Trisomy 18 and maternal serum and amniotic fluid alpha-fetoprotein

Maternal serum and amniotic fluid alpha-fetoprotein levels were studied retrospectively in a total of 58 pregnancies with trisomy 18. In those pregnancies uncomplicated by either fetal exomphalos or neural tube defect the midtrimester maternal serum alpha-fetoprotein (MSAFP) levels were markedly reduced, the median value for 38 such pregnancies being 0.6 multiples of the median (MoM). Trisomy 18 with exomphalos was associated with a higher median MSAFP, but still within the normal range: 1.1 MoM, (nine pregnancies); trisomy 18 with exomphalos and neural tube defect (NTD) was associated with grossly raised levels: median MSAFP was 4-5 MoM (three pregnancies). Amniotic fluid alpha-fetoprotein (AFAFP) levels were normal in uncomplicated trisomy 18 pregnancies: median AFAFP, for 19 pregnancies, was 1.1 MoM. Exomphalos alone, or together with neural tube defect, was associated with greatly elevated levels of AFAFP; for exomphalos alone median AFAFP was 9.59 MoM (four pregnancies), and for exomphalos with neural tube defect the median AFAFP was 23.95 Mom (three pregnancies). Screening with low and high MSAFP, routine ultrasound, and amniocentesis on all women aged 35 years or over, together might identify over 50 per cent of pregnancies with trisomy 18.     

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.     

Amniotic fluid fibrinolytic system in fetal neural tube defects

Second trimester amniotic fluid fibrinolytic system was examined in normal pregnancies and those complicated by anencephaly, spina bifida and fetal chromosome abnormalities. No significant difference was demonstrated between the fibrinolytic systems from normal pregnancies and those complicated by fetal chromosome abnormalities. In pregnancies complicated with anencephaly and spina bifida no significant difference was demonstrated for alpha-1-antitrypsin, alpha-1-antichymotrypsin and urokinase. Plasminogen was significantly lower (p < 0.02) and plasmin significantly higher (p < 0.001) than levels from normal amniotic fluid. Alpha-2-macroglobulin, fibrinogen, FDP-D and FDP-E were detected only in pregnancies complicated with anencephaly and spina bifida.     

Prenatal screening for Down syndrome in twin pregnancies: Estimates of screening performance based on 61 affected and 7302 unaffected twin pregnancies

The aims of this study were to determine whether assumptions used in prenatal screening for Down syndrome in twin pregnancies are valid and derive estimates of risk and screening performance in twin pregnancies using observed data. Data were collected on nuchal translucency, chorionicity, pregnancy associated plasma protein-A (PAPP-A), and free ß human chorionic gonadotrophin (free ß-hCG) from 61 twin pregnancies with Down syndrome and 7302 unaffected twin pregnancies. Distribution parameters were determined and used to estimate screening performance. The assumption that proportional differences in serum marker levels in affected and unaffected singleton pregnancies apply to twin pregnancies was not confirmed. Median free β-hCG value in monochorionic affected twin pregnancies (2.63 multiples of the median [MoM]; 95% CI, 1.79-3.22 MoM) was lower than that assuming proportionality (3.76 MoM), and the median PAPP-A value in dichorionic affected twin pregnancies (1.88 MoM; 95% CI, 1.60-2.17 MoM) was higher than that based on proportionality (1.33 MoM). The detection rate was 87% for a 3% false-positive rate in monochorionic twin pregnancies and 74% in dichorionic twin pregnancies compared with 86% in singleton pregnancies. Estimates of screening performance in Down syndrome twin pregnancies do not need to rely on assumptions and can take account of chorionicity and gestational age.     

Genetic amniocentesis in biamniotic twin pregnancies by a single transabdominal insertion of the needle

We present a technique to aspirate amniotic fluid from both sacs in biamniotic twin pregnancies using a single abdominal insertion with a spinal needle. It was successful in 48 out of 55 cases of biamniotic twin pregnancies referred to our perinatal unit between 1985 and 1994. The single insertion technique was used when the inter-amniotic membrane was clearly evident and two separate free amniotic fluid pools could be reached by the operator with a single puncture. An adequate amount of amniotic fluid was sampled from both sacs to make a cytogenetic diagnosis in all cases. There were four fetuses with trisomy 21 in three twin pregnancies. In two cases, only one twin was affected whilst the co-twin was normal, so that a selective feticide was performed. No miscarriages due to genetic amniocentesis were reported. After 1990, all genetic amniocenteses in biamniotic twin pregnancies (except for one case due to late booking) were performed between 14 and 15 weeks of gestation and with all cases except one, it was possible to sample both twins by a single puncture. We suggest that early amniocentesis (14–15 weeks) by a single abdominal puncture could be a reliable and safe alternative to first-trimester chorionic villus sampling in twin pregnancies.     

