Maternal serum unconjugated oestriol and human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome

OBJECTIVE

To investigate maternal serum unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in twin pregnancies and to consider the implications of the results for antenatal screening for Down's syndrome.

DESIGN

Measurement of maternal serum uE3 and hCG levels from 15-22 weeks of gestation in twin and singleton pregnancies. Previously available maternal serum alpha-fetoprotein (AFP) levels were also presented.

SETTING

Stored serum samples collected from women receiving routine antenatal care in Oxford were used.

SUBJECTS

200 women with a twin pregnancy and, for each, three singleton control pregnancies matched for gestational age (same completed week of pregnancy) and duration of storage of the serum sample (same calendar quarter).

RESULTS

The median uE3, hCG and AFP levels in the twin pregnancies were respectively, 1.67 (95% CI 1.56-1.79), 1.84 (95% CI 1.64-2.07) and 2.13 (95% CI 1.97-2.31) multiples of the median (MoM) for singleton pregnancies at the same gestational age. The variance of values for the three serum markers (expressed in logarithms), and the correlation coefficients between any two, were similar in the twin and singleton pregnancies.

CONCLUSION

In maternal serum screening programmes for Down's syndrome dividing uE3, hCG and AFP MoM values in twin pregnancies by the corresponding medians for twin pregnancies will, in expectation, yield a similar false-positive rate in twin pregnancies as in singleton pregnancies.

Breast cancer screening by mammography: an overview

Given the differences between the nine studies in design and execution alone, it is remarkable that they all support the same general conclusion that mammographic screening for breast cancer is capable of reducing mortality from the disease. There are also differences between them in the screening technique (age range, interval between screens, number of mammographic views) and treatment but this does not provide a simple guide to what we can expect in the National Health Service Breast Cancer Screening Programme which is now underway in this country. The new national programme recruits women in the age range 50-64 and Table 3 shows the result from five of the studies in which separate data for a 'middle-age' group can be derived: the total Utrecht study group was aged 50-69 and the other three cannot be divided in this way. In each study, apart from the HIP study, the magnitude of the benefit is greater than in the total group. It is possible that these differences will decrease with longer follow-up (it took longer for an effect to emerge in the youngest age group in the HIP study) but the relative risks in Table 3 give a better guide than those in Table 2 in the short term. The specific effects of different intervals between screens and mammographic views are currently being investigated in randomized clinical trials. In the meantime our best estimate of what is likely to happen in the national programme is probably provided by the two-counties study which, like us, used single-view mammography and in the 50-64 age group had an average screening interval of 33 months-close to the 3 years we have adopted.

Birth prevalence of Down's syndrome in England and Wales

The natural birth prevalence of Down's syndrome for England and Wales in 1974-1987 (i.e., the birth prevalence in the absence of prenatal diagnosis and the induced abortion of affected pregnancies) was estimated by applying the maternal age-specific birth prevalence derived from epidemiological studies to the number of births in single-year age groups tabulated by the Office of Population Censuses and Surveys (OPCS). On average, the natural birth prevalence was 12.6 per 10,000 births and increased slightly from 12.2 to 13.2 per 10,000 births over the 14-year period. Using data on induced abortions carried out on account of Down's syndrome reported to OPCS under the statutory abortion notification scheme, 14 per cent of affected births were avoided by the induced abortion of affected pregnancies, so that the actual birth prevalence of Down's syndrome was estimated at 10.8 per 10,000 births. Using data on Down's syndrome births reported to OPCS under the voluntary congenital malformation notification scheme, the prevalence was 7.2 per 10,000 births, so only 67 per cent of the estimated number of affected births were, in fact, notified to the scheme.

