Clinical validation of a new dimeric inhibin-A assay suitable for second trimester Down's syndrome screening

Objective To compare the Down's syndrome screening performance of a simplified dimeric inhibin-A assay (Diagnostic Systems Laboratories (DSL)) with an assay whose clinical utility has been established (Serotec).

Setting A case control set consisting of 51 Down's syndrome and 245 matched unaffected pregnancies collected as part of an earlier multicentre cohort study.

Methods Sera were assayed for dimeric inhibin-A using the DSL assay and Serotec reference assay. Data analysis included a method comparison of mass values, fit of data to a logarithmic Gaussian distribution, and determination of detection and false positive rates. In addition, 234 fresh sera were assayed using the simplified method.

Results The two assays showed a high correlation (r =0.93) but average concentrations of the DSL assay were 48% higher. However, the differences were basically proportional over the range of values important for screening. The detection rate was essentially equivalent for the DSL assay whether analysed univariately or in combination with other markers (for example, 79% v 75% at a 5% false positive rate for the DSL and Serotec assays for the combination of α fetoprotein, unconjugated oestriol, human chorionic gonadotrophin, and dimeric inhibin-A, respectively). The 234 dimeric inhibin-A values measured on fresh sera fitted a logarithm Gaussian distribution for the DSL assay, as indicated by the fit to a probability plot.

Conclusions The Down's syndrome screening performance of a simplified dimeric inhibin-A immunoassay was equivalent to a more labour intensive established dimeric inhibin-A assay.

The reference range and within-person variability of thyroid stimulating hormone during the first and second trimesters of pregnancy

OBJECTIVE

To further explore first and second trimester reference ranges for thyroid stimulating hormone (TSH) and examine within-person variability of TSH and thyroid peroxidase (TPO) antibody.

SETTING

Women coming for routine prenatal care in early pregnancy agreed to participate in a trial of integrated serum screening for Down's syndrome. Two serum samples were obtained from each woman, one each in the first and second trimesters. These samples were also available for TSH and TPO measurements in the present study.

METHODS

TSH and TPO antibody measurements were performed in 1126 women with ultrasound-dated pregnancies who provided serum samples in both trimesters. TSH reference ranges were established for the entire cohort and for the antibody-negative subgroup. Within-person variability of TSH measurements between trimesters was examined.

RESULTS

Median TSH values are lower in the first trimester than in the second (1.00 versus 1.29 mIU/l), but 98th centile values are higher (5.20 versus 4.18 mIU/l). High correlation exists between individual women's first and second trimester TSH measurements (r=0.75, r2=0.56, p<0.001). Among 23 women with TSH values above the 98th centile in the second trimester, 17 (74%) were over the 95th centile in the first trimester. TPO antibody measurements are also highly correlated between trimesters (r=0.97, r)=0.94).

CONCLUSION

Proper interpretation of TSH measurements during pregnancy requires that laboratories establish and monitor appropriate reference ranges. TSH levels show high within-person consistency between trimesters.

Assigning risk for Smith-Lemli-Opitz syndrome as part of 2nd trimester screening for Down's syndrome

OBJECTIVES

To design a reliable model in the context of prenatal screening for assigning the risk in an individual pregnancy of Smith-Lemli-Opitz syndrome (SLOS) and assess its performance.

SETTING

A 2nd trimester screening programme for Down's syndrome that measures unconjugated estriol (uE3) along with other serum markers.

METHODS

Development of individual risk estimates with a trivariate model incorporating measurements of maternal serum uE3, alpha-fetoprotein (AFP), and human chorionic gonadotropin (hCG) in both SLOS and unaffected pregnancies.

RESULTS

Population parameters were computed for the three analytes, as were pairwise correlation coefficients and truncation limits, based on an unbiased collection of 29 affected pregnancies. Published parameters were used for unaffected pregnancies. With a cut off level of risk of 1:50, 62% of SLOS pregnancies can be detected by initially identifying 0.34% of unaffected pregnancies as screen positive. About 1 in 90 screen positive pregnancies will be affected.

CONCLUSIONS

It is possible to screen for SLOS as an add on to existing 2nd trimester maternal serum screening, if uE3 is already being measured. A large, prospective trial is necessary to determine whether diagnostic testing can be performed in maternal urine or serum rather than amniotic fluid.

Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child

BACKGROUND

When thyroid deficiency occurs simultaneously in a pregnant woman and her fetus, the child's neuropsychological development is adversely affected. Whether developmental problems occur when only the mother has hypothyroidism during pregnancy is not known.

METHODS

In 1996 and 1997, we measured thyrotropin in stored serum samples collected from 25,216 pregnant women between January 1987 and March 1990. We then located 47 women with serum thyrotropin concentrations at or above the 99.7th percentile of the values for all the pregnant women, 15 women with values between the 98th and 99.6th percentiles, inclusive, in combination with low thyroxine levels, and 124 matched women with normal values. Their seven-to-nine-year-old children, none of whom had hypothyroidism as newborns, underwent 15 tests relating to intelligence, attention, language, reading ability, school performance, and visual-motor performance.

RESULTS

The children of the 62 women with high serum thyrotropin concentrations performed slightly less well on all 15 tests. Their full-scale IQ scores on the Wechsler Intelligence Scale for Children, third edition, averaged 4 points lower than those of the children of the 124 matched control women (P= 0.06); 15 percent had scores of 85 or less, as compared with 5 percent of the matched control children. Of the 62 women with thyroid deficiency, 48 were not treated for the condition during the pregnancy under study. The full-scale IQ scores of their children averaged 7 points lower than those of the 124 matched control children (P=0.005); 19 percent had scores of 85 or less. Eleven years after the pregnancy under study, 64 percent of the untreated women and 4 percent of the matched control women had confirmed hypothyroidism.