Maternal serum levels of total activin-A in first-trimester trisomy 21 pregnancies

Maternal serum total activin-A concentration was measured in 45 pregnancies affected by trisomy 21 and 493 control unaffected pregnancies at 10–14 weeks of gestation. In the trisomy 21 pregnancies total activin-A concentration was significantly higher (1.36 MoM of the unaffected pregnancies) and in 16% of cases the level was above the 95th centile of normal. The log₁₀ SD for the control group and the trisomy 21 group were 0.17 and 0.22, respectively. The median pregnancy associated plasma protein-A (PAPP-A) in this trisomy 21 series was 0.49 and for free β-hCG was 2.05. In the trisomy group there were significant positive associations between total activin-A and PAPP-A (0.6071) and free β-hCG (0.4255). The low median difference and the high overlap in values between trisomic and unaffected pregnancies make total activin-A of little practical use in first-trimester screening for trisomy 21. Copyright © 2001 John Wiley & Sons, Ltd.     

The time of appearance and disappearance of fetal DNA from the maternal circulation

A single copy Y-chromosome DNA sequence was amplified using the polymerase chain reaction (PCR) from the peripheral blood of 30 women who had achieved a pregnancy through an in vitro fertilization (IVF) programme. The time of conception was known precisely and was confirmed by serial ultrasound scans. Conceptions were dated as the number of weeks after fertilization plus 2, to give a time equivalent to the obstetric menstrual dating of the pregnancy (LMP). Y-chromosome-specific DNA was detected in all pregnancies with a male fetus (18/30). The earliest detection was at 4 weeks and 5 days, and the latest at 7 weeks and 1 day. Y-chromosome-specific sequences were no longer detected in any of the male pregnancies 8 weeks after delivery. No Y-chromosome sequences were detected in any of the pregnancies where only female babies were delivered. This demonstrates that fetal DNA appears in the maternal circulation early in the first trimester, that it can be identified in all pregnancies tested by 7 weeks, that it continues to be present throughout pregnancy, and that it has been cleared from the maternal circulation 2 months after parturition. Early non-invasive prenatal diagnosis for aneuploidies and inherited disorders will be possible in all pregnancies if fetal cells can be isolated free from maternal contamination (or identified accurately in the presence of maternal cells) without problems of contamination from previous pregnancies.     

Increased risk of abortion after genetic amniocentesis in twin pregnancies

Forty-seven twin pregnancies among 3676 patients who had a genetic amniocentesis between 1973 and 1979, are reported. The detection rate of twins at the time of amniocentesis was 62 per cent. Five (17 per cent) of the 29 women with detected twin pregnancy aborted spontaneously, these are compared with 1 (6 per cent) of 18 women with undetected twin pregnancies and with 3 (3 per cent) of 93 singleton pregnancies, selected as controls as they had amniocentesis performed immediately before and after each of the twin mothers. Two of 9 (22 per cent) twin pregnancies, who had at least two punctures in at least one sac aborted, while 3 of 20 twin pregnancies with one puncture in each sac aborted (15 per cent). One of 18 (6 per cent) twin pregnancies, where only one sac was punctured, because the twin pregnancies were undetected, aborted. Amniocentesis of both sacs in twin pregnancies seems associated with an increased risk of spontaneous abortion. The indications for amniocentesis in twin pregnancies should be critically evaluated.     

Prenatal diagnosis of spina bifida aperta after first-trimester valproate exposure

In the context of a prospective study on the adverse effects of anti-epileptic drugs on fetal outcome, we evaluated our experience with prenatal diagnosis by ultrasonography and α- fetoprotein (AFP) determination in amniotic fluid. We compared these results with AFP values in maternal serum obtained prior to amniocentesis. From November 1985 to July 1990, amniocentesis at 16–18 weeks of gestation was performed in 267 pregnancies of 237 different women using anti-epileptic drugs. Among 92 pregnancies with maternal valproic acid use, five (including one concordantly affected monozygotic twin-pair) were terminated because of a spina bifida aperta, all prenatally diagnosed by AFP determination and acetylcholinesterase electrophoresis in amniotic fluid. The maternal serum AFP level was raised (⩾ 2.5 multiples of the median (MOM) for singleton pregnancies and ⩾ 4.5 MOM for twin pregnancies) in only two of these five affected pregnancies. We emphasize that maternal serum AFP levels may be unreliable for prenatal screening for fetal neural tube defects in women taking valproate and recommend that amniocentesis and fetal ultrasound examination should be offered directly.     

Is placental mosaicism associated with poor perinatal outcome?

In 37 pregnancies with placental mosaicism detected at first-trimester chorionic villus sampling in 2000 pregnancies, two pregnancies (5.4 per cent) ended in a spontaneous abortion at 15 weeks (46,XX/47,XX, + 16) and in a perinatal loss in a term pregnancy (46,XY/ 47,XY, +10), respectively. The outcome of the other 35 pregnancies was normal. The total pregnancy loss rate before 28 weeks in the first 1000 pregnancies was previously reported to be 3.6 per cent.     

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.     

First-trimester maternal serum human thyroid-stimulating hormone in chromosomally normal and Down syndrome pregnancies

Maternal serum human thyroid-stimulating hormone (TSH) levels were investigated in chromosomally normal and Down syndrome pregnancies to determine whether TSH can be used as a marker for Down syndrome in the first trimester. Measurements were conducted on stored serum samples collected from 23 Down syndrome pregnancies and 115 unaffected pregnancies before chorionic villus sampling (CVS), between 9 and 11 completed weeks of pregnancy. The samples were matched for gestational age, maternal age, maternal weight and duration of storage of the serum sample. Maternal TSH concentration was slightly decreased in Down syndrome pregnancies, with a median of 0.84 multiples of the median (MoM). Maternal serum human chorionic gonadotropin (hCG) concentration was slightly elevated in Down syndrome pregnancies, with a median of 1.03 MoM. Both differences were not significant applying matched rank analysis (p=0.50 for TSH and p=0.43 for hCG). The association between TSH and hCG in unaffected pregnancies was also measured. The Spearman correlation coefficient between TSH and hCG was −0.21 which was statistically significant (p=0.02, 95% confidence interval −0.38 to −0.03). However, it was concluded that TSH is not a useful marker for distinguishing Down syndrome-affected pregnancies from normal pregnancies in the first trimester. Copyright © 2001 John Wiley & Sons, Ltd.     

Ultrasound evaluation of pregnancies at risk for homozygous α-thalassaemia-1

Twenty-six pregnant Chinese women who were at risk of giving birth to a fetus affected with homozygous α-thalassaemia-1 were examined serially by ultrasound. Six of these 26 pregnancies were affected. In one third of the affected pregnancies progressive fetal ascites appeared before 24 weeks gestation and these pregnancies were terminated. In the remaining two thirds abnormal estimated fetal weight-placental volume (EFW-PV) ratio and fetal growth retardation as evidenced by a falling biparietal diameter (BPD), femur length (FL) but a normal abdominal circumference (AC) was apparent by 28 weeks gestation. Increased transverse cardiac (TC) diameter was another consistent finding but appeared late. All these features appeared before the onset of fetal ascites. A normal EFW-PV ratio and fetal growth until 28 weeks gestation was a reassuring sign of normality. Abnormal EFW-PV ratio was the earliest sign to appear in affected pregnancies and a normal ratio until 28 weeks gestation had a 100 per cent predictive value.     

Improved parameters for risk estimation in Down's syndrome screening

A new method is described for calculating maternal serum marker distribution parameters which will improve risk estimation when screening for Down's syndrome. The approach is to calculate parameters using data from the local screened population and data obtained by meta-analysis from all published studies. The local data are used to derive the variance and covariance in unaffected pregnancies. The meta-analysis is used for the mean level in Down's syndrome pregnancies together with the differences in variance and covariance between affected and unaffected pregnancies. Forty-four published studies were analysed. The mean level for Down's syndrome in multiples of the normal median was 0·73 for alpha-fetoprotein (AFP) in total of 1140 pregnancies, 0·73 for unconjugated oestriol (uE₃) in 613, 2·02 for human chorionic gonadotropin (hCG) in 850, and 2·30 for free β-hCG in 477. For all four markers, the variance in Down's syndrome was higher than in unaffected pregnancies; for AFP and uE₃, the covariances were also higher in Down's syndrome, but for the other markers they were lower. The method was illustrated using data from 6387 pregnancies screened in Leeds.     

First trimester screening for Down syndrome and assisted reproduction: no basis for concern

In pregnancies obtained after assisted reproduction the false-positive rate of second trimester Down syndrome (DS) screening is increased by 1.5–3-fold. This may cause an increase in the number of amniocenteses and the fetal loss rate. The present study for the first time examined whether assisted reproductive technologies affect the results of first trimester screening. The markers PAPP-A, free β-hCG and the nuchal translucency (NT) thickness were examined at 12–14 weeks' gestation. Screening markers in 47 in vitro fertilisation (IVF), 63 ovulation induction (OI) and 3026 spontaneously conceived singleton pregnancies were compared. The MoM (multiples of the median) value in the IVF pregnancies was 1.02 (95% CI: 0.85–1.22) for PAPP-A, 1.14 (95% CI: 0.95–1.37) for β-hCG and 0.97 (95% CI: 0.89–1.05) for NT; the MoM value in the OI pregnancies was 0.89 (95% CI: 0.76–1.05) for PAPP-A, 1.08 (95% CI: 0.93–1.25) for β-hCG and 1.02 (95% CI: 0.95–1.11) for NT. The first trimester marker values in assisted reproductive pregnancies and spontaneously conceived pregnancies were not significantly different. Estimated false-positive rates for a risk cut-off of 1:400 varied from 4.7% in IVF pregnancies to 5.1% in OI pregnancies. Therefore the false-positive rate in Down syndrome screening should be independent of the method of conception. Copyright © 2001 John Wiley & Sons, Ltd.     

Abnormal amniotic fluid levels of CA 125 in second-trimester Down syndrome pregnancies

The aim of this study was to evaluate the concentration of CA 125 in second trimester amniotic fluid from Down syndrome pregnancies. CA 125 was measured in stored amniotic fluid samples from pregnancies of 14–19 weeks' gestation with and without Down syndrome fetuses. CA 125 levels were expressed in multiples of the median (MOM) for normal pregnancies of the same gestational age. Twenty-one pregnancies with Down syndrome fetuses and 63 unaffected controls matched for maternal age, gestational age, and duration of storage were studied. The median MOM values of the affected pregnancies were significantly higher than those of the controls (1·41 MOM versus 0·99 MOM). These findings show that there is an increased concentration of CA 125 in second-trimester amniotic fluid from Down syndrome pregnancies.     

Maternal serum leptin concentration during the second trimester of pregnancy: association with fetal chromosomal abnormalities

Recent studies suggest that leptin, the product of the obese gene, is produced by the placenta during pregnancy. The present study addressed the question whether second trimester maternal serum leptin could be altered by fetal Down syndrome or Edwards syndrome. Maternal serum leptin concentrations were measured in 18 pregnancies complicated with Down syndrome, six pregnancies complicated with Edwards syndrome and 183 uncomplicated pregnancies during the second trimester of pregnancy. The present results demonstrate that leptin concentrations in uncomplicated pregnancies slightly decrease from the 16th week of pregnancy, reaching a minimum of 18.8 ng/ml around the 20th week, and then rapidly increase to 28.2 ng/ml by the 24th week. Leptin correlation with maternal body weight decreases from r=0.695 at 16–17 week of gestation to r=0.544 at >22 weeks of gestation. There was no significant difference between the mean MoMs of Down syndrome- (0.926) or Edwards syndrome- (0.960) affected pregnancies and normal pregnancies (1.002). A weak correlation (r=0.18, p<0.02) was observed between corrected leptin MoMs and human chorionic gonadotrophin (hCG) MoMs in normal pregnancies. It is assumed that around the 20th week of pregnancy placental leptin production is activated or at least is accelerated and it is added to the amount of leptin produced by maternal adipose tissue. Fetal Down syndrome or Edwards syndrome does not seem to alter maternal leptin concentration and therefore leptin cannot be used as a marker for these chromosomal abnormalities in the early second trimester of pregnancy. Copyright © 2002 John Wiley & Sons, Ltd.     

Menkes X-linked disease: Prenatal diagnosis of hemizygous males and heterozygous females

Menkes X-linked disease, a copper disturbance syndrome, is detectable in cell cultures. Prenatal findings in two at-risk foetuses suggested that prenatal diagnosis was also feasible. In this study, we report substantial evidence that therapeutic abortion can be limited to hemizygous males. Forty-two at-risk pregnancies from 21 European families and 1 Canadian family were monitored with ⁶⁴Cu-uptake into cultured amniotic fluid cells. In 10 pregnancies with a male karyotype an affected foetus was predicted on the basis of the copper studies. The pregnancies were terminated and the diagnosis was in each case confirmed by a markedly increased placenta copper content. Fourteen male foetuses were predicted to be unaffected and none of them has developed signs of Menkes disease after birth. In 6 of these cases the diagnosis was checked in the newborn boy by placenta copper measurements, and they all had copper concentrations within normal limits. Eighteen pregnancies with a female karyotype were also studied. 9 females could be identified as carriers on the basis of the tissue culture studies or raised placenta copper values.     

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.     

Preterm delivery rate and fetal outcome in structurally affected twin pregnancies: A retrospective matched control study

Data from 23 twin pregnancies with one structurally affected fetus were compared with data from 23 twin pregnancies with proven absence of structural fetal anomalies and matched for maternal age, parity, and year of delivery. The preterm delivery rate ( < 37 weeks) was high in both groups but not significantly different (57 vs. 48 per cent). Perinatal mortality was significantly higher in the structurally affected twin pregnancies (65 vs. 9 per cent). In the affected twins, birth weight of the anomalous fetus was significantly lower than that of the normal co-twin. Since there was no difference in the incidence of maternal disease (hypertensive disorders, diabetes), it was concluded that the higher perinatal mortality was determined mainly by the nature of the anomaly and not by the preterm delivery rate.