Maternal serum alpha-fetoprotein screening for open neural tube defects in twin pregnancies

Data on maternal serum alpha-fetoprotein (AFP) levels at 13-24 weeks' gestation in 46 twin pregnancies with open neural tube defects (22 with anencephaly, 24 with open spina bifida) and 169 unaffected twins were used to estimate the detection and false-positive rates associated with different cut-off levels. Using the conventional cut-off level of 2.5 multiples of the median (MoM) for unaffected singleton pregnancies of the same gestation and laboratory, the detection rate in twins was 99 per cent for anencephaly and 89 per cent for open spina bifida, with a false-positive rate of 30 per cent. Using a 5.0 MoM cut-off level to maintain a similar false-positive rate to that found among singleton pregnancies at 16-18 weeks' gestation (about 3 per cent), the detection rate was 83 per cent for anencephaly and 39 per cent for open spina bifida. Estimates are provided of the odds of having an affected twin pregnancy given a positive AFP result as well as the odds for individual women with a raised AFP level.

Ultrasound fetal femur length measurement in the screening for Down's syndrome

The fetal femur length determined by an ultrasound examination at between 13 and 39 weeks gestation in 83 pregnancies associated with Down's syndrome was statistically significantly less than the expected value for pregnancies with the same biparietal diameter examined in the same ultrasound department (P less than 0.0001). Expected values were based on linear regressions of femur length on biparietal diameter in 1340 control pregnancies from 27 ultrasound departments. The median value for the affected pregnancies was 0.94 times the expected value (95% CI 0.92 to 0.97). Eleven per cent of affected and 1.4% of control pregnancies had values less than or equal to 0.85 times the expected. The reduction in femur length in affected pregnancies was not related to biparietal diameter or to maternal age. Fetal femur length may be useful as an ancillary screening variable in the antenatal screening for Down's syndrome.

Amniotic fluid acetylcholinesterase measurement in the prenatal diagnosis of open neural tube defects. Second report of the Collaborative Acetylcholinesterase Study

Seventeen centres from Australia, Britain, France, and the United States collaborated in a study to compare amniotic fluid acetylcholinesterase (AChE) determination by gel electrophoresis and amniotic fluid alpha-fetoprotein (AFP) measurement as diagnostic tests for open neural tube defects. The study was based on 32,642 women with singleton pregnancies (including 428 with open spina bifida and 238 with anencephaly) who had an amniocentesis at 13-24 weeks' gestation. The AChE test yielded a detection rate for open spina bifida of 99 per cent (95 per cent confidence interval 98-100 per cent), 98 per cent for anencephaly (95 per cent confidence interval 96-100 per cent), and a false-positive rate of 0.34 per cent (95 per cent confidence interval 0.28-0.40 per cent) excluding miscarriages, intrauterine death, and serious fetal abnormalities. The false-positive rate was 0.30 per cent among the 13 centres that used a specific AChE inhibitor in the test. Comparable rates for the AFP test were less favourable. (For example, the open spina bifida detection rate was 90 per cent and the false-positive rate was 0.46 per cent using the cut-off levels specified in the U.K. Collaborative AFP Study.) The AChE false-positive rate was lower in samples that were not bloodstained (0.16 per cent) than in those that were (2.4 per cent). It was higher in women who had an amniocentesis on account of a raised maternal serum AFP level (0.56 per cent) than in those who had one for other reasons (0.29 per cent). The best results were obtained by a combination of the two tests, an effective and economical policy being to perform the AFP measurement on all amniotic fluid samples and an AChE test on samples with AFP levels greater than or equal to 2.0 multiples of the normal median (about 5 per cent of all samples). Using this policy, the open spina bifida detection rate was 96 per cent and the false-positive rate was 0.14 per cent (0.06 per cent for samples that were not bloodstained and 1.2 per cent for those that were; 0.40 per cent for women with raised serum AFP levels and 0.09 per cent for other women). This policy offers a useful improvement to the prenatal diagnosis of open spina bifida.

AFP and age screening for Down syndrome

The availability of maternal serum alpha-fetoprotein (AFP) values from neural tube defect screening programmes offers the opportunity to improve the effectiveness of screening for Down syndrome. By appropriately combining information on maternal serum AFP and maternal age fewer women would need an amniocentesis to detect a given number of Down syndrome pregnancies or, for a given number of women having amniocentesis, more cases of Down syndrome would be detected than if age alone were used. For example to detect 40% of pregnancies with Down syndrome using AFP and age, 7% of women would need an amniocentesis compared with 11% using age alone. If an amniocentesis and a chromosome analysis together cost $1,000 this is equivalent to a saving of $37,000 per 1000 women screened. The use of AFP as well as age in Down syndrome screening allows patients to be better informed of their risk of having an affected pregnancy. For example, a 35-year-old woman has a risk of a Down syndrome term pregnancy of about 1:380, the risk is 1:120 if the AFP level is 0.40 multiples of the normal median (MoM) and 1:1800 if it is 2.50 MoM. Software providing computer assisted test interpretation has been produced to facilitate the estimation of risk and to identify women with positive screening results.