CONCLUSIONS

Undiagnosed hypothyroidism in pregnant women may adversely affect their fetuses; therefore, screening for thyroid deficiency during pregnancy may be warranted.

Antepartum fetal and maternal carboxyhemoglobin and cotinine levels among cigarette smokers

The objective of this study was to examine the association of carboxyhemoglobin (COHb) and plasma cotinine levels among pregnant women who smoke cigarettes and their fetuses. Fifteen pregnant women who smoked and their fetuses undergoing cordocentesis had blood samples analysed simultaneously for COHb and cotinine. Linear regression was used to test for associations among study variables. Significant maternal-fetal associations were observed both with COHb (r = 0.72, p = 0.003) and with cotinine (r = 0.96, p = 0.003). Maternal cotinine levels were correlated with maternal and fetal COHb levels (r = 0.96, p = 0.003; r = 0.99, p = 0.0003, respectively). Fetal cotinine levels were correlated with COHb in maternal and in fetal blood (r = 0.81, p = 0.0003; r = 0.88, p<0.0001, respectively). The strong direct associations of maternal and fetal levels of COHb and cotinine indicate that maternal COHb and cotinine measurements may be interpreted as surrogates of fetal COHb levels. However, the specificity, ex vivo stability and ease of measurement of cotinine offer advantages over using COHb in quantifying fetal CO exposure following maternal cigarette smoking.

Invasive meningococcal infection in Western Australia

OBJECTIVES

To review signs and symptoms in children diagnosed with meningococcal infection; to assess age, sex and race distribution of meningococcal infection; and to assess associations of the presenting features with morbidity and mortality.

DESIGN

Retrospective case notes review for a 5-year period.

SUBJECTS

105 patients aged between 19 days and 13 years. MAIN DATA REVIEWED: Temperature, blood pressure, heart rate, respiratory rate, type of rash, age, sex, race and outcome.

RESULTS

Of the 105 patients, 67.6% were Caucasian, 27.6% Aboriginal and 4.8% of other origin. There were 14.3% patients under 3 months of age (2.9% neonates), 48.6% between 3 months and 2 years, 21% between 2 and 4 years and 16.2% older than 4 years. The male:female ratio was 1.4. Features at presentation in decreasing order of frequency were: fever (89.5%), tachypnoea (73.3%), rash (59% [maculopapular 17.1%, petechial 27.6% and purpuric 14.3%]), vomiting (52.4%), irritability (44.8%), tachycardia (37.5%), lethargy (36.2%), neck stiffness (32.4%) and non-specific immediately preceding illness (15.2%). Purpura and a reduced systolic blood pressure were significantly associated with an increased risk of mortality, purpura and reduced diastolic blood pressure with an increased risk of morbidity. Initial misdiagnosis occurred in 17.1% of cases, with the majority of those misdiagnosed (83.3%) aged less than 2 years. Predominant serotyping was Group B followed by Group C. Major findings were a marked male preponderance in patients under 3 months of age. The incidence of meningococcal infection in the Aboriginal population was approximately six times that in the non-Aboriginal population. The yearly incidence of meningococcal disease during the study period ranged from 5.2 to 10.5 per 100,000. Long-term morbidity occurred in 8.6% of cases and mortality was 8.6%. Higher morbidity and mortality figures were found in those with septicaemia alone. Children referred from peripheral hospitals had a higher mortality but a comparable morbidity.

Second trimester screening for Down's syndrome using maternal serum dimeric inhibin A

OBJECTIVES

To determine the second trimester Down's syndrome screening performance of maternal serum dimeric inhibin A, both alone and in combination with existing serum markers.

SETTING

A case-control set of serum samples from patients with Down's syndrome (52) and subjects with matched unaffected pregnancies obtained in a previous cohort study before second trimester amniocentesis and karyotyping. The amniocenteses were performed for reasons other than a positive serum screening test result.

METHODS

For each serum from a Down's syndrome pregnancy, five serum samples from pregnancies with a normal karyotype were matched for recruitment centre, gestational age, maternal age, and date of amniocentesis. A specific form of inhibin (dimeric inhibin A) was measured using monoclonal antibodies. Measurements of alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin and its free beta subunit were already available. Screening performance was modelled using distribution variables of the analytes coupled with the 1993 age distribution of pregnant women in the United States.

RESULTS

The median dimeric inhibin A level was 2.10 times higher in Down's syndrome pregnancies. When dimeric inhibin A was combined with maternal age and three other serum markers (alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin) the Down's syndrome detection rate increased to 75% (from 66%) at a 5% false positive rate. If dimeric inhibin A could be added for less than $31 (ranging from $16 to $39 depending on the detection rate, markers chosen, and method of dating), the cost of detecting each Down's syndrome pregnancy and the number of procedure related fetal losses would both be reduced.

CONCLUSIONS

The addition of dimeric inhibin A to prenatal screening programmes for Down's syndrome should be considered, or possibly it could be substituted for an existing serum marker. One barrier to implementation in the United States, however, is the unavailability of kits with Food and Drug Administration approval.

Screening of maternal serum for fetal Down's syndrome in the first trimester

BACKGROUND

Screening of maternal serum to identify fetuses with Down's syndrome is now routinely offered during the second trimester of pregnancy. Prenatal screening by means of serum assays or ultrasonographic measurements, either alone or in combination, may also be possible in the first trimester.

