify pregnancies at increased risk, but this is useful only in women aged over 32 whose collective risk is greater than one in 200. The absolute probability of carrying babies with Down''s syndrome for individuals in this high risk group can then be calculated and used to decide whether further diagnosis by amniocentesis is desired.     

Prenatal fetal karyotyping and maternal serum alpha-fetoprotein screening.

Prenatal karyotyping was undertaken in 569 consecutive amniotic fluid samples where the indication for amniocentesis was two sequential raised maternal serum alpha-fetoprotein concentrations. In 475 successful cultures five chromosome abnormalities were found--four constitutional anomalies (47,XXY; 47,XYY; an inherited inv(8) (p23q11); and a de-novo translocation t(6;7) (p11;p22) and a culture-derived anomaly (trisomy 2) found in amniotic fluid cells but not in the fetus aborted because it had spina bifida. Of the pregnancies complicated by constitutional abnormalities, only the pregnancy in which the de-novo translocation was detected was terminated. No chromosome abnormalities were detected in the 17 pregnancies which miscarried after amniocentesis. These results provide little justification for including fetal karyotyping as an essential part of maternal serum alpha-fetoprotein screening programmes.     

Fetal nuchal translucency thickness

In the early 1990s Nicolaides introduced screening for trisomy 21 by fetal nuchal translucency thickness measurement with ultrasound between 11-13(+6) weeks. Already in 1866 L. Down noted that common features of patients with trisomy 21 are a skin being too large for the body and a flat face with a small nose. While detection rates for trisomy 21, given an invasive testing rate of 5%, were only 30% for screening by maternal age and 65% for screening by maternal serum triple test, the detection rate for screening by nuchal translucency combined with maternal age was 75% and this could be increased to 90% in combination with maternal serum screening (serum B-human chorionic gonadotropin and pregnancy-associated plasma protein-A) at 11-13(+6) weeks. The additional soft markers in the first trimester are the fetal nasal bone, the Doppler velocity waveform in the ductus venosus and tricuspid regurgitation and these markers can be used to further increase the detection rate of trisomy 21. In addition increased nuchal translucency thickness can also identify other chromosomal defects (mainly trisomy 13 and 18 and monosomy X) and major congenital malformations (mainly cardiac defects) and genetic syndromes.     

Maternal serum cell-free fetal DNA levels are increased in cases of trisomy 13 but not trisomy 18

Cell-free fetal DNA in the maternal circulation is a potential noninvasive marker for fetal aneuploidies. In previous studies with Y DNA as a fetal-specific marker, levels of circulating fetal DNA were shown to be elevated in women carrying trisomy 21 fetuses. The goal of this study was to determine whether cell-free fetal DNA levels in the serum of pregnant women carrying fetuses with trisomies 13 or 18 are also elevated. Archived maternal serum samples from five cases of male trisomy 13 and five cases of male trisomy 18 were studied. Each case was matched for fetal gender, gestational age, and duration of freezer storage to four or five control serum samples presumed to be euploid after newborn medical record review. Real-time quantitative polymerase chain reaction amplification of DYS1 was performed to measure the amount of male fetal DNA present. Unadjusted median serum fetal DNA concentrations were 97.5 GE/ml (genomic equivalents per milliliter; 29.2-187.0) for the trisomy 13 cases, 31.5 GE/ml (18.6-77.6) for the trisomy 18 cases, and 40.3 GE/ml (3.7-127.4) for the controls. Fetal DNA levels in trisomy 13 cases were significantly elevated ( P=0.016) by analysis of variance of the ranks of values within each matched set. In contrast, fetal DNA levels in trisomy 18 cases were no different from the controls ( P=0.244). Second trimester maternal serum analytes currently used in screening do not identify fetuses at high risk for trisomy 13. Fetal DNA may facilitate noninvasive screening for trisomy 13 provided that a gender-independent fetal DNA marker can be developed.     