Maternal serum thyroid antibodies in early pregnancy and fetal Down's syndrome

Thyroid antibodies were measured in mid-trimester antenatal serum samples from 77 pregnancies affected by fetal Down's syndrome and 385 unaffected control pregnancies. Using a haemagglutination technique, thyroglobulin antibodies were detected in 5.2 per cent of cases (4) and 2.9 per cent of controls (11), and thyroid microsomal antibodies were detected in 22 per cent (17) and 15 per cent (59), respectively. Using an enzyme-linked immunosorbent assay (ELISA) for thyroglobulin antibodies and a cut-off level of 50 KIU/l, positive results were found in 25 per cent of cases (19) and 22 per cent of controls (84). Using an ELISA for thyroid microsomal antibodies and the same cut-off level, the proportions were 52 per cent (40) and 39 per cent (149), respectively. While not statistically significant, the differences were consistent with the previously reported increased levels of thyroid antibody found in non-pregnant women who had had pregnancies associated with Down's syndrome.

A nationwide study of breast disease

Records of histopathology from the 3734 Jewish women having breast biopsy and/or operations in all Israeli hospitals during the year from July 1979 to June 1980 were reviewed. Approximately 28.5% of these women were diagnosed as having breast cancer and 71.5% as having benign breast disease: 48.5% had benign proliferative mastopathy (BPM), 16.6% had fibroadenoma (FA) without coexistent BPM, and 6.4% had other benign breast conditions. The age-specific incidence rate was 66 in 100,000 for breast cancer and 165.2 in 100,000 for benign breast disease. Native European or American women and native Israeli women had significantly higher age standardized incidence rates of both breast cancer and BPM, but not of FA, as compared to African/Asian-born women (P less than 0.01). Age-related ratios between invasive to precursor breast lesions were similar in all ethnic groups. The data suggest that breast cancer and benign proliferative mastopathy may have a common etiologic component.

The impact of screening for open neural tube defects in England and Wales

Using information derived from the voluntary system of notification of congenital malformations in England and Wales, the birth prevalence of anencephaly and spina bifida was estimated to have declined by 80 per cent from 31.5 to 6.2 per 10,000 between 1964-1972 and 1985. Over the same period, notified terminations of pregnancy with a suspected fetal central nervous system abnormality increased from less than 1 per cent to 56 per cent of neural tube defect births and central nervous system terminations combined, accounting for 31 per cent of the decline in births. Routinely collected national statistics provide a method for monitoring the impact of screening for open neural tube defects. However because they are incomplete and lack detail an alternative method of monitoring is needed. This paper includes an outline of such a method, together with the results of a pilot study designed to assess the feasibility of monitoring screening in the Oxford Region.

Effect of estimating gestational age by ultrasound cephalometry on the specificity of alpha-fetoprotein screening for open neural-tube defects

A total of 1268 women had a maternal serum alpha-fetoprotein (AFP) screening test for open neural-tube defects between 15 and 22 weeks gestation and a routine ultrasound examination at their first antenatal visit. All had a singleton infant without a neural-tube defect. AFP values were expressed as multiples of the normal median at the relevant gestational age (MoM). The percentage of women with raised maternal serum AFP levels was less when gestation was estimated by the fetal biparietal diameter (BPD) than when the time since the first day of the last menstrual period (LMP) was used; 1.8% compared with 2.3% at a serum AFP cut-off level of 2.5 MoM. Different ultrasound policies were compared for their effect on AFP screening and the best was found to be routine BPD measurement used together with a higher cut-off level than usual. For example, using a cut-off level of 3.0 MoM the detection rate for open spina bifida at 16-18 weeks gestation would be about 88% and the proportion of unaffected singleton pregnancies with raised levels only 0.9%. These results are materially better than those achieved by a policy of scanning only those women with a raised AFP level (79% and 1.4% respectively with a more conventional cut-off level of 2.5 MoM) or, in addition, scanning those with doubtful gestational ages (82% and 1.7% respectively with a cut-off level of 2.5 MoM).