METHODS

We measured serum alpha-fetoprotein, unconjugated estriol, human chorionic gonadotropin (hCG), the free beta subunit of hCG, and pregnancy-associated protein A in 4412 women (82 percent of whom were 35 years of age or older) who came to 16 prenatal diagnostic centers for chorionic-villus sampling or early amniocentesis at 9 to 15 weeks of gestation. Ultrasound measurements of fetal nuchal translucency were also reported. Fetal chromosomal analysis was performed in all pregnancies. Altogether, there were 61 fetuses with Down's syndrome.

RESULTS

A total of 48 pregnancies affected by Down's syndrome and 3169 unaffected pregnancies were identified before 14 weeks of gestation; the rates of detection of Down's syndrome for the five serum markers were as follows: 17 percent for alpha-fetoprotein, 4 percent for unconjugated estriol, 29 percent for hCG, 25 percent for the free beta subunit of hCG, and 42 percent for pregnancy-associated protein A, at false positive rates of 5 percent. The results of the measurements of serum hCG and its free beta subunit were highly correlated. When used in combination with the serum concentration of pregnancy-associated protein A and maternal age, the detection rate was 63 percent for hCG (95 percent confidence interval, 47 to 76 percent) and 60 percent for its free beta subunit (95 percent confidence interval, 45 to 74 percent). Measurements of nuchal translucency varied considerably between centers and could not be reliably incorporated into our calculations.

CONCLUSIONS

Screening for Down's syndrome in the first trimester is feasible, with use of measurements of pregnancy-associated protein A and either hCG or its free beta subunit in maternal serum.

hCG and the free beta-subunit as screening tests for Down syndrome

Published studies have reached varying conclusions as to the benefit of replacing human chorionic gonadotropin (hCG) measurements with the free beta-subunit of hCG (the free beta-subunit) for Down syndrome screening. One study reports 14 per cent higher detection for the free beta-subunit, while another finds an actual loss in detection. To explore this issue further, we directly compared the screening performance of hCG and the free beta-subunit, alone and in combination with other serum markers, using banked sera obtained prior to amniocentesis and karyotyping. Altogether, 52 Down syndrome and 5065 unaffected pregnancies were studied. Sera were thawed and assayed for hCG and the free beta-subunit over 1 year. At a 5 per cent false-positive rate, the detection rate for hCG in combination with maternal age and alpha-fetoprotein was higher than when the free beta-subunit was substituted (62 versus 57 per cent). Ultrasound dating and adding unconjugated oestriol both increased detection. The present findings, along with those from six case control studies (our re-analysis), indicate that the screening performances of hCG and the free beta-subunit are similar (median change in detection 0, range -8 to +3 per cent). Under optimal sample collection and transportation conditions, laboratories can expect to achieve similar screening performance using either hCG or the free beta-subunit measurements.

Screening for Down syndrome at 14 weeks of pregnancy

To investigate whether statistical parameters used in Down syndrome screening between 15 and 22 weeks of pregnancy can be used at 14 weeks, we assayed alpha-fetoprotein (AFP), unconjugated oestriol (uE3), total human chorionic gonadotrophin (hCG), free alpha-hCG, free beta-hCG, and inhibin-A in 16 pregnancies with Down syndrome in the 14th week of pregnancy and expressed values in multiples of the normal median. The median and standard deviation values for these 16 pregnancies were not materially different from those published for 15-22 weeks. It is reasonable, therefore, to offer Down syndrome screening using these markers starting at 14 completed weeks of pregnancy instead of 15 weeks. It needs to be recognized, however, that serum AFP measurement for neural tube defect screening is less effective at this time than between 16 and 18 weeks of pregnancy.

Maternal serum screening for Down syndrome in the United States: a 1995 survey

OBJECTIVE

Our goal was to determine the status of prenatal Down syndrome screening in the United States in 1995.

STUDY DESIGN

Information was sought via questionnaire from laboratories participating in external proficiency testing.

RESULTS

Services were provided to 2,498,000 women annually by 265 screening laboratories. All but 10 laboratories offered both open neural tube defect and Down syndrome screening. Twenty-one percent of Down syndrome interpretations were based on alpha-fetoprotein measurements alone; 79% also included other serum analytes. Sixty-six laboratories (26%) offered interpretations at 14 weeks' gestation or earlier.

CONCLUSIONS

Some laboratories extend serum screening too early in gestation for optimal neural tube defect interpretation. When 1995 was compared with 1992, more women were being screened, a higher proportion were receiving a Down syndrome interpretation, and more interpretations were based on multiple analytes. Laboratories should be encouraged to use some combination of multiple markers when screening for Down syndrome.

Quality assessment of a prenatal screening program

Epidemiologic monitoring is a process which uses data generated from the screened population as a quality control measure. Most commonly, laboratories monitor the percentage of women with screen positive test results, i.e., with test results falling at or above a specified multiple of the median (MoM) for open neural tube defect screening or, with a risk at or above a specified risk cut-off for Down's syndrome screening. These percentages are sensitive to inaccurate and imprecise assays, inappropriate reference data, and long term assay drift. In fetal Down's syndrome screening it is necessary to simultaneously monitor two or more assays, which is accomplished by monitoring the median MoM for each assay (which should be 1.0 within statistical limits) calculated using patient MoM values. Monitoring the median MoM can identify inappropriate adjustment factors for variables which affect the MoM such as maternal weight. Epidemiologic monitoring is a useful tool for identifying problems which are not readily apparent using traditional quality control measures.

