Are our Babies Becoming Bigger?

I have tried to show, using a contemporary international data set, the overall consistency in shape of curves of national birthweight distributions which reflect the biological and social characteristics of the population from which they are derived, and the effects of changes in these characteristics. For several countries, including the United States and England and Wales, the trends in recent years have been such as to shift the main distribution upwards, so that the median weight has increased.

Also shown has been the close and specific relationship within each population group between infant mortality and birthweight, with sharp falls of mortality with increasing birthweight. It has been shown elsewhere that similar patterns are seen with short- and long-term morbidity, thus underlining the importance to be attached to increasing birthweight particularly in underprivileged groups. In the short term this can be done by reducing the frequency of parental smoking, where this is a problem, and in the longer term by improving maternal health and nutrition. The shift towards higher birthweights if it persists, should make an important contribution towards the improvement of the public health of the next generation.

Cytological and epidemiological findings in trisomies 13, 18, and 21: England and Wales 2004-2009

This study describes the cytological and epidemiological findings in 985 trisomy 13 and 2512 trisomy 18 compared with 10,255 trisomy 21 diagnoses between 2004 and 2009 included in the National Down Syndrome Cytogenetic Register of England and Wales. The frequency of occurrence, proportions diagnosed prenatally, sex ratios, mean maternal age, and proportions of mothers with recurrences were analyzed. Ninety-seven, 98%, and 92% were free karyotypes for trisomy 21, 18, and 13, respectively; 3% of 21, 1% of 18, and 8% of trisomy 13 were translocations; and under 1% of trisomies 21 and 18 were double or triple aneuploids. Overall 1% of each trisomy had mosaicism, but 48% of the trisomy 21 double aneuploids, and 10% of trisomy 18 multiple aneuploids had mosaicism. The proportion of livebirths was 40% of trisomy 21, 11% of 18, and 13% of 13, respectively. Free trisomies 21 and 13 had an excess of males, and 18 had an excess of females, as did mosaic free trisomies 21 and 18. Mean maternal ages were 35.9 years in trisomy 21, 36.4 years in 18, and 34.6 years in 13. During the 6 years of data collection 1% of the mothers had recurrences, most recurrent trisomy 21 or 18 were identical translocations, but hetero-trisomic recurrences included 21 and 18, and 21 and 13. There are significant differences between the trisomic karyotypes and attributes, possibly related to their variable origins. Notable are the relative excess of trisomy 13 translocations, mosaicism in cases with multiple aneuploidy, and the types of homo- and hetero-recurrences.

Cytogenetic and epidemiological findings in Down syndrome: England and Wales 1989-2009

This study describes the characteristics of karyotypes leading to phenotypic Down syndrome (trisomy 21) in 29,256 cases diagnosed between 1989 and 2009 in England and Wales included in the National Down Syndrome Cytogenetic Register (NDSCR). The frequency of occurrence of the different karyotypes, proportions diagnosed prenatally, sex ratios, mean maternal age, and proportions of mothers with recurrences were analyzed. Nearly 97% of all cases were free trisomy 21; 2.9% contributory trisomy 21, 0.3% double or triple aneuploidies; 1% of all were mosaics. Mean maternal age of free trisomy 21 cases was 35 years, 54% were male, and 1% of mothers had recurrences. Free trisomy 21 mosaics had a lower mean maternal age (33 years), a lower proportion of males (39.5%), and 2.5% of mothers had recurrences. The majority of contributory translocations were Robertsonian or rea (21;21). Their mothers were younger, particularly those of Robertsonian translocations (28 years). Of the Robertsonian der (14;21) translocations of known parental origin, 54% were de novo, 41% maternal and 5% paternal and 15.8% of mothers of those of maternal origin had recurrences. Multiple aneuploidies have the highest proportion of males (67%), highest proportion of mosaics (40%), a mean maternal age of 37 years, and no mothers had a recurrence. The size of this national register allowed the frequency of occurrence of the rarer karyotypes of Down syndrome to be estimated and their epidemiology described.

Down's syndrome: screening and antenatal diagnosis regionally in England and Wales 1989–2008

Objective

To illustrate regional changes that occurred in screening for Down's syndrome (trisomy 21) in England and Wales from 1989 to 2008.

Methods

The National Down Syndrome Cytogenetic Register has collected data on all ante- and postnatal diagnoses of Down's syndrome in England and Wales since 1989 ( n = 27,954). The percentages of (i) diagnoses made antenatally, (ii) antenatal diagnoses that had nuchal translucency (NT) measured, and (iii) antenatal diagnoses in mothers aged 37 and over with advanced maternal age as the sole recorded indication for diagnosis are presented according to where the mother lived (Government Office Region), year of diagnosis (1989–1994, 1995–2000, 2001–2006, 2007–2008), and maternal age (<37 years, ≥37 years).

Results

The percentage of cases diagnosed antenatally has increased in younger women but varies between regions. It remained relatively constant at approximately 70% in older women. The use of NT measurement in antenatal screening has expanded rapidly but varies regionally, being most common in London and the South East where, in 2007–2008, over 75% of antenatal diagnoses in older women had NT measured. The sole indication of advanced maternal age has substantially reduced, and was less than 10% in older mothers in all regions in 2007–2008.

Conclusions

There are regional and maternal age variations in Down's syndrome screening and diagnosis. Some regions used NT measurements, and eliminated advanced maternal age as sole reason for antenatal diagnostic testing more quickly than others. The reasons for variations need to be identified and addressed to ensure that when new screening techniques become available, regional differences are minimized.

Trends in Down's syndrome live births and antenatal diagnoses in England and Wales from 1989 to 2008: analysis of data from the National Down Syndrome Cytogenetic Register

OBJECTIVES

To describe trends in the numbers of Down's syndrome live births and antenatal diagnoses in England and Wales from 1989 to 2008. Design and setting The National Down Syndrome Cytogenetic Register holds details of 26488 antenatal and postnatal diagnoses of Down's syndrome made by all cytogenetic laboratories in England and Wales since 1989.

INTERVENTIONS

Antenatal screening, diagnosis, and subsequent termination of Down's syndrome pregnancies.

MAIN OUTCOME MEASURES

The number of live births with Down's syndrome.

RESULTS

Despite the number of births in 1989/90 being similar to that in 2007/8, antenatal and postnatal diagnoses of Down's syndrome increased by 71% (from 1075 in 1989/90 to 1843 in 2007/8). However, numbers of live births with Down's syndrome fell by 1% (752 to 743; 1.10 to 1.08 per 1000 births) because of antenatal screening and subsequent terminations. In the absence of such screening, numbers of live births with Down's syndrome would have increased by 48% (from 959 to 1422), since couples are starting families at an older age. Among mothers aged 37 years and older, a consistent 70% of affected pregnancies were diagnosed antenatally. In younger mothers, the proportions of pregnancies diagnosed antenatally increased from 3% to 43% owing to improvements in the availability and sensitivity of screening tests.

CONCLUSIONS

Since 1989, expansion of and improvements in antenatal screening have offset an increase in Down's syndrome resulting from rising maternal age. The proportion of antenatal diagnoses has increased most strikingly in younger women, whereas that in older women has stayed relatively constant. This trend suggests that, even with future improvements in screening, a large number of births with Down's syndrome are still likely, and that monitoring of the numbers of babies born with Down's syndrome is essential to ensure adequate provision for their needs.

Main causes of major mental handicap: prevalence and epidemiology

The prevalence of educational subnormality of a severe form (between 3 and 3.6 per thousand children of school age) and the prevalence of cerebral palsy (between 2 and 2.4 per thousand) have been fairly stable up to recent years. This stability has also applied to the relative proportions of the different major causes contributing to the handicaps. Where the ascertainment of such conditions is good, their prevalence monitored and the life expectancy of affected individuals estimated, any changes in prevalence can be used to measure the effectiveness of new forms of prevention, or alternatively to indicate the existence of new environmental hazards. Only a multi-pronged campaign against many of the recognized causes will have a substantial impact on prevalence.

The proportions of Down's syndrome pregnancies detected prenatally in England and Wales from 1989 to 2004

OBJECTIVES

The proportion of Down's syndrome pregnancies detected prenatally in England and Wales is lower in younger mothers than in older mothers. This paper examines the reasons for this apparent age inequality.

METHODS

We used data from the National Down Syndrome Cytogenetic Register (NDSCR) to examine the time trend of the proportion of Down's syndrome pregnancies diagnosed prenatally according to maternal age over the years 1989-2004 in England and Wales.

RESULTS

A lower proportion of younger mothers had their Down's syndrome pregnancy detected prenatally than older mothers; however, this gap has been closing over time. For example, for mothers under 25 years of age only 13% of Down's syndrome pregnancies were detected prenatally from 1989 to 1992, with this figure rising to 34% in 2001-2004, compared with proportions of 74% in both periods for mothers over 44 years of age. A lower uptake of screening among younger women could not explain these differences. The differences in detection rates of the screening methods according to maternal age, particularly of the older screening tests, could account for these differences.

CONCLUSIONS

The closing gap between the proportions of younger and older women having their affected pregnancy prenatally diagnosed is a confirmation of the improvement of screening methods over time.

Maternal age-specific fetal loss rates in Down syndrome pregnancies

OBJECTIVES

Pregnancies affected by Down syndrome (DS) have a greater risk of spontaneous fetal loss than those that are unaffected. In this article, we investigate the relationship between maternal age and the risk of spontaneous fetal loss in DS pregnancies.

METHODS

Fetal loss at different maternal ages were estimated by survival analysis using follow-up of 5177 prenatally diagnosed cases. The maternal age effect on loss rate was subsequently confirmed by a re-analysis of published comparisons of the maternal age-specific prevalence of DS at different gestational ages.

RESULTS

The average fetal loss rate between the time of chorionic villus sampling (CVS) and term was 32% (95% CI: 26-38), increasing from 23% (95% CI: 16-31) for women aged 25 to 44% (33-56) for women aged 45. The average fetal loss rate between the time of amniocentesis and term was 25% (21-31), increasing from 19% (14-27) to 33% (26-45) across the same age range.

CONCLUSION

The fetal loss rate in DS pregnancies increases with maternal age, and this has consequences when estimating the live birth prevalence of DS in the presence of prenatal diagnosis and termination, and when assessing the performance of prenatal screening techniques.

Triploidy identified through second-trimester serum screening

OBJECTIVES

To describe the maternal serum marker patterns of triploid pregnancies and estimate the second-trimester prevalence of triploidy.

METHODS

Forty-two cases of triploidy were identified in six serum screening programmes, five in the United Kingdom, one in Canada. This study describes the serum marker patterns, serum screening results for Down syndrome, trisomy 18 and open neural tube defects, and maternal age of these triploidy cases. The risk cut-off levels were > or = 1 in 250 for Down syndrome, > or =2.5 MoMs alpha-fetoprotein for open neural tube defects and > or =1:100 for trisomy 18 screening. The estimated second-trimester prevalence of triploidy was based on 22 triploidy cases ascertained in 599 934 pregnancies from three routine screening programmes, which attempted complete ascertainment of aneuploidy cases.

RESULTS

The observed second-trimester rate of triploidy was 0.37 per 10 000 fetuses. Two different serum marker patterns were seen in triploid pregnancies, distinguished from each other by typically very high or very low levels of total hCG or free beta-hCG. The median maternal ages were respectively 33 years for triploidy with human chorionic gonadotrophin levels < 1.0 MoM, and 26 years for those with hCG levels > or =1.0 MoM. Fifty-seven percent of the pregnancies with a triploid fetus had a risk estimate > or =1:100 for trisomy 18 alone, 10% had an alpha-fetoprotein > or =2.5 MoM, 5% were screen positive for Down syndrome alone, and 19% had an increased risk or positive results for more than one anomaly.

CONCLUSION

The simultaneous use of maternal serum tests designed to screen prenatally for Down syndrome, neural tube defects, and an increased risk of trisomy 18 resulted in a screen-positive result for 90% of pregnancies with triploidy.

Recurrences of free trisomy 21: analysis of data from the National Down Syndrome Cytogenetic Register

OBJECTIVES

To determine the recurrence risk of a free trisomy 21 pregnancy.

METHODS

Data from the National Down Syndrome Cytogenetic Register (NDSCR), which contains information on nearly all cases of Down syndrome between 1989 and 2001 in England and Wales were used. Among 11 281 women with a Down syndrome pregnancy who had had at least one previous pregnancy there were 95 women who had had a previous Down syndrome pregnancy.

RESULTS

Women who have had a previous Down syndrome pregnancy have a constant absolute excess risk above their maternal age-related risk of having a subsequent affected pregnancy. This absolute excess risk is determined by the age at which the affected pregnancy occurred and is higher for younger than for older women. For example, after a Down syndrome pregnancy at age 20, this excess is 0.62% (95% CI: 0.24 to 1.15%) at early second trimester, and, after one at age 40, it is 0.04% (95% CI: 0.01 to 0.07%).

CONCLUSION

More precise risk estimates by single year of maternal age for use in genetic counselling are provided, but they need validation from other studies before they are incorporated in the risk estimation routines used in Down syndrome screening programmes.

Risk of a Down syndrome live birth in women 45 years of age and older

OBJECTIVES

To determine the risk of a Down syndrome (DS) live birth for women 45 years of age and over.

METHODS

A meta-analysis of data from five published articles, 13 EUROCAT congenital anomaly population registers and two unpublished sources.

RESULTS

Information was available on the number of DS live births occurring amongst 13,745 live births to women 45 years of age and over. Information was also available on DS pregnancies diagnosed prenatally that were subsequently terminated. These pregnancies were adjusted for expected fetal loss to estimate the number of live births that would have occurred in the absence of prenatal diagnoses, when a total of 471 DS live births were estimated to have occurred. The risk of a DS birth did not increase for women 45 years of age and over. The average risk was 34 per 1000 births (95% CI: 31-37).

CONCLUSION

The risk of a DS live birth for women 45 years of age and over is considerably lower than has often been previously assumed. The most likely explanation is that women of this age are more likely to miscarry DS pregnancies than younger mothers.

Prenatal screening for Down syndrome in England and Wales and population-based birth outcomes

OBJECTIVE

Whether the introduction of antenatal screening for Down syndrome in England and Wales with serum biochemistry or ultrasound has led to improvements in patient outcomes is unknown. The purpose of this study was to relate pregnancy outcomes to the dominant method used for prenatal Down syndrome screening.

STUDY DESIGN

For the years 1989 through 1999, England and Wales were divided into geographically defined areas where specific hospitals, health authorities, and cytogenetic laboratories provided maternity care for well-defined populations. For each year from 1989 through 1999, the dominant Down syndrome screening method that was used in each area was determined. Outcomes for area-years that used serum biochemistry or ultrasound (first or second trimester) were compared with area-years that used advanced maternal age as the dominant screening method. The percent of Down syndrome cases that were diagnosed prenatally (effectiveness) and the number of invasive prenatal tests that were performed to diagnose each Down syndrome case prenatally (efficiency) were compared.

RESULTS

There were 5,980,519 births and 335,184 referrals for prenatal karyotyping (amniocentesis and chorionic villus sampling) that occurred in the area-years studied, of which 12,047 pregnancies were diagnosed as Down syndrome; 5393 cases of Down syndrome (45%) were diagnosed prenatally. Invasive testing increased from 4.4% of pregnancies in 1989 to 6.4% in 1997 and declined slightly in 1999 (5.8%). Prenatal diagnosis of Down syndrome cases rose from 28% in 1989 to 53% in 1999, and the number of invasive tests that were performed to diagnose each Down syndrome case fell from 89.7 to 47.7 (P [for trend]<.0001). Areas with serum or ultrasound as the dominant screening method detected 50% more Down syndrome cases in prenatally (52% and 53% vs 36%; P<.0001) and performed fewer invasive procedures to diagnose each Down syndrome case (60.7 and 52.0 vs 88.0; P<.0001) compared with areas in which advanced maternal age screening was dominant, despite serving populations with similar mean/median maternal ages.

CONCLUSION

In clinical practice, screening programs for Down syndrome that were based on maternal serum biochemistry or ultrasound were more effective and efficient than the screening programs that used advanced maternal age alone.

Using Down syndrome serum screening results to predict low birthweight

OBJECTIVE

To investigate the use of prenatal maternal serum screening results for Down syndrome, for the prediction of low (<2500 g) and very low (<1500 g) birthweight.

DESIGN

Record linkage of maternal serum screening results with the corresponding birth records.

PARTICIPANTS

42 259 women whose pregnancies had been screened for the risk of Down syndrome.

SETTING

Three East London maternity units, between February 1989 and August 1998.

RESULTS

Estimates were made of the effectiveness of single markers only for the prediction of low birthweight, and of multiple markers together with mother's weight and smoking habit. As reported previously, high levels of the single markers alpha-fetoprotein and total human chorionic gonadotrophin, inhibin A, and low levels of unconjugated oestriol were associated with low birthweight. However, the best prediction was obtained when multiple serum markers comprising alpha-fetoprotein, unconjugated oestriol, and inhibin A were used in combination together with mother's weight and adjustment for smoking habit. For a false-positive rate of 5%, this combination predicted 23% of low birthweight and 39% of very low birthweight babies, possibly the best method of prediction to date.

CONCLUSION

Prediction of low birthweight derived from Down syndrome screening could be used, for little extra cost, to advise on place of delivery or to select candidates for randomised clinical trials of low birthweight prevention.

Comparison of models of maternal age-specific risk for Down syndrome live births

OBJECTIVES

To display and compare the different published formulae that specify the association between maternal age and the risk of a Down syndrome live birth.

METHODS

Papers published since 1987 on the prevalence of Down syndrome live births in relation to maternal age were located using MEDLINE and the references given in other papers. The data series and the models fitted to them were plotted to obtain a visual idea of their similarities and differences.

RESULTS

The observed and modelled age-specific rates for Down syndrome births were remarkably similar in all published series of data for women up to the age of 35, were reasonably similar for women aged 35 to 45, but differed for women older than 45.

CONCLUSION

In practice, the overall small differences in age-related risk between the different studies did not materially affect the performance of antenatal screening for Down syndrome. If a choice is to be made, the analysis based on the National Down Syndrome Cytogenetic Register (NDSCR) has marginal advantages since it is based on the largest data set and the corresponding model fits the data well. More data is needed to clarify the pattern of risk with maternal age among women over 45 years of age.

The use of record linkage for auditing the uptake and outcome of prenatal serum screening and prenatal diagnostic tests for Down syndrome

OBJECTIVES

To pilot the use of linked routine records for auditing Down syndrome prenatal serum screening and diagnostic tests.

METHODS

The cohort studied were 110 272 patients of 4 London maternity units that offered the Bart's maternal serum tests any time between 1990 and 1999. Audit was based on linked data derived from obstetric records, referral data on maternal serum screening and/or prenatal diagnoses. Cytogenetic reports without matching obstetric data were retained in the cohort as they included fetal deaths or terminations.

RESULTS

(1) Significant independent influences on uptake of serum screening (58% overall) were maternal age, ethnicity, year and referring hospital, and those on uptake of prenatal diagnosis (4% overall) were screening result (54% uptake after positive screen), maternal age, year and referring hospital; (2) detection, false-positive rates and odds of being affected after positive results were respectively 49%, 4% and 1 : 59 between 1990 and 1994, and 78%, 7% and 1 : 58 after 1994. Using maternal age alone (cut-off > or =37 at delivery), these would have been respectively 40%, 7% and 1 : 96 between 1990 and 1994, and 40%, 9% and 1 : 107 between 1995 and 1999.

CONCLUSIONS

Ongoing audit of DS prenatal programmes could be derived from computerised maternity data sets if they included fetal deaths, and relevant laboratory and ultrasound findings.

Revised estimates of the maternal age specific live birth prevalence of Down's syndrome

OBJECTIVES

To revise the estimates of maternal age specific live birth prevalence of Down's syndrome in the absence of antenatal screening and selective termination using newly available data.

SETTING AND DESIGN

Data were used from the National Down Syndrome Cytogenetic Register (NDSCR), which contains information on nearly all antenatally or postnatally diagnosed cases of Down's syndrome in which a karyotype was confirmed between 1989 and 1998 in England and Wales. It is the largest single series of data on the prevalence of Down's syndrome.

RESULTS AND CONCLUSION

The prevalence does not continue increasing at an increasing rate with age above age 45 as has been previously assumed. Above this age the rate of increase declines with increasing age. The overall age pattern is sigmoidal. A new logit logistic model is proposed which fits the data well. The risk of a Down's syndrome live birth is given by: risk=1/(1+exp(7.330-4.211/(1+exp(-0.282x(age-37.23))))).

Mortality and cancer incidence in persons with numerical sex chromosome abnormalities: a cohort study

Mortality and cancer incidence were assessed in a cohort of 1373 patients with numerical sex chromosome abnormalities diagnosed at three cytogenetics centres in Britain during 1959-90, and were compared with expectations from national rates. Four hundred patients with Turner's syndrome were followed, of whom 62 died, with a relative risk (RR) of death of 4.16 (95% confidence interval (CI) 3.22-5.39). Turner's syndrome patients had greatly raised risks of death from diseases of the nervous, cardiovascular, respiratory, digestive and genitourinary systems. One hundred and sixty three deaths occurred among 646 patients with Klinefelter's syndrome with a 47,XXY constitution, giving an RR of 1.63 (1.40-1.91). Mortality in these patients was significantly raised from diabetes and diseases of the cardiovascular, respiratory and digestive systems. There was also significantly increased mortality for patients with X polysomy (RR = 2.11 (1.43-3.02)) and Y polysomy (RR = 1.90 (1.20-2.85)), the former with significantly increased mortality from cardiovascular disease and the latter from respiratory disease. The only significantly raised risks of cancer incidence or mortality in the cohort were for lung cancer and breast cancer in patients with Klinefelter's syndrome with a 47,XXY constitution, and non-Hodgkin's lymphoma in men with more than three sex chromosomes.

Mortality and cancer incidence in persons with Down's syndrome, their parents and siblings

A cohort study of 1425 persons with Down's syndrome (DS), and of their parents (447 mothers, 435 fathers) and siblings (1176), was set up to investigate death rates from various causes and cancer incidence patterns. In individuals with DS the all-cause death rate was six times that of the national population (SMR = 622: 95% CI 559-693), the excess being attributable to many different causes. These included: leukaemia (SMR = 1304: 95% CI 651-2334); diabetes mellitus (SMR = 982: 95% CI 267-2515); Alzheimer's disease (SMR = 22028: 95% CI 7137-51326); epilepsy (SMR = 1727: 95% CI 744-3403); and congenital anomalies (SMR = 4987: 95% CI 4175-5955). The overall survival showed marked improvements for successive birth cohorts, particularly at young ages. For mothers and fathers of persons with DS, all-cause death rates were 20% lower than national rates and there were no significant excesses from any specific cause. For siblings, all-cause death rates were similar to national rates; the only condition with a significantly raised mortality ratio was colo-rectal cancer (SMR = 793: 95% CI 216-2031), but this may well be a chance finding.

Socioeconomic inequalities in risk of congenital anomaly

AIMS

To investigate socioeconomic inequalities in the risk of congenital anomalies, focusing on risk of specific anomaly subgroups.

METHODS

A total of 858 cases of congenital anomaly and 1764 non-malformed control births were collected between 1986 and 1993 from four UK congenital malformation registers, for the purposes of a European multicentre case control study on congenital anomaly risk near hazardous waste landfill sites. As a measure of socioeconomic status, cases and controls were given a value for the area level Carstairs deprivation index, by linking the postcode of residence at birth to census enumeration districts (areas of approximately 150 households).

RESULTS

Risk of non-chromosomal anomalies increased with increasing socioeconomic deprivation. The risk in the most deprived quintile of the deprivation index was 40% higher than in the most affluent quintile. Some malformation subgroups also showed increasing risk with increasing deprivation: all cardiac defects, malformations of the cardiac septa, malformations of the digestive system, and multiple malformations. No evidence for socioeconomic variation was found for other non-chromosomal malformation groups, including neural tube defects and oral clefts. A decreasing risk with increasing deprivation found for all chromosomal malformations and Down's syndrome in unadjusted analyses, occurred mainly as a result of differences in the maternal age distribution between social classes.

CONCLUSION

Our data, although based on limited numbers of cases and geographical coverage, suggest that more deprived populations have a higher risk of congenital anomalies of non-chromosomal origin and some specific anomalies. Larger studies are needed to confirm these findings and to explore their aetiological implications.

National Confidential Enquiry into counselling for genetic disorders by non-geneticists: general recommendations and specific standards for improving care

OBJECTIVES

To assess genetic counselling by non-geneticists and to improve clinical practice.

DESIGN

National retrospective review of casenotes.

SETTING

Antenatal, paediatric, medical, and surgical units.

SAMPLE

1293 genetic events were identified, involving potentially avoidable cases of Down's syndrome, neural tube defect, cystic fibrosis, beta thalassaemia major and late onset medullary carcinoma of the thyroid (multiple endocrine neoplasia). Notes were available for review in 888 (69%) of these cases.

OUTCOMES

Documented counselling, offers of relevant genetic screening and prenatal diagnosis.

RESULTS

Clinical audit was frustrated by poor quality hospital records lacking evidence of counselling. Non-geneticist clinicians concentrate on the management of disease, and may overlook the need for counselling and recording data which patients will later need for decisions about reproduction or disease prevention. Counselling, screening and prenatal diagnosis were sometimes impossible because of late booking in pregnancy, or because of delayed diagnosis of an earlier affected child with cystic fibrosis. There are marked regional inequalities of access to genetic services, particularly for minority ethnic groups with increased risks of thalassaemia. Although patients were selected for this enquiry because they had known high risks of genetic disorders, on average less than half were referred to medical geneticists. General recommendations relevant for improvement of care for patients and families with medical genetic needs and those specific for each disorder are given.

CONCLUSIONS

Assessment of the quality of genetic care becomes increasingly important as genetic counselling spreads beyond the narrow confines of specialist genetic services. Even though the events studied in this enquiry largely occurred between 1991 and 1995, there is little reason to believe that clinicians in general have become markedly better trained in medical genetics. The General Medical Council and Medical Royal Colleges should urgently consider the need for a national policy for improving undergraduate and postgraduate medical, nursing and midwifery education in genetics. Commissioners of clinical services should require that genetic management be at least as well-documented as surgical operations, drug records and informed consent, perhaps by using a nationally agreed pro-forma for prenatal diagnosis. Regular audit of counselling provided by non-geneticists is necessary to confirm that clinical improvements are occurring and standards are being met. The Confidential Enquiry provides data for a systematic approach to clinical governance of genetics in all specialities. This sets the scene for multi-speciality NHS genetic services capable of giving patients greater consistency both in access and in quality.

Intergenerational influences affecting birth outcome. II. Preterm delivery and gestational age in the children of the 1958 British birth cohort

The 1958 British cohort study has data to investigate intergenerational effects on preterm delivery and on gestational age in non-preterm births, allowing for many confounders that may differ in the more pathological preterm babies. Previous results for all gestational ages-have been inconsistent. The strongest and only likely independent intergenerational effect on non-preterm gestational age found is parental gestational age (adjusted regression coefficient = 0.067 weeks per week in mothers and 0.045 in fathers). The preterm analysis has low power; however, reported history of hypertension in mothers (any), in fathers and in the maternal grandmother (measured in the 1958 pregnancy) all significantly and independently increased the risk of preterm birth [OR = 1.7, 2.0, 1.5 respectively]. The absolute risk was particularly high in hypertensive mothers who had been preterm themselves (21%). Other possible intergenerational influences of height, weight, fetal growth and gestation were not significant enough and/or consistent enough between parents to speculate whether they are truly intergenerational or confounded by other factors acting during the pregnancy. Excepting mother's weight for height, no genetic or environmental influence studied affects both gestational age and fetal growth in term births. However, many maternal factors that reduce either fetal growth or gestation in term births are associated with increased risk of preterm birth.

Intergenerational influences affecting birth outcome. I. Birthweight for gestational age in the children of the 1958 British birth cohort

There is considerable literature on intergenerational influences on birthweight. Few studies have been able to investigate such influences on the more basic measures of birthweight for gestational age and gestational age itself. This paper considers fetal growth. The investigations are derived from the 1958 British birth cohort followed from birth to age 33 years. Included were questions on physical and social characteristics of each parent and the grandparents, and birth details of parent and first child. In the present study, fetal growth in non-preterm babies, after adjustment for the known effects of smoking and sex of the child, is explained best by factors relating to the parent's own growth, primarily in utero, but also to adulthood. There are small additional effects of education or social class but not of parent's gestational age. Only 15% of the variability in the child's fetal growth can be explained by the mother's characteristics and approximately 7% by the father's. Parent's own fetal growth accounts for nearly half of the variability if unadjusted for other factors and nearly a third after adjustment for sex of child, smoking, parental height and weight, maternal age at menarche and paternal age at first birth. Parental fetal growth makes the greatest anthropometric contribution.

Survival in cerebral palsy: the role of severity and diagnostic labels

The aim of this study was to review survival and certified causes of death of 584 children on a population-based register of cerebral palsy (CP), and to assess the impact on these of an additional diagnostic label. The register, established in 1985, comprised children with CP born from 1980 to about 1987 who were resident at the time of notification in the south-east of England in a region with between 3 and 4 million population, defined by the boundaries of the regional health authority (North East Thames Regional Health Authority). The current report concerns deaths of residents born between 1980 and 1986, who had been registered but had later died, as well as of eligible children who had not been registered while alive but whose cause of death was CP. These were identified at the Office of Population Censuses and Surveys who also supplied copies of death certificates for this study. For children notified while alive, information about motor severity and other diagnostic labels was sought at entry to the register and again between 3.5 and 4 years and between 7 and 8 years. For this study, children known to have a postneonatal onset, a progressive or non-cerebral cause of motor signs, or minimal motor involvement were excluded. Thirty-nine of 584 children included in this study had died by the end of 1995. No deaths had occurred in children known to have less than four-limb involvement. Survival of the group known to have an additional diagnostic label was significantly lower (86.2%) than that of the group with no known label (96.3%; P=0.01), and remained lower, although not significantly, if only those with severe four-limb involvement were compared (75.3% versus 92.4%; P=0.2). The greater severity of limb involvement in those with an additional diagnosis may not account for this difference. Of the 37 children with death certificates available, CP was mentioned as a cause in only 24.

Is there evidence of clustering in Down syndrome?

BACKGROUND

Associations between environmental hazards and the occurrence of congenital anomalies may be detectable by seeking evidence of non-random occurrence of cases (clusters). There have been a number of anecdotal reports of occurrences of clusters of Down syndrome (DS).

METHODS

Data from a national register of cytogenetic diagnoses of Down syndrome births and legal terminations occurring between 1989 and 1995 were used to examine the possibility of clustering. Space-time clustering at Regional Health Authority (RHA) level was examined by comparing the expected monthly number of DS pregnancies given the maternal age distribution, with the observed numbers. Knox's method was used to determine if any clustering of RHA of unexpectedly high prevalence had occurred. Seasonality was also investigated by comparing monthly expected and observed numbers of DS pregnancies. Time clustering was examined by using the scan statistic to determine whether a statistically significant excess of pregnancies in any 3-month period occurred in any individual or adjacent groups of District Health Authority (DHA).

RESULTS

The numbers of DS pregnancies were no higher than expected (P < 0.05) in the same RHA over consecutive months. There was no evidence of any seasonality of DS pregnancies (P > 0.5). Only two individual DHA and three pairs of adjacent DHA had significantly high scan statistics (P < 0.03), but as over 400 statistical tests had been completed 12 clusters would be expected to have occurred due to chance alone.

CONCLUSION

There was no evidence of any space-time clustering in DS at DHA level.

Monitoring fetal and infant survival using regional birth notification data in north east London

OBJECTIVE

To demonstrate the use of aggregated, locally collected birth notification data to examine trends in birth-weight specific survival for singleton and multiple births.

DESIGN

Retrospective analysis of 171,527 notified births and subsequent infant survival data derived from computerised community child health records. Validation of data completeness and quality was undertaken by comparison with birth and death registration records for the same period.

SETTING

Notifications of births in 1989-1991 to residents of the North Thames (East) Region (formerly North East Thames Regional Health Authority).

OUTCOME MEASURES

Birthweight specific stillbirth, neonatal, and postneonatal death rates.

RESULTS

There was close correspondence between the notification and registration data. For 96% of the registered deaths a birth notification record was identified and for the majority of these the death was already known to the Community Child Health Computer. Completeness of birth-weight data, particularly at the lower end of the range, was substantially better in birth notification data. Comparison with the most recent published national data relating to birthweight specific survival of very low birthweight singleton and multiple births suggests that the downward trend of mortality is continuing, at least in this Region.

CONCLUSIONS

The use of routinely collected aggregated birth notification data provides a valuable adjunct to existing sources of information about perinatal and infant survival, as well as other information regarding process and outcome of maternity services. Such data are required for comparative audit and may be more complete than that obtained from registration or hospital generated data.

The impact of diagnostic labelling in population-based research into cerebral palsy

This study explores and quantifies the impact on the estimation of prevalence rates and aetiological hypotheses of inclusion and exclusion of different diagnostic labels and types of cerebral palsy (CP). The study was based on data from a CP register which had been established in the English North East Thames Regional Health Authority (NETRHA). As a deliberate policy, no definition of CP was given to notifiers and no inclusion or exclusion criteria were specified. Clinical information, including known malformations, genetic disorders, and features that made the diagnosis doubtful, was requested. Rates and relative risks for different inclusion and exclusion criteria were calculated. The crude rate of CP as defined above was 1.6/1000 (95%CI 1.5, 1.7). Exclusion of all cases with a known or potentially causal association reduced this rate to 1.2/1000 (95%CI 1.0, 1.3). Comparison with an intensively investigated sample from Germany and Sweden showed that more of the same causal associations (or diagnostic labels) were found, particularly where MRI studies had been carried out. Future comparative studies in CP will need to be very precise in specifying inclusions and exclusions and in estimating the effects they will have on monitoring trends over time and aetiological hypotheses.

Medical causes on stillbirth certificates in England and Wales: distribution and results of hierarchical classifications tested by the Office for National Statistics

OBJECTIVE

To produce a classification of stillbirths registered in England and Wales compatible with a previously described classification for neonatal deaths; to compare national data for intrapartum stillbirths with those for the remaining stillbirths; and to report on stillbirths with a gestational age of 24 to 27 completed weeks first made registrable on 1 October 1992.

DESIGN

Algorithms were developed and tested to derive hierarchical cause classifications making use of multiple causes mentioned on stillbirth certificates.

RESULTS

The additional information available since 1986 on cause and time of death of stillbirths, classified in a hierarchical fashion allows a more meaningful interpretation of the available information on the causes of stillbirth than was previously possible and does not perturb ongoing trends. Antepartum deaths without a classifiable cause contributed the majority: between 1992 and 1994 they accounted for 43% if mentions of asphyxial conditions are regarded as classifiable causes, and 82% if not considered as causal. Stillbirths described as occurring intrapartum are consistently of higher gestational age and birthweight than the remainder, lending validity to the time of death given.

CONCLUSIONS

The national use of a classification including reported time of death of the fetus and mentions of asphyxial conditions is justifiable, providing a distinction is made between associated mentions and causal conditions. Better and more complete clinical information on stillbirth certificates will contribute further to understanding of their causes.

The effects of own fetal growth on reported hypertension in parous women aged 33

BACKGROUND

Data from the study of the British 1958 birth cohort, National Child Development Study (NCDS), has allowed wider investigation of the relationship between retarded fetal growth and risk of adult hypertension.

METHODS

A history of self-reported hypertension was related to fetal growth in 3308 parous cohort members. Fetal growth, the measure used, is the difference in actual birthweight from that expected for the gestational age and subsequent adult height. The relationships were investigated both linearly and non-linearly adjusting for potential confounders.

RESULTS

After adjustment for confounding factors, including adult weight for height, retarded fetal growth was associated with reported hypertension particularly when not confined to pregnancy. The latter was also associated with accelerated fetal growth, moderate or severe hypertension in the mother when pregnant with the cohort member, being relatively taller than your mother, and lack of educational qualifications. Hypertension confined to pregnancy was more likely among women who were themselves firstborn or older at childbirth. Neither maternal smoking during cohort's gestation nor cohort member's gestational age had a significant effect. The results are consistent with previous reports that fetal growth effects are less marked if gestation is short.

CONCLUSIONS

The relationships between fetal growth and subsequent hypertension are extremely complex and variable, and need to be studied allowing for deviations from growth potential. Adult weight for height remains the strongest predictor of hypertension. The results suggest that losing weight is likely to have the same proportional benefit in women with and without a history of retarded fetal growth.

Reliability of statistics on Down's syndrome notifications

OBJECTIVES

To evaluate the completeness of notifications of Down's syndrome live births and terminations to the Office for National Statistics (ONS) using data from the National Down Syndrome Cytogenetic Register (NDSCR). To examine the agreement of observed birth prevalence of Down's syndrome with the expected birth prevalence derived from published maternal age specific rates.

METHODS

The number of live births (adjusted to allow for the estimated underascertainment) and the number of terminations due to fetal Down's syndrome from NDSCR were compared with those figures reported to the ONS. Subsequently, using the NDSCR figures, the live birth prevalence of Down's syndrome that would have occurred in the absence of antenatal diagnosis and selective termination was calculated in England and Wales in the years 1990-1993. These figures were compared with those derived by applying published age specific prevalences to the maternal age distribution in England and Wales.

RESULTS

It is estimated that only 48% and 46% respectively of Down's syndrome live births and terminations of pregnancy were notified to ONS between 1990 and 1993. The annual expected birth prevalences of Down's syndrome obtained by applying maternal age specific prevalences to the maternal age distribution were in close agreement with observed rates from NDSCR.

CONCLUSIONS

There is considerable underreporting of Down's syndrome births and terminations to ONS. The NDSCR data are more complete and therefore the effects of screening should be monitored using data from this source, or using estimates derived from the age specific rates of Down's syndrome.

Antecedent circumstances surrounding neural tube defect births in 1990-1991. The Steering Committee of the National Confidential Enquiry into Counselling for Genetic Disorders

OBJECTIVE

To investigate births with neural tube defects at a time when most districts were screening for the condition. The objective was to document the circumstances surrounding each affected birth and assess the care provided against given standards.

DESIGN

Retrospective review of antenatal casenotes by the obstetric team.

POPULATION

Three hundred and eight births in England and Wales in 1990 to 1991 were reported to the Office of Population Census Survey (OPCS) to involve neural tube defects. Sufficient information was available to identify both the woman and the obstetrician in 213 pregnancies. Details were obtained from a questionnaire completed by the obstetric team for 168 (79%). In 20/168 cases either the reported outcome was not a live birth/stillbirth or the pregnancy did not involve a neural tube defect: eight resulted in a 'normal' infant, eight were terminated and in four the abnormality was not a neural tube defect. Thus 148 eligible cases were available for analysis.

RESULTS

Of the 148 births, the anomaly was not detected prenatally or detected later than 25 weeks of gestation in 98 cases (66%), diagnosed in a multiple pregnancy in 24 (16%) and diagnosed prenatally but the woman chose to continue the pregnancy in 26 (18%). Of the 98 births not detected prenatally or detected late during pregnancy, the surrounding circumstances were that screening was declined in six cases (4%), screening was not offered due to late booking in 30 (20%), serum alpha-fetoprotein screening gave a false negative result in eight (5%), ultrasound screening gave a false negative result in 29 (20%), both screening methods gave false negative results in 17 (11%) and other reasons in eight (5%). The estimated sensitivity of ultrasound screening for anencephaly was 100%. For spina bifida the estimated sensitivity for singleton pregnancies is higher for serum alpha-fetoprotein screening, 84% to 92%, than ultrasound screening, 70% to 84%, for a range of assumptions regarding the degree of under-reporting to OPCS of live births and terminations.

CONCLUSIONS

Late booking precluded the offer of screening tests in a substantial proportion (22%) of cases. The presence of multiple fetuses including one or more with a neural tube defect was a serious additional complication in prenatal screening, diagnosis and counselling. Screening for neural tube defects was widespread in 1990 to 1991, although variations in the services provided were documented. Ultrasound scanning was a major component but was associated with a lower sensitivity than maternal serum alpha-fetoprotein screening for neural tube defects other than anencephaly.

Cerebral palsy: effects of twinning, birthweight, and gestational age

AIMS

To determine the effects of birthweight and gestational age on the risk of cerebral palsy for multiple and singleton births.

METHODS

Children on the North East Thames Regional Health Authority Interactive Child Health System, born between 1 January 1980 and 31 December 1986, and notified as having cerebral palsy, were included. Cases of postneonatal onset, of known progressive, or non-cerebral pathology and with only mild signs were excluded. Rates and relative risks were calculated using the most complete data, which related to 1985-86, and comprised 102,059 singletons and 2367 twins. Logistic regression was used to examine the associations between being a twin, gestational age, and birthweight.

RESULTS

The crude rate per 1000 survivors at 1 year of age was 1.0 in singletons and 7.4 in twins. The relative risk was greatest in twins weighing more than 2499 g (4.5). However, after adjusting for reduced birthweight of twins it was the relative risk of twins weighing less than 1400 g that was significantly increased. Logistic regression confirmed that lower fetal growth, lower gestational age, and being a twin are all independent risk factors for cerebral palsy.

CONCLUSION

The increased risk to twins of cerebral palsy is not entirely explained by their increased risk of prematurity and low birthweight.

Cytogenetic and epidemiological findings in Down syndrome, England and Wales 1989 to 1993. National Down Syndrome Cytogenetic Register and the Association of Clinical Cytogeneticists

Data from the National Down Syndrome Cytogenetic Register is used to describe the cytogenetics and epidemiology of registered cases. The register comprises notifications from cytogenetics laboratories in England and Wales. This report is of 5737 cases registered between 1989 and 1993: 2169 prenatal and 3436 postnatal diagnoses, and 132 spontaneous abortions. Eighty eight registrations were from multiple pregnancies. Ninety five percent had regular trisomy 21. In 4% there was a translocation, mostly Robertsonian t(14;21) or t(21;21). One percent were mosaics with one normal cell line. Mean maternal age was raised in free trisomy 21, but not in translocations. Where families had been investigated, about a third of translocations were inherited, six to seven times more often from the mother than the father. Associations between free trisomy 21 and structural chromosomal defects in the births were no more common than expected from newborn series. The overall sex ratio was raised (male to female: 1.23 to 1), and there was an excess of associated male sex chromosomal aneuploidy. However, in mosaics with one normal cell line the male to female ratio was 0.8 to 1, and in twins discordant for trisomy 21 there was also a female excess.

Early mortality and morbidity in children with Down's syndrome diagnosed in two regional health authorities in 1989

OBJECTIVES - To assess the risk of early mortality and the quality of health of a recent cohort of 5 year old children with Down's syndrome to provide current information on prognosis. SETTING - A follow up study in 1994 of all live births with a cytogenetic diagnosis of trisomy 21 or related karyotype born in 1989 and diagnosed in the South East Thames and Oxford Regional Health Authorities; these amounted to 100 children. RESULTS - Eighteen of the sample of 100 had died in the first three years, and seven were reported as adopted. Fifty six mothers were interviewed, including five of children who had died. High rates of associated congenital defects were reported. The most common were congenital heart defects, which were reported for 29 of the 69 children for whom health information was available, and were certified as the underlying cause of death of 12 and required surgery in 11. At least five children had had gastrointestinal atresia or other gut blockage, most presenting at birth but one case occurring at 3 years, and these had necessitated a colostomy in two cases. Leukaemia had occurred in two children, both of whom had died. As expected mothers also reported high rates of defects of hearing, often treated with grommets; of vision; and frequent severe infections. CONCLUSIONS - Information of this nature, as well as that regarding the more positive aspects of Down's syndrome, should be made available to those counselling parents considering the offer of diagnostic tests.

A twin study of congenital hemiplegia

Twins were more than three times more common in a large sample of London children with congenital hemiplegia than in the general population. This over-representation of twins could largely be explained by their higher rate of preterm birth, though twin-specific risk factors, including the consequences of a co-twin's death in utero, may also have played a part. None of the 34 co-twins who survived infancy had hemiplegia or any other form of cerebral palsy. Among 155 siblings of singletons with congenital hemiplegia, no child had hemiplegia and only one had cerebral palsy. Perhaps it is chance rather then genetic liability or an adverse environment that primarily governs who does and does not become congenitally hemiplegic.