Live Birth Prevalence Of Down Syndrome Research Articles

Non-invasive prenatal testing for everybody or contingent screening?

To compare the advantages and disadvantages of two main implementation strategies for non-invasive prenatal testing (NIPT) for the detection of trisomies 21, 13 and 18 in public healthcare settings. These concern NIPT as a first-tier screening test for all pregnant women, or NIPT contingent on an increased risk first-trimester combined test (FCT) result. Comparison based on (un)published data and literature. Despite the lower prevalence of trisomies in the low-risk population, data show that the positive predictive value (PPV) and detection-miscarriage ratio of first-tier NIPT are comparable to NIPT used as contingency test. Advantages of NIPT as a first-tier test compared to FCT with contingent NIPT are that there is no time-window for testing, sensitivity is higher, fewer women need follow-up testing (PPV of NIPT is higher than PPV of FCT), less anxiety for pregnant women and partners. When given the choice, pregnant women prefer first-tier NIPT. Although contingency testing still seems to be the cheaper option, the differences in costs are becoming increasingly smaller and might soon disappear. We argue that NIPT should preferably be offered as a first-tier test for the detection of fetal aneuploidies for all pregnant women, provided that women are supported to make informed decisions. This article is protected by copyright. All rights reserved.

Neonatal mortality and morbidity in Down syndrome in the time of prenatal aneuploidy testing: a retrospective cohort study

The total uptake of prenatal aneuploidy screening for Down syndrome (DS) is increasing worldwide. As a result of increasing prenatal diagnosis of DS and subsequent termination of pregnancy, livebirth prevalence of DS is decreasing. The aim of this study is to explore the impact of an increasing uptake of prenatal aneuploidy screening on the neonatal mortality and morbidity in DS. This is a retrospective cohort study of 253 neonates with DS born between 2012 and 2018 that were seen at the outpatient clinic of five hospitals in the Netherlands. The medical files were reviewed for maternal and neonatal characteristics and neonatal morbidities. The Dutch national birth registry (Perined) provided mortality numbers of neonates with DS. The results were interpreted in the context of other published studies. Neonatal mortality in DS remained stable, ranging from 1.4 to 3.6%. A congenital heart defect (CHD) was found in 138 of the 251 neonates (55.0%) with atrial septal defect, atrioventricular septal defect, and ventricular septal defect being the most common. The type of CHD in DS did not change over time. Gastro-intestinal defects were present in 22 of the 252 neonates with DS (8.7%), with duodenal atresia as the most reported anomaly. Persistent pulmonary hypertension of the neonate (PPHN) was found in 31 of the 251 infants (12.4%). Conclusions: Although uptake of prenatal aneuploidy screening increased, neonatal mortality and morbidity in DS appears to be stable. An increased incidence of PPHN was found.What is Known:• The total uptake of prenatal aneuploidy screening for Down syndrome is increasing worldwide.• As a result of increasing prenatal diagnosis of Down syndrome and subsequent termination of pregnancy, the livebirth prevalence of Down syndrome is decreasing.What is New:• Although uptake of prenatal aneuploidy screening increased, neonatal mortality and morbidity in Down syndrome appears to be stable.• An increased incidence of persistent pulmonary hypertension of the neonate was found.

Does non-invasive prenatal testing affect the livebirth prevalence of Down syndrome in the Netherlands? A population-based register study.

ObjectiveTo evaluate if non‐invasive prenatal testing (NIPT) affects livebirth (LB) prevalence of Down syndrome (DS) in the Netherlands.MethodData from clinical genetics laboratories and the Working Party on Prenatal Diagnosis and Therapy (2014–2018) and previous published data (1991–2013) were used to assess trends for DS LB prevalence and reduction percentage (the net decrease in DS LBs resulting from selective termination of pregnancies). Statistics Netherlands provided general population data.ResultsDS LB prevalence increased from 11.6/10,000 in 1991 to 15.9/10,000 in 2002 (regression coefficient 0.246 [95% CI: 0.105–0.388; p = 0.003]). After 2002, LB prevalence decreased to 11.3/10,000 in 2014 and further to 9.9/10,000 in 2018 (regression coefficient 0.234 (95% CI: −0.338 to −0.131; p < 0.001). The reduction percentage increased from 26% in 1991 to 55.2% in 2018 (regression coefficient 0.012 (95% CI: 0.010–0.013; p < 0.001)). There were no trend changes after introducing NIPT as second‐tier (2014) and first‐tier test (2017).ConclusionsIntroducing NIPT did not change the decreasing trend in DS LB prevalence and increasing trend in reduction percentage. These trends may be caused by a broader development of more prenatal testing that had already started before introducing NIPT.