Refinements in managing maternal weight adjustment for interpreting prenatal screening results

This study examines the relationship between maternal weight and serum levels of alpha-fetoprotein, unconjugated oestriol, and human chorionic gonadotropin in a population of 47,585 women being provided with prenatal screening for Down's syndrome and open neural tube defects. The study population contains sufficient numbers of women at the extremes of weight to allow the determination that a reciprocal-linear equation more accurately describes the weight relationship for two of the three analytes than the currently used log-linear equations. The reciprocal-linear equations, while more appropriate, provide only a minimal advantage over the log-linear equations. A more important finding is that published weight equations may not be optimal for some screening programmes, due to differences in the mean weight of the populations being tested. Screening programmes are encouraged to calculate their own weight correction formulae, based on data from their own population, and to monitor the mean maternal weight to detect when modifications in the weight correction formulae might be indicated.

Multiple marker screening for Down syndrome in twin pregnancies

This study documents the screening performance, in practice, of a published protocol for interpreting second-trimester Down syndrome risk in twin pregnancies, using maternal serum biochemical markers. Within a cohort of 35,150 pregnancies, 410 twin pregnancies were identified. The rate of twinning was positively associated with maternal age. Of the 274 twin pregnancies known prior to screening, 15 (5.5 per cent) were classified as being screen-positive for Down syndrome. When maternal age and dating method were taken into account, the screen-positive rates in twin and singleton pregnancies did not differ significantly. Nine of the 14 screen-positive women with viable twin pregnancies chose amniocentesis [64 per cent, 95 per cent confidence interval (CI) 35-87]. No cases of Down syndrome were identified. Based on modelling, an estimated 73 per cent of monozygotic twin pregnancies and 43 per cent of dizygotic twin pregnancies with Down syndrome would be identified at a 5 per cent false-positive rate. The overall detection rate would be about 53 per cent. When laboratories offer multiple marker screening to women with twin pregnancies, the false-positive rate ought to be similar to that found in singleton pregnancies; the detection rate is, however, likely to be lower for dizygotic twins.

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

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

Elevated midtrimester serum methylmalonic acid levels as a risk factor for neural tube defects

The role of folic acid in the primary prevention of neural tube defects (NTDs) is well established. However, questions related to the protective mechanism remain unanswered. To help answer these questions, we designed a case-control study to assess the role of folate- and cobalamin-related metabolites in the pathogenesis of NTDs. Concentrations of folate, cobalamin, and 14 other related metabolites were measured by gas chromatography/mass spectrometry in midtrimester serum specimens from 32 women with an NTD-affected pregnancy and from 132 control women, and in serum specimens from 46 nonpregnant women who had a history of NTD-affected pregnancy and from 43 nonpregnant control women. Log-transformed means of metabolites were compared between case and control women for both the midtrimester and nonpregnant groups. In the pregnant group, serum methylmalonic acid (MMA) concentrations were higher among case women than among control women (130 vs 105 nM). There was a strong dose-response relationship between midtrimester serum MMA level and the risk for an NTD-affected pregnancy, with the relative risk increasing 13-fold for women with MMA levels > 90th percentile. In the nonpregnant group, there was no difference in serum MMA levels between case and control women (140 vs 140 nM). Thus, the serum MMA levels of women in the midtrimester of pregnancies unaffected by NTDs were significantly lower than the levels of nonpregnant women, whereas the levels of women whose pregnancies were affected by NTDs were similar to those of nonpregnant women. The finding of elevated MMA serum concentrations among women in the midtrimester of NTD-affected pregnancies suggests that cobalamin may be involved in the etiology of NTDs. The possible role of cobalamin in relation to the protective effect of folic acid needs further evaluation.

Effect of parity on human chorionic gonadotrophin levels and Down's syndrome screening

OBJECTIVE

To investigate further the association between parity and human chorionic gonadotrophin (hCG) levels during the second trimester and determine whether prenatal screening for Down's syndrome might be made more efficient by adjusting for this variable.

METHODS

Measurements of hCG were analysed in relation to parity from a cohort of 16,675 singleton pregnancies with viable outcomes, and from 108 singleton pregnancies affected by Down's syndrome. Cigarette smoking during pregnancy and maternal age were also analysed in relation to hCG levels.

RESULTS

For both unaffected pregnancies and pregnancies with Down's syndrome the median hCG levels were 7% lower in parous than in nulliparous women. A dose-response relation was also documented for the unaffected pregnancies. When para 0, para 1, and para 2 women were studied separately, hCG levels rose steadily as age advanced. Adjusting hCG levels for parity led to a 0.1% reduction in variance of the distribution of hCG measurements in unaffected pregnancies and to a negligible increase in Down's syndrome screening efficiency.

CONCLUSION

The effect of parity is not sufficiently great to warrant routine adjustment of hCG levels as part of prenatal screening for Down's syndrome.

Second-trimester maternal serum alpha-fetoprotein, unconjugated estriol, and hCG levels in pregnancies with ventral wall defects

OBJECTIVE

To determine if second-trimester maternal serum concentrations of unconjugated estriol (E3) and hCG are altered in pregnancies associated with fetal gastroschisis or omphalocele.

METHODS

Concentrations of alpha-fetoprotein (AFP), unconjugated E3, and hCG were measured in a case-control study involving 23 cases of gastroschisis, 17 cases of omphalocele, and 200 matched unaffected pregnancies.

RESULTS

As reported previously, median AFP levels were significantly higher in pregnancies with gastroschisis and omphalocele compared to unaffected pregnancies (9.42 and 4.18 multiples of the unaffected population median [MoM], respectively). The median hCG values were not significantly different for the two defects (1.10 and 1.13 MoM, respectively). Six of the cases of omphalocele were associated with other anomalies, but exclusion of these cases from the analysis did not alter the conclusions.