1200例孕中期产前筛查结果的回顾性分析

目的：评价孕妇血清标记物（甲胎蛋白AFP、β-绒毛膜促性腺激素β-hCG和雌三醇uE3）的孕中期三联筛查在临床中的应用价值。方法：采用酶联免疫吸附法（ELISA）对1200例孕中期（14～22周）孕妇进行血清标记物AFP、β-hCG和uE3的检测,结合孕龄、孕周、体重等因素,经专门的筛查分析软件,计算唐氏综合征,18三体及神经管缺陷（NTD）的风险率。如孕妇为高风险,则进行胎儿的超声检查和染色体核型分析的产前诊断。结果：在1200例孕妇中,筛查高风险的孕妇有73例,其中唐氏综合征,18三体,NTD高风险孕妇分别为65例,5例和3例,假阳性率为6.08%（73/1200）。其中59例接受了产前诊断,占高风险孕妇的80.8%（59/73）。共检出1例唐氏综合征儿和1例无脑儿,未发现18三体,检出率为100%（2/2）,未有漏诊的情况。妊娠不良结局在筛查高风险组和低风险组的比率分别为17.1%和1.32%,两组有显著性差异（P〈0.01）。结论：利用孕妇血清标记物（AFP、β-hCG和uE3）的孕中期无创伤性产前筛查,结合产前诊断,对减少出生缺陷儿的出生,具有重要意义,并且高风险的筛查结果对胎儿的预后有一定的提示作用。     

Lessons from 1950

Second-trimester maternal serum screening is a noninvasive means of identifying pregnant women at an increased risk for various conditions including a fetus with open spina bifida, fetal Down syndrome, trisomy 18, multiple gestation, and adverse pregnancy outcome. Combinations of several different markers are available for screening. These include alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. In this review, we discuss the benefits and limitations of the screening tests and the suggested protocols for the care of patients.     

Maternal Serum α-Fetoprotein Screening for the Detection of Neural Tube Defects—Report of a Pilot Program

We tested 10,715 low-risk pregnancies in a voluntary maternal serum α-fetoprotein screening program for the detection of neural tube defects in California. In all, 5.3 percent of women had one elevated serum level, 3.3 percent were referred for sonography and 1.5 percent for amniocentesis. There were 12 cases of open neural tube defects (1.1 per 1,000); all of the mothers had one elevated serum αfetoprotein level: nine (75 percent) completed the protocol and the neural tube defects were correctly identified. No normal pregnancies were terminated. The risk of an open neural tube defect occurring was about 1 in 50 after the first abnormal serum level and 1 in 15 at amniocentesis. We found significantly increased risk for fetal death and low birth weight after one elevated serum α-fetoprotein level, though the likelihood of a normal pregnancy outcome was about 80 percent. Maternal serum screening was also useful in identifying twin pregnancies and correcting underestimated gestational dates.     

Contribution of ultrasonographic examination to the prenatal detection of trisomy 21: experience from 19 European registers

The objective of this study was to evaluate the contribution of ultrasound scanning to the prenatal detection of trisomy 21 in a large unselected European population. Data from 19 congenital malformation registers in 11 European countries were included. The prenatal ultrasound screening programs in the countries ranged from no routine screening to three ultrasound investigations per patient. Routine serum screening was offered in four of the 11 countries and routine screening on the basis of maternal age amniocentesis in all. The results show that overall 53% of cases of trisomy 21 were detected prenatally with a range from 3% in Lithuania to 88% in Paris. Ninety-eight percent of women whose babies were diagnosed before 24 weeks gestation chose to terminate the pregnancy. Centres/countries that offer serum screening do not have a significantly higher detection rate of trisomy 21 when compared to those that offer maternal age amniocentesis and anomaly scanning only. Fifty percent of trisomy 21 cases were born to women aged 35 years or more. In conclusions, second trimester ultrasound plays an important role in the prenatal diagnosis of trisomy 21. Of those cases prenatally diagnosed, 64% of cases in women <35 years and 36% of those in women >or=35 years were detected because of an ultrasound finding. Ultrasound soft markers accounted for 84% of the scan diagnoses. There is evidence of increasing maternal age across Europe with 50% of cases of trisomy 21 born to women aged 35 years or more.