The effect of maternal weight on maternal serum alpha-fetoprotein levels

In 902 singleton pregnancies, maternal serum alpha-fetoprotein (AFP) levels between 15 and 20 weeks of pregnancy were significantly related to maternal weight (r = 0.24, p less than 0.0001). Lighter women had on average higher AFP levels than heavier women, perhaps on account of the greater concentration of AFP in their relatively smaller volume of blood. The mean AFP level for women weighing less than 45 kg was 68% higher than the mean level for women weighing 85 kg or more. Maternal weight was found to be an important factor which could account for false positive AFP results in antenatal screening for open neural tube defects. A policy of adjusting maternal serum AFP values according to maternal weight among women with borderline positive results could reduce the number having a diagnostic amniocentesis with only a negligible loss of detection for open spina bifida. With such a policy, using a cut-off level of 2.5 x normal median, the false positive rate in the 902 women screened would have been reduced fom 2.8% to 2.0%.

A note on the role of dietary retinol and carotene in human gastro-intestinal cancer

Dietary data relating in 406 patients with gastrointestinal cancers (cases) and 812 controls have been analysed to test the hypotheses that dietary vitamin A (retinol) and its precursor, carotene, may be protective agents in human carcinogenesis. There was no deficit among cases in the intake of retinol-containing food items whereas several of the main carotene-containing fruits and vegetables were eaten less often among cases than among controls. However, when total daily intake was estimated, there was no protective effect of carotene, perhaps implying that some other constituent of the fruits and vegetables is protective.

Small biparietal diameter of fetuses with spina bifida: implications for antenatal screening

The biparietal diameter of 20 fetuses with spina bifida was measured during pregnancy by ultrasound scanning, mainly in the second trimester. The mean result was 0.83 cm smaller than the value based on 186 unaffected pregnancies at the same gestational ages (P less than 0.001), suggesting that spina bifida fetuses are growth retarded. The practical consequence of this finding is that the routine use of ultrasound in pregnancy will increase the sensitivity of AFP screening for open spina bifida at 16 to 18 weeks gestation from 79 per cent as estimated by the UK Collaborative AFP Study to about 90 per cent or more.

Maternal serum alpha-fetoprotein and diabetes mellitus

Maternal serum alpha-fetoprotein (AFP) levels were measured from 12 to 24 weeks gestation in 27 singleton pregnancies in women with insulin-dependent diabetes mellitus and 90 controls without diabetes who were matched for gestational age. The geometric mean AFP level among the diabetic pregnancies was 60 per cent of that in the controls, a difference which was statistically significant (P less than 0.01). The difference in AFP level between diabetic patients and controls was most marked in sera taken before 21 weeks gestation.

Maternal serum alpha-fetoprotein and birth weight in twin pregnancies

In 102 twin pregnancies the mean birth weight of each pair showed a statistically significant negative association with maternal serum alpha-fetoprotein (AFP) levels early in pregnancy. Women with AFP levels of four or more times the median value for singleton pregnancies gave birth to infants with a median birth weight 660 g less than that of infants born to women with AFP levels between 1.0 and 1.5 times the median for singleton pregnancies. Maternal serum AFP has been shown to be an early predictor of low birth weight delivery in singleton pregnancies. Our results indicate that this is also true in twin pregnancies.

Maternal serum alpha-fetoprotein levels in triplet and quadruplet pregnancy

Maternal serum alpha-fetoprotein (AFP) levels were higher in six triplet pregnancies and three quadruplet pregnancies than in control singleton pregnancies matched for maternal age, parity and time of gestation at which the serum sample was taken. Between 12 and 23 weeks of pregnancy, the average AFP levels among the triplet pregnancies was three times that found in the singleton pregnancies, and the level in the quadruplet pregnancies was even higher. Maternal serum AFP levels appear to be associated with the number of fetuses in utero.

Maternal serum-alpha-fetoprotein and low birth-weight

High maternal serum-alpha-fetoprotein (A.F.P.) concentrations in the first half of pregnancy were associated with prematurity and high perinatal mortality. 94 singleton pregnancies without neural-tube defects but with A.F.P. levels equal to or greater than three times the normal median resulted in the birth of infants weighing, on average, 357 g less than controls (P less than 0-001). The mean head circumference of the infants was also smaller than that of the controls. The 1 stillbirth and 3 neonatal deaths yielded a mortality-rate more than three and a half times that for singleton births without neural-tube defects at the same hospital in the years 1974-76. The results suggest that some pregnant women who will deliver low-birth-weight infants at high risk of perinatal death may be identified by means of serum-A.F.P. measurement early in pregnancy.

Maternal serum-alpha-fetoprotein measurement in antenatal screening for anencephaly and spina bifida in early pregnancy. Report of U.K. collaborative study on alpha-fetoprotein in relation to neural-tube defects

Nineteen centres collaborated in a study to determine the efficiency of maternal serum-alpha-fetoprotein (A.F.P.) measurement as a method of screening for neural-tube defects (N.T.D.S.) between 10 and 24 weeks of pregnancy. Data were collected on 18 684 singleton pregnancies and 163 twin pregnancies without fetal N.T.D.s, and on 301 singleton pregnancies with fetal N.T.D.s (146 with anencephaly, 142 with spina bifida, and 13 with encephalocele). The best time for detecting open spina bifida by measuring maternal serum-A.F.P. is at 16-18 weeks of pregnancy. In clinical practice, serum-A.F.P. cut-off levels expressed as multiples of the normal median may be more convenient to use than percentiles because they are easier to derive and more stable. Also, the proportion of affected pregnancies with serum-A.F.P. levels exceeding a given multiple of the median is unlikely to vary significantly from centre to centre or over time. In contrast, the proportion of unaffected pregnancies with A.F.P. levels exceeding a given multiple of the normal median will vary depending on the precision with which serum-A.F.P. and gestation are measured. At 16-18 weeks of pregnancy 88% of cases of anencephaly, 79% of cases of open spina bifida, and 3% of unaffected singleton pregnancies had A.F.P. levels equal to or greater than 2-5 times the median for unaffected singleton pregnancies. At this gestation age the numbers of unaffected pregnancies with A.F.P. levels above 2-5 times the normal median can be reduced by about a third if women with borderline A.F.P. levels are retested, although this would not greatly change the detection-rate of affected pregnancies. In the United Kingdom as a whole, women with serum-A.F.P. levels above 2-5 times the normal median at 16-18 weeks of gestation will have an approximately 1-in-20 chance of having a fetus with open spina bifida; the risk of having any N.T.D. will be approximately 1 in 10. The results of this study indicate that screening pregnant women by measuring the concentration of A.F.P. in their serum is an effective method of selecting women for ultrasonography and amniocentesis so that N.T.D.s can be diagnosed in utero.

Maternal serum alpha-fetoprotein and spontaneous abortion

The relationship between spontaneous abortion and maternal serum alpha-fetoprotein (AFP) levels was investigated between 9 and 25 weeks of pregnancy. Seven out of 126 (5-6 per cent) women who had spontaneous abortions had raised maternal serum AFP levels at their antenatal booking visit compared to 4 out of 247 (1-6 per cent) control patients who were delivered of single liveborn infants, a statistically significant differences. The raised AFP concentrations were, however, associated with spontaneous abortion only if the serum samples had been taken immediately before, or at sometime after the abortion was first clinically suspected. This suggests that high levels do not predict the development of abortion in women who have not already threatened to abort. It is therefore unlikely that women who have not already threatened to abort. Therefore, when maternal serum AFP levels are used to screen for fetal neural tube defects, women referred for a diagnostic amniocentesis on account of a high level are unlikely to have been selected on the basis of a tendency to abort.