CONCLUSIONS

Unconjugated E3 and hCG measurements are not useful in screening for, or distinguishing between, open ventral wall defects. Alpha-fetoprotein measurements alone will detect nearly all cases of gastroschisis and most cases of omphalocele.

Second-trimester diurnal variation of maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated oestriol: is it present and does it affect the prediction of a patient's risk for fetal Down syndrome?

Both a cross-sectional and a longitudinal study were performed to investigate whether or not the collection time should be taken into consideration when generating a patient's risk for fetal Down syndrome with multiple marker screening. Diurnal variations of third-trimester alpha-fetoprotein (AFP) levels and first-trimester human chorionic gonadotropin (hCG) levels have been previously reported. In addition, large episodic fluctuations of conjugated and unconjugated oestriol (uE3) as well as a diurnal variation have also been reported in the third trimester. If the levels of these analytes routinely fluctuate during the day, they could affect a patient's risk calculation for fetal Down syndrome. The longitudinal study evaluated ten non-diabetic women who underwent sequential sampling for AFP, hCG, and uE3. The cross-sectional study evaluated 1953 patients for these three markers whose time of sampling was recorded between 8.00 a.m. and 5.59 p.m. Using either study design, no significant effect was seen in the median MOM levels of the screening analytes as a function of the time of day.

Reducing the need for amniocentesis in women 35 years of age or older with serum markers for screening

BACKGROUND

As maternal age advances, the risk of fetal Down's syndrome increases. Pregnant women 35 years of age or older are routinely offered amniocentesis because of this risk. Recently, maternal serum markers have been reported to be useful in screening for Down's syndrome, primarily in younger women. We therefore investigated whether offering amniocentesis only to selected women 35 years of age or older who were identified by screening measurements in serum might prove a useful alternative to the current practice.

METHODS

We studied 5385 women with singleton pregnancies who were 35 years of age or older and were undergoing routine amniocentesis. Along with information about the pregnancy, we obtained a serum sample for measurement of alpha-fetoprotein, unconjugated estriol, and human chorionic gonadotropin. Individual estimates of the risk of Down's syndrome in the fetus were calculated for each pregnancy before the karyotype was known.

RESULTS

If amniocentesis had been reserved for the women calculated to have a risk greater than 1 in 200 of having a fetus with Down's syndrome, 48 of the 54 cases of Down's syndrome (89 percent) would have been identified, 25 percent of the unaffected pregnancies would also have been identified as being at high risk for Down's syndrome (false positives). Seven of 15 fetuses (47 percent) with other trisomies, 11 of 25 (44 percent) with sex aneuploidy, and 1 of 9 (11 percent) with miscellaneous chromosomal abnormalities would also have been detected. In practice, such screening would have made 75 percent of the amniocentesis unnecessary, along with a proportion of the amniocentesis-associated fetal losses. If the cutoff for the risk of Down's syndrome were set higher than 1 in 200, both the rate of detection and the false positive rate would be lower. Conversely, these rates would be higher if the cutoff were set lower.

CONCLUSIONS

Prenatal screening of serum to generate individual estimates of the risk of Down's syndrome in the fetus can provide a basis for decision making in the cases of women 35 years of age or older, as it does in younger pregnant women, and is an alternative to current testing practices.

Replacing creatinine measurements with specific gravity values to adjust urine cotinine concentrations

Creatinine and specific gravity (relative density) measurements both allow differences in urine concentration to be taken into account in determining urine cotinine concentrations. In this study we demonstrate that the variance of urine cotinine measurements is reduced comparably when either creatinine or specific gravity measurements are used for correction. This reduction in variability improves the correlation between urine cotinine measurements and clinical endpoints. In this study, the clinical endpoints were pulmonary function in a population of nonsmoking children with asthma, 42% of whom were reported to have been exposed to environmental tobacco smoke. When corrected by either creatinine measurements or specific gravity values, the urine cotinine measurements performed as well or better than reported exposure (and comparably with each other) in assessments of lung function. A dose-response relationship was also more consistently apparent. Specific gravity values can be used reliably in place of creatinine values to adjust urine cotinine measurements for both research and clinical purposes.

Replacing creatinine measurements with specific gravity values to adjust urine cotinine concentrations

Creatinine and specific gravity (relative density) measurements both allow differences in urine concentration to be taken into account in determining urine cotinine concentrations. In this study we demonstrate that the variance of urine cotinine measurements is reduced comparably when either creatinine or specific gravity measurements are used for correction. This reduction in variability improves the correlation between urine cotinine measurements and clinical endpoints. In this study, the clinical endpoints were pulmonary function in a population of nonsmoking children with asthma, 42% of whom were reported to have been exposed to environmental tobacco smoke. When corrected by either creatinine measurements or specific gravity values, the urine cotinine measurements performed as well or better than reported exposure (and comparably with each other) in assessments of lung function. A dose-response relationship was also more consistently apparent. Specific gravity values can be used reliably in place of creatinine values to adjust urine cotinine measurements for both research and clinical purposes.