Estimates of live birth prevalence of children with Down syndrome in the period 1991-2015 in the Netherlands.

In Western countries, increasing maternal age has led to more pregnancies with a child with Down syndrome (DS). However, prenatal screening programs, diagnostic testing and termination of pregnancy influence the actual DS live birth (LB) prevalence as well. The aim of this study is to examine these factors in the Netherlands for the period 1991-2015. In our study, we establish a baseline for DS LB prevalence before non-invasive prenatal testing will be made available to all pregnant women in the Netherlands in 2017. Full nationwide data from the Dutch cytogenetic laboratories were used to evaluate the actual DS LB prevalence. In addition, nonselective DS prevalence, which is the DS LB prevalence that would be expected in absence of termination of pregnancies, was estimated on the basis of maternal age distribution in the general population. Because of an increase in maternal age, nonselective DS prevalence increased from around 15.6 [95% confidence interval (CI) 13.9-17.4] per 10000 LBs in 1991 (311 children in total) to around 22.6 (95% CI 20.3-24.9) per 10000 in 2015 (385), the increase levelling off in recent years. Actual LB prevalence rose from around 11.6 (95% CI 10.9-12.2) per 10000 in 1991 (230 children) to an estimated peak of 15.9 (95% CI 15.6-16.2) per 10000 in 2002 (322), gradually decreasing since to 11.1 (95% CI 10.8-11.5) per 10000 in 2015 (190). Reduction of DS LBs resulting from elective terminations had been fairly constant between 1995 and 2002 at around 28% and rose afterwards from 35% in 2003 to around 50% in 2015. In spite of expansion of antenatal screening in the Netherlands in the 1990s and early 2000s, actual DS LB prevalence increased during this period. However, after 2002, this trend reversed, probably because of informing all pregnant women about prenatal testing since 2004 and the implementation of a national screening program in 2007.

Associated congenital anomalies among cases with Down syndrome

Down syndrome (DS) is the most common congenital anomaly widely studied for at least 150 years. However, the type and the frequency of congenital anomalies associated with DS are still controversial. Despite prenatal diagnosis and elective termination of pregnancy for fetal anomalies, in Europe, from 2008 to 2012 the live birth prevalence of DS per 10,000 was 10. 2. The objectives of this study were to examine the major congenital anomalies occurring in infants and fetuses with Down syndrome. The material for this study came from 402,532 consecutive pregnancies of known outcome registered by our registry of congenital anomalies between 1979 and 2008. Four hundred sixty seven (64%) out of the 728 cases with DS registered had at least one major associated congenital anomaly. The most common associated anomalies were cardiac anomalies, 323 cases (44%), followed by digestive system anomalies, 42 cases (6%), musculoskeletal system anomalies, 35 cases (5%), urinary system anomalies, 28 cases (4%), respiratory system anomalies, 13 cases (2%), and other system anomalies, 26 cases (3.6%). Among the cases with DS with congenital heart defects, the most common cardiac anomaly was atrioventricular septal defect (30%) followed by atrial septum defect (25%), ventricular septal defect (22%), patent ductus arteriosus (5%), coarctation of aorta (5%), and tetralogy of Fallot (3%). Among the cases with DS with a digestive system anomaly recorded, duodenal atresia (67%), Hirschsprung disease (14%), and tracheo-esophageal atresia (10%) were the most common. Fourteen (2%) of the cases with DS had an obstructive anomaly of the renal pelvis, including hydronephrosis. The other most common anomalies associated with cases with DS were syndactyly, club foot, polydactyly, limb reduction, cataract, hydrocephaly, cleft palate, hypospadias and diaphragmatic hernia. Many studies to assess the anomalies associated with DS have reported various results. There is no agreement in the literature as to which associated anomalies are most common in cases with DS with associated anomalies. In this study we observed a higher percentage of associated anomalies than in the other reported series as well as an increase in the incidence of duodenal atresia, urinary system anomalies, musculoskeletal system anomalies, and respiratory system anomalies, and a decrease in the incidence of anal atresia, annular pancreas, and limb reduction defects. In conclusion, we observed a high prevalence of total congenital anomalies and specific patterns of malformations associated with Down syndrome which emphasizes the need to evaluate carefully all cases with Down syndrome for possible associated major congenital anomalies.

Contingent non-invasive prenatal testing: an opportunity to improve non-genetic aspects of fetal aneuploidy screening.

Several countries today struggle with suboptimal performances in many aspects of the fetal aneuploidy screening process and consider introducing non-invasive prenatal screening (NIPT) as a solution. In this study, costs and benefits of different scenarios for contingent NIPT screening in Belgium are evaluated with respect to partial redistribution of the national screening budget into quality improving measures for those screening activities that will be maintained when full NIPT screening is implemented. Data from the Belgian National Institute for Health and Disability Insurance and the Study Centre for Perinatal Epidemiology were used in modeled calculations of medical and economic impact of NIPT after prior conventional screening (1) at thresholds 1:300 and 1:600, and (2) at current and improved screening sensitivity. Contingent NIPT screening under current screening conditions would maintain today's 7.9(0)/000 live birth prevalence of Down syndrome (LBPD) at an 11% reduction of overall short-term costs. Lowering the screening threshold to 1:600 or increasing sensitivity by 10% would reduce LBPD to 7(0)/000 at a maximum 3% increase of overall short-term costs. Today, in Belgium and in many other countries, full NIPT screening is considered too expensive for immediate introduction into the national fetal aneuploidy screening program. Contingent NIPT screening is both clinically and economically beneficial. A temporary contingent NIPT protocol allows for reinvesting economic savings into optimization of those screening aspects, which are to be maintained in parallel to full NIPT screening.

Estimates of the live births, natural losses, and elective terminations with Down syndrome in the United States

The present and future live birth prevalence of Down syndrome (DS) is of practical importance for planning services and prioritizing research to support people living with the condition. Live birth prevalence is influenced by changes in prenatal screening technologies and policies. To predict the future impact of these changes, a model for estimating the live births of people with DS is required. In this study, we combine diverse and robust datasets with validated estimation techniques to describe the non-selective and live birth prevalence of DS in the United States from 1900-2010. Additionally, for the period 1974-2010, we estimate the impact of DS-related elective pregnancy terminations (following a prenatal diagnosis of DS) on the live births with DS. The live birth prevalence for DS in the most recent years (2006-2010) was estimated at 12.6 per 10,000 (95% CI 12.4-12.8), with around 5,300 births annually. During this period, an estimated 3,100 DS-related elective pregnancy terminations were performed in the U.S. annually. As of 2007, the estimated rates at which live births with DS were reduced as a consequence of DS-related elective pregnancy terminations were 30% (95% CI: 27.3-31.9) for the U.S. as a whole. Our results and our model provide data on the impact of elective pregnancy terminations on live births with DS and may provide a baseline from which future trends for live births with DS can be estimated.

The importance of rapid aneuploidy screening and prenatal diagnosis in the detection of numerical chromosomal abnormalities

ObjectivesEvaluation of Fluorescent in situ hybridization (FISH) as a tool for rapid aneuploidy screening (RAS) of high risk pregnancies, before its approval in the national antenatal screening and genetic diagnosis program in Egypt.MethodsThe cytogenetic data of prenatal specimens, and results of FISH of 100 patients performed between, January 2009 and December 2009, at the Medical Genetics Center (MGC) laboratory were retrieved and reviewed. AneuVysion Assay kit was used for detection of 13, 21, X, Y, 18 aneuploidies.ResultsMaternal age varied from 21 to 44 years (mean was 35.6 year). Ninety percent of pregnancies had normal chromosomes and 10% of the cases had numerical chromosomal abnormalities. Trisomy 21 was the most frequent chromosomal disorder across all indications (5%), followed by Turner syndrome (2%), trisomy 18 (2%), and trisomy 13 (1%). When comparing the FISH data with karyotype results for chromosomes 13, 18, 21, X, and Y in the 83 individual tested, no false positive or negative results were detected by the FISH assay. The result obtained by FISH and the banding cytogenetic were in complete accordance.ConclusionThis study supports the integration of amniotic fluid (AF) FISH as a RAS test, in to routine antenatal practice for identification of chromosome aneuploidies. There are trends towards delayed childbearing and most cases of Down Syndrome (DS) are currently detected post-nataly in the Egyptian population. Consequently, the live birth prevalence of DS has increased, which might lead to a serious negative public health effects.

Total &amp; Livebirth Prevalence of Down Syndrome and Other Trisomies in Europe 1990-2007: Impact of Increasing Maternal Age, Prenatal Screening and Termination of Pregnancy

Background and aims: This study aims to examine trends in total and livebirth (LB) prevalence of trisomies 21, 18 and 13 (T21, T18, T13) with regard to increasing maternal age and prenatal diagnosis in Europe; and to examine geographical variation in LB prevalence of T21.Methods: The study population consisted of 21 registries in 12 European countries covering 5.1 million births, 1990-2007. Over 15,000 cases of trisomy including LB, fetal deaths (FD) from 20 weeks gestational age )GA(, and terminations of pregnancy for fetal anomaly (TOPFA) were extracted from EUROCAT database. Poisson regression was used to assess trends over time and to examine the effect of maternal age and correction for survival to 20 weeks GA.Results: The proportion of births born to mothers aged 35+ increased from 13% in 1990 to 20% in 2007. Total prevalence per 10,000 births was 21.6 for T21, 4.8 for T18 and 2.0 for T13; LB prevalence was 11.1 for T21, 1.0 for T18 and 0.5 for T13. There was a significantly increasing trend over time in total prevalence of the 3 trisomies, while LB prevalence remained stable. Maternal age significantly contributed to these trends while correcting for survival had little effect. There was three-fold geographical variation in LB prevalence of T21 between countries.Conclusion: The rise in older mothers has led to an increase in the number of trisomy-affected pregnancies in Europe. Prenatal screening and TOPFA have counteracted the effect of increasing maternal age on LB prevalence in most countries.

Live birth prevalence of Down syndrome in Tottori, Japan, 1980–1999

One hundred sixty-four patients with Down syndrome (DS) were confirmed in Tottori Prefecture, Japan, from 1980 to 1999. The sex ratio of 1.52 (99 males and 65 females) was comparable to that reported in previous studies. The live birth prevalence per 1,000 was 1.52 (95% CI: 1.29-1.75) from 1980 to 1999, with a prevalence of 1.34 (95% CI: 1.05-1.63) recorded between 1980 and 1989, and 1.74 (95% CI: 1.37-2.11) between 1990 and 1999. There was no statistically significant change between these two decades (chi(2)-test). Live birth prevalence in these two decades showed a significant increase (chi(2)-test, P < 0.005) compared with that recorded in 1969-1978 in Tottori Prefecture (0.803, 95% CI: 0.677-0.929). Mean ages of mothers at the birth of a DS patient were 31.0 years in 1980-1989 and 32.4 years in 1990-1999 (t-test, no significant difference). Dispersion analysis on the mean age of mothers at birth for patients born between 1969-1978, 1980-1989, and 1990-1999 showed a significant difference (t-test, P < 0.005), while comparing the mean age of mothers in 1969-1978 to those in 1990-1999 also revealed a significant difference (t-test, P < 0.001). Live birth prevalence has increased due to the rise in fertility rates among older women, although maternal age-specific risk rates remain unchanged. The widespread introduction of induced abortion following prenatal diagnosis decreased live birth prevalence of DS largely in European (and a few Asian) countries after 1990, or kept prevalence steady, despite increasing fertility rates among women aged 30 and over. In contrast, all published studies have reported an increase in live birth prevalence of this syndrome in Japan, probably resulting from the fact that prenatal diagnoses are used only exceptionally in this country (due to the negative attitude toward selection of life in Japanese culture).

The Prevalence of Live Birth Down Syndrome in the Region of Primorsko-goranska County in Croatia, 1996–2005: The Impact of Screening and Amniocentesis

To investigate the prevalence of live birth Down syndrome (DS) in the region of Primorsko-goranska County (PGC) in Croatia from 1996 to 2005 and to evaluate the impact of second-trimester maternal serum screening (MSS) and amniocentesis on live birth DS prevalence. Study was based on databases from the Department of Gynecology and Obstetrics, University Hospital Centre Rijeka, the Department of Biology and Medical Genetics, School of Medicine, University of Rijeka, and the Croatian National Institute of Public Health. The regional policy of prenatal diagnosis for DS includes amniocentesis for pregnant women aged 35 or over and MSS for younger women. We estimated live birth and total prevalence of DS and measured the proportion of pregnant women using MSS and amniocentesis. Trends of live birth and total prevalence of DS were tested by linear regression analysis. The live birth prevalence of DS was 1.4/1000 in the period 1996-2005. A decreasing, but nonsignificant, trend of prevalence was observed over time (P = 0.577). Women aged 35 or over represented 11.6% of all pregnant women included in the study. The proportion of women who had MSS was 33.9%. The proportion who underwent amniocentesis was 6.1%. No marked decrease in prevalence of live birth DS was observed in the region of PGC during the last 10 years. The usage of MSS and amniocentesis was too low to have any significant impact on live birth DS prevalence. Women's, as well as physician's, knowledge and attitudes towards prenatal diagnosis of DS should be evaluated.

Advances in Medical Technology and Creation of Disparities: The Case of Down Syndrome

We assessed socioeconomic differences in probabilities of prenatal diagnoses of Down syndrome and continuation of pregnancies after such diagnoses, along with the effects of these differences on disparities in live-birth prevalences of Down syndrome. Using population-based data derived from 1433 cases of Down syndrome and 3731 control births, we assessed age-adjusted effects of maternal occupation and geographic origin on prenatal diagnoses, as well as overall and live-birth odds, of Down syndrome. Maternal occupation and geographic origin had significant effects on the probability of a prenatal diagnosis of Down syndrome and on continuation of pregnancy after such a diagnosis. Women in lower-status occupational categories had higher odds of delivering a live-born infant with Down syndrome. In comparison with women in the highest-status occupational category, the age-adjusted odds ratio for a Down syndrome live birth among women without an occupation was 2.4 (95% confidence interval [CI] = 1.7, 3.3). By contrast, there were no disparities in age-adjusted overall likelihood of Down syndrome. Socioeconomic differences in use of prenatal testing have created disparities in the live-birth prevalence of Down syndrome. Overall Down syndrome risk does not vary according to socioeconomic status.

Maternal age‐specific fetal loss rates in Down syndrome pregnancies

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. 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. 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. 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.

Patient choice and the randomized controlled trial

Patient choice and the randomized controlled trial

La mesure de la clarté nucale et le dosage des marqueurs sériques commencent-ils à modifier l'incidence de la trisomie 21 en France ?

Objective. – To evaluate the impact of prenatal screening for Down Syndrome in France in relation to the important changes in the French prenatal screening policy during the years 1996–1997: measurement of nuchal translucency and maternal serum screening, for all women. Patients and method. – Data are those published from three congenital anomalies registries implanted in Centre-Est, Paris and Bas-Rhin areas, from 1990 to 2001. Results. – The livebirth prevalence of Down Syndrome decreased from 1/950 in 1990 to 1/1500 in 2000–2001. This decrease was observed from 1994 onwards but has proved stronger since 1996, in spite of the observed increase in the total prevalence partly explained by changes in the maternal age distribution. Extrapolated to all births in France, the calculated annual number of Down Syndrome births would decrease from 800–900 in 1990 to 500–600 in 2001. Consequently, the proportion of induced terminations following prenatal diagnosis increased from 38.6% in 1990 to 75.5% in 2001. In addition, the mean gestational age of the induced terminations is decreasing. Conclusion. – It seems reasonable to assume that the observed trends followed the changes in the French national policy for prenatal screening: a mass screening for all women, whatever the maternal age.

Trends in live birth prevalence of down syndrome in the Northern Netherlands 1987-96: the impact of screening and prenatal diagnosis.

In the Northern Netherlands, we examined the live birth prevalence of Down syndrome (DS) and the impact of maternal serum screening (MSS) and prenatal cytogenetic diagnosis (PCD) during the period 1987-96. In this period the live birth prevalence, based on the maternal age distribution and the age specific risk of delivering a child with DS was expected to increase from 1.26 in 1987 to 1.62 in 1996. The introduction of MSS in 1991 made PCD available to women of all ages. Nevertheless, the utilization of PCD remained very stable. In 1991, 4.7% of pregnant women underwent a diagnostic test. In 1996 this percentage was 6.4%. As a result of MSS and PCD, the live birth prevalence of DS was 19% lower than expected (p<0.01). Despite utilization of PCD based on opting-in and a discouraging government policy regarding the offer of MSS, the percentage of DS cases detected by PCD increased from of 17% during the period 1987-90 to 27% in the period 1991-96 when MSS was available. The percentages have been corrected for spontaneous pregnancy loss. From a medical and financial point of view, MSS was the most cost-effective indication for PCD. However, the potential of reducing the birth prevalence of DS is limited by the low utilization of MSS and PCD by pregnant women.

International variation in reported livebirth prevalence rates of Down syndrome, adjusted for maternal age

Reported livebirth prevalence of Down syndrome (DS) may be affected by the maternal age distribution of the population, completeness of ascertainment, accuracy of diagnosis, extent of selective prenatal termination of...

Application of Markov Chain Monte Carlo Methods to Modelling Birth Prevalence of Down Syndrome

SUMMARY Data collected before the routine application of prenatal screening are of unique value in estimating the natural live-birth prevalence of Down syndrome. However, much of these data are from births from over 20 years ago and they are of uncertain quality. In particular, they are subject to varying degrees of underascertainment. Published approaches have used ad hoc corrections to deal with this problem or have been restricted to data sets in which ascertainment is assumed to be complete. In this paper we adopt a Bayesian approach to modelling ascertainment and live-birth prevalence. We consider three prior specifications concerning ascertainment and compare predicted maternal-age-specific prevalence under these three different prior specifications. The computations are carried out by using Markov chain Monte Carlo methods in which model parameters and missing data are sampled.

Impact of prenatal diagnosis on revised livebirth prevalence estimates of Down syndrome in the Lothian region of Scotland, 1978–1992

Ramsay et al. [(1991) Biomed Pharmacother 45:267–272] reported on the livebirth prevalence of Down syndrome in the Lothian region of Scotland during 1978–1989. Their results suggested a temporal association between the events of Chernobyl in April 1986 and a significant excess of cases in 1987. In the current study the data were extended for 3 years and reanalyzed, a major objective being to correct for the differential loss of fetuses with Down syndrome which occurs between prenatal diagnosis and birth. Other objectives were to estimate the prevalence reduction due to prenatal diagnosis, quinquennial maternal age-specific risk rates, and the level of ascertainment of cases. The reanalysis found a 12-year prevalence rate of 1.29 vs. the previous rate of 1.34, and a shift of the annual prevalence peak to 1988, with a reduced prevalence in 1987 compared to that found in the earlier study. The new results are less consistent in showing an association of Down syndrome clustering with the Chernobyl accident. For the 15-year study period, a 23% overall reduction in prevalence occurred due to prenatal diagnosis and elective abortion of affected fetuses, with a 50% reduction to women ≥35 years of age. For 1988–1992, these reductions were 33% and 60%, which are among the highest reported in the literature for these time periods. The estimated quinquennial maternal risk rates were very similar to others already reported, and the data are consistent with a high level of case ascertainment. Since these women are approaching the upper limits of fetal detection through advanced maternal age alone, continued reduction in prevalence rates for Down syndrome through prenatal diagnosis and elective abortion will come mostly from increased use of other (chemical) screening techniques now available. © 1996 Wiley-Liss, Inc.

The effects of prenatal diagnosis, population ageing, and changing fertility rates on the live birth prevalence of Down syndrome in New York State, 1983-1992.

The incidence of Down syndrome (DS) at conception is highly dependent on the maternal age distribution and age-specific pregnancy rates. The live birth prevalence of DS reflects these factors and fetal deaths. This study examined DS live birth prevalence from 1983 to 1992 in New York State and analysed the effects of demographic changes and prenatal diagnosis use on the observed live birth prevalence. Expected DS live birth prevalence without prenatal diagnosis was calculated and compared with observed. Data were obtained from birth defects registries, vital records, and population data maintained by the New York State Department of Health. Over time, DS live birth prevalence was stable at about 10.4 per 10,000 live births. The percentage and number of women in the population above age 30 increased, as did birth rates among these women. Birth rates among younger women decreased. The proportion of DS babies born to women aged 35 and over increased from 27.1 to 34.1 per cent. Use of prenatal diagnosis by this age group ranged from 39.6 to 43.2 per cent, and increased steadily from 1.8 to 4.3 per cent among women under 35. Detection of DS fetuses increased from 82 in 1985 to 233 in 1992. Without prenatal diagnosis, DS