Human chorionic gonadotropin and unconjugated oestriol measurements in insulin-dependent diabetic pregnant women being screened for fetal Down syndrome

This prospective study investigates the relationship between insulin-dependent diabetes and maternal serum levels of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG). It also examines the potential impact on screening for Down syndrome. The population-based cohort included 20,321 pregnant women in Maine who underwent routine serum screening for Down syndrome in the second trimester. The cohort included 52 women with insulin-dependent diabetes. Maternal serum AFP levels are now routinely adjusted for insulin-dependent diabetes. These adjustments, therefore, were made routinely in the diabetic women, but no equivalent adjustments were made for uE3 and hCG values. The initial false-positive rate (using all three markers) among the women with diabetes was not significantly different from that in the non-diabetic population (7.7 and 5.4 per cent, respectively). Prior to adjustment for insulin-dependent diabetes, the median AFP level in the 52 women was 0.73 multiples of the median (MOM); the median levels of uE3 and hCG were 0.93 and 0.98 MOM, respectively. When the uE3 and hCG levels were adjusted, the initial false-positive rate was unchanged. Median serum levels of uE3 were significantly higher in the 33 women whose onset of diabetes was prior to 19 years of age (0.99 MOM) than in the 19 women whose onset of diabetes was at age 19 or older (0.84 MOM). This is the first population-based study to investigate the relationship between diabetes and serum levels of AFP, uE3, and hCG, and confirms earlier observations from a case-control study that found only slightly lower uE3 and hCG levels.

Maternal serum screening for fetal Down syndrome in the United States: a 1992 survey

OBJECTIVE

Our purpose was to determine the status of screening for fetal Down syndrome in the United States in 1992.

STUDY DESIGN

Information was sought from laboratories participating in two proficiency testing programs.

RESULTS

The 301 responding laboratories (98%) annually provided services to 2,113,000 pregnant women. Of these laboratories, 242 provided Down syndrome screening (1,924,000 pregnant women); 55% used alpha-fetoprotein levels alone, 30% used alpha-fetoprotein, unconjugated estriol, and human chorionic gonadotropin combined, and 14% used alpha-fetoprotein and human chorionic gonadotropin combined. All laboratories used clinically validated analytes. Nearly all screened at appropriate gestational ages, used a validated algorithm, and used risk as the screening variable. However, many laboratories, especially smaller ones, were unable to monitor their performances adequately.

CONCLUSION

Since 1988 maternal serum screening for Down syndrome has approximately doubled, and other analyte measurements have been added in nearly one fourth of the screened pregnancies. Most laboratories appear to be performing adequately, although there is room for improvement.

Association between exposure to environmental tobacco smoke and exacerbations of asthma in children

BACKGROUND

Exposure to environmental tobacco smoke, as reported by parents, has been linked to diminished pulmonary function and more frequent exacerbations of asthma in children with the disease. Further insight into this association might be gained by using urine cotinine levels to measure actual exposure.

METHODS

We measured urine cotinine levels in 199 children with asthma; 145 also underwent pulmonary-function studies. A parent answered questions about each child's exposure to environmental tobacco smoke. Acute exacerbations of asthma during the preceding year were documented through blinded review of medical records. Possible confounding factors were accounted for by the use of multivariate analysis and by comparisons of serum theophylline levels in exposed and unexposed children.

RESULTS

The median urine cotinine levels were 5.6 ng per milliliter in the 116 children reported not to have been exposed to tobacco smoke, 13.1 ng per milliliter in the 53 children exposed to cigarette smoking by the mother or other persons, and 55.8 ng per milliliter in the 30 children exposed to cigarette smoking by the mother and other persons. Acute exacerbations of asthma increased with exposure, whether such exposure was reported by a parent or identified on the basis of the cotinine level; the relative risks for the highest as compared with the lowest exposure category were 1.8 (95 percent confidence interval, 1.4 to 2.2) for reported exposure and 1.7 (95 percent confidence interval, 1.4 to 2.1) for exposure indicated by cotinine levels. The forced expiratory volume in one second (FEV1), the forced expiratory flow between 25 and 75 percent of vital capacity, and the ratio of FEV1 to forced vital capacity also decreased with increases in both measures of exposure.

CONCLUSIONS

Measurement of urine cotinine levels provides further evidence of an association between exposure to environmental tobacco smoke and pulmonary morbidity in children with asthma. These data emphasize the need for systematic, persistent efforts to stop the exposure of children with asthma to environmental tobacco smoke.

Cigarette smoking and levels of maternal serum alpha-fetoprotein, unconjugated estriol, and hCG: impact on Down syndrome screening

OBJECTIVE

To investigate the association between maternal cigarette smoking and serum levels of alpha-fetoprotein (AFP), unconjugated estriol (uE3), and hCG and to determine whether it is appropriate to take smoking status into account when screening for fetal Down syndrome.

METHODS

Smoking information was obtained from 23,668 pregnant women at the time of routine screening for fetal Down syndrome. Serum levels of AFP, uE3, and hCG were stratified by smoking status and compared. Individual risks for fetal Down syndrome were analyzed both before and after adjusting the hCG levels for the effect of smoking. The prevalence of Down syndrome in the study population was calculated for both smokers and non-smokers.

RESULTS

The average AFP, uE3, and hCG levels in women who smoked cigarettes were 3% greater (95% confidence interval [CI] 2-4%), 3% less (95% CI 2-4%), and 23% less (95% CI 22-24%), respectively, compared with levels in non-smokers. At comparable maternal ages, women who smoked cigarettes were identified as being at high risk for fetal Down syndrome 40% less often than non-smokers (4.0 versus 7.1% at a risk level of 1:250). Adjusting hCG levels for smoking status reduced the overall false-positive rate from 6.4 to 6.1% (using a term risk cutoff level of 1:250). The predicted effect on detection was small (a 0.7% increase). The prevalence of Down syndrome was lower among smokers, but the difference was not statistically significant (odds ratio 0.51, 95% CI 0.15-1.5).

CONCLUSIONS

Adjusting the serum markers used for Down syndrome screening for the effect of maternal smoking has a small effect on overall screening performance. Given the uncertainty over whether there is a lower birth prevalence among women who smoke cigarettes, such adjustment is not currently justified.

Simultaneous fetal and maternal cotinine levels in pregnant women smokers

OBJECTIVE

Our purpose was to determine the simultaneous concentrations of serum cotinine in both fetal and maternal blood.

STUDY DESIGN

Serum cotinine levels were measured in 11 maternal-fetal pairs at percutaneous umbilical blood sampling. Statistical analysis was performed by means of a one-group t test to determine whether the ratio of fetal-to-maternal cotinine was significantly different from 1.

RESULTS

Fetal cotinine levels ranged from 75% to 110% of maternal values (mean ratio 0.90, 95% confidence interval 0.83 to 0.97). Fetal levels were significantly lower than maternal concentrations (p = 0.02).

CONCLUSIONS

Cotinine, a metabolite of nicotine used to quantify exposure to tobacco smoke, readily gains access to the fetal circulation. Fetal cotinine concentrations in pregnant women smokers are, on average, 90% of maternal values throughout gestation.

Primary staphylococcal pneumonia in childhood: a review of 69 cases

Primary staphylococcal pneumonia is a rapidly progressive illness with well-described clinical and radiological features and a significant mortality rate. This retrospective study of cases diagnosed over a 20 year period at a tertiary paediatric hospital was undertaken to document the epidemiology and assess the management and mortality of the disease. The survey demonstrated that far fewer patients are being seen than formerly and confirmed that this is a disease primarily affecting infants and Aboriginal children. The initial radiological features were not diagnostic in the majority of cases but typical changes appeared in most at some time during the illness. The use of surgical drainage was not associated with a decrease in the duration of fever or length of hospital stay. The mortality rate has improved but remains significant.

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

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

Prenatal screening for Down's syndrome with use of maternal serum markers

BACKGROUND

Approximately 35 percent of all cases of Down's syndrome in fetuses can be detected by measuring maternal serum alpha-fetoprotein during the second trimester in the general population of pregnant women. Recent case-control studies indicate that this detection rate could be approximately doubled by measuring serum levels of unconjugated estriol and chorionic gonadotropin, which are abnormally low and abnormally high, respectively, in women carrying fetuses affected by Down's syndrome.

METHODS

We prospectively screened 25,207 women and adolescents in the second trimester of pregnancy and assigned each a risk of fetal Down's syndrome with an algorithm that took into account measurements of all three serum markers in combination with maternal age. On this basis, 1661 subjects (6.6 percent) were initially assigned a second-trimester risk of fetal Down's syndrome of at least 1 in 190, and 962 (3.8 percent) were offered amniocentesis for chromosomal analysis after verification of gestational age. Gestational age was determined on the basis of the first day of the last menstrual period or, when available, by ultrasonography.

RESULTS

Among the 760 women and adolescents who chose amniocentesis, 20 cases of fetal Down's syndrome were detected, along with 7 other chromosomal disorders. There was 1 additional case of fetal Down's syndrome among the 202 women who chose not to have amniocentesis. The rate of detection of Down's syndrome was thus 58 percent (21 of 36 expected cases), and the frequency of identifying a fetus with Down's syndrome in women undergoing amniocentesis was 1 per 38 amniocenteses (95 percent confidence interval, 1 in 25 to 1 in 62).

CONCLUSIONS

Measuring serum alpha-fetoprotein, chorionic gonadotropin, and estriol is more effective in screening for fetal Down's syndrome than measuring maternal serum alpha-fetoprotein alone. Such an expanded protocol can readily be incorporated into existing prenatal screening programs.

Single daily dose ceftriaxone therapy in epiglottitis

Ceftriaxone as a single daily intravenous dose for 5 days was used to treat seven patients with proven Haemophilus influenzae epiglottitis. All children responded favourably. The serum levels achieved exceeded the MIC by up to 1500 times at the trough level during and for up to 24 h after the completion of the treatment. Side effects were mild and transient and did not disrupt the continuity of the treatment. Ceftriaxone potentially offers a number of clinical and economic advantages in the management of epiglottitis.

An unsuccessful cotinine-assisted intervention strategy to reduce environmental tobacco smoke exposure during infancy

OBJECTIVE

To test a low-intensity physician's office-based intervention strategy using infant urine cotinine measurements, aimed at reducing infant exposure to environmental tobacco smoke.

DESIGN

A randomized intervention trial.

SETTING

Offices of 28 physicians (pediatricians and family practitioners) and two hospital-based clinics in the Greater Portland, Me, area.

PARTICIPANTS

Infants brought to the physician by a parent (usually the mother) for an initial well-child visit. A total of 518 of these infants and their mothers consented to provide information about household smoking habits and to provide a sample of the infant's urine for biochemical analysis.

SELECTION PROCEDURE

From among the consecutive sample of 518 enrolled mother/infant pairs, 103 mothers reported that they smoked 10 or more cigarettes per day, and these were randomized on an individual basis for intervention (52 pairs) or control (51 pairs). Randomization took place at the study center when the infant's urine sample and information about household smoking habits were received.

INTERVENTION

The physician telephoned the mother to report the urine cotinine result and to explain its meaning. The physician then signed and sent an individualized form letter to the mother, providing specific recommendations for changing household smoking habits.

RESULTS

Follow-up urine cotinine measurements were obtained in 27 (52%) of 52 infants from the intervention group and in 29 (57%) of the 51 controls 2 months later. The mean log ratio of the follow-up to initial urine cotinine measurements was 6% lower in the intervention group than in the control group. This difference was not statistically significant.

CONCLUSION

The low-intensity intervention strategy did not significantly influence infant exposure to environmental tobacco smoke in the household.

Self-rated physical activity level during the second trimester and pregnancy outcome

To examine the relationship between level of physical activity during pregnancy and subsequent pregnancy outcome, we asked women enrolling for maternal serum alpha-fetoprotein (MSAFP) screening in Maine during the years 1984-1988 to rate their usual physical activity level as light, moderate, or vigorous. Overall, 23,091 women were approached and 21,342 (92%) responded. Ten percent rated their physical activity level as light, 84% as moderate, and 6% as vigorous. Those who identified their physical activity level as vigorous were, on average, slightly older and more educated, and weighted less than women in the other two categories. However, there were no significant differences in the rates of low birth weight or fetal or neonatal death.

Lack of an association between late fetal death and antiphospholipid antibody measurements in the second trimester

To examine the relationship between elevated antiphospholipid antibody levels in the maternal circulation and late fetal death, we carried out a case-control study in which levels of anticardiolipin and antiphosphatidylserine antibodies were measured in banked second-trimester sera from 309 pregnancies ending in fetal death and from 618 viable control pregnancies. The sera were obtained from a population base of approximately 22,000 pregnancies enrolled for maternal alpha-fetoprotein screening between 15 and 20 weeks' gestation. The anticardiolipin immunoglobulin G level was markedly elevated (15.6 SD) in one serum sample associated with a fetal death. Otherwise, the anticardiolipin and antiphosphatidylserine measurements were similar in the two populations. Several other factors known to be associated with fetal death were also examined, and these all demonstrated the expected relationship. Antiphospholipid antibody measurements obtained at 15 weeks' gestation or later in the general pregnancy population are not helpful in identifying pregnancies at risk for fetal death.

Cotinine-assisted intervention in pregnancy to reduce smoking and low birthweight delivery

OBJECTIVE

To investigate the feasibility and impact of integrating a cotinine-assisted smoking intervention programme with an existing antenatal maternal serum alpha-fetoprotein (AFP) screening service for open neural tube defects.

DESIGN

A multisite randomized controlled trial.

SETTING

139 physician offices and clinic sites in Maine providing antenatal care.

SUBJECTS

2848 pregnant women who smoked 10 or more cigarettes daily, enrolled at between 15 and 20 weeks gestation, from a population base of approximately 18,000 pregnancies.

INTERVENTIONS

The women were individually allocated at random to intervention or control groups within each centre at the time the serum sample was received for AFP measurement. The intervention group received an interpreted measurement of the serum cotinine, reported through the physician to the woman, along with a self-help smoking cessation booklet and a repeat serum cotinine measurement one month later, again interpreted and reported through the physician to the woman. Women in the control group received the usual anti-smoking advice provided by the antenatal care site and were not told of the study.

MAIN OUTCOME MEASURES

Birthweight, physician cooperation with study protocol (as measured by effectiveness in obtaining repeat serum samples for cotinine measurements).

RESULTS

Pregnancy outcome data were available for 97% of the study population, including birthweight for 2700 singleton viable pregnancies. The smoking intervention programme led to a significant 66 g increase in mean birthweight (P = 0.03; 95% CI+9 to +123 g) and to a 30% reduction in the rate of low birthweight in pregnancies managed by the 70 physicians who secured the highest rate of obtaining repeat serum samples for cotinine measurements in their intervention group. Among the remaining 69 physicians, intervention had no detectable effect on birthweight.

CONCLUSION

A cotinine-assisted smoking intervention programme managed from a central location as an adjunct to a maternal serum AFP screening service can, with the cooperation of physicians responsible for antenatal care, lead to a significant and cost-effective reduction in the number of low birthweight babies. This programme is inexpensive, requires little extra effort, and does not need specially trained personnel.

Second-trimester levels of maternal serum unconjugated oestriol and human chorionic gonadotropin in pregnancies affected by fetal anencephaly and open spina bifida

Unconjugated oestriol (uE3) and human chorionic gonadotropin (hCG) levels were determined in second-trimester maternal serum (MS) samples from 21 pregnancies associated with fetal anencephaly and 15 pregnancies associated with fetal open spina bifida. Each measurement was expressed as a multiple of the median (MoM) for unaffected pregnancies for each completed week of gestation. In pregnancies associated with anencephaly, the median value for MSuE3 was very low (0.17 MoM, range less than 0.12-0.33 MoM), suggesting a functional defect in the fetal adrenal prior to 20 weeks' gestation; the median value for MShCG was also low (0.73 MoM), although not to the same extent as for MSuE3. A biological explanation for the hCG result is not apparent. In pregnancies associated with open spina bifida, the MSuE3 and MShCG values were unremarkable, consistent with a lack of involvement of these open fetal defects in the synthesis and secretion of uE3 and hCG.

Environmental tobacco smoke exposure during infancy

We collected information about household smoking habits from 518 mothers when they made their first well child visit with a 6 to 8-week old infant. A urine sample was also collected from the infant, the cotinine concentration measured, and the measurement correlated with data provided by the mother. Eight percent of the infant urine cotinine values fell at or above 10 micrograms/L in the 305 households where no smoking was reported. Corresponding rates were 44 percent in the 96 households where a member other than the mother smoked, 91 percent in the 43 households where only the mother smoked, and 96 percent in the 74 households where both the mother and another household member smoked. In households where the mother smoked, infant urine cotinine levels were lower in the summer, and higher when the infant was breast-fed. A screening question about family smoking habits in conjunction with well child care could effectively define a group of infants exposed to environmental tobacco smoke and thus be at greater risk for respiratory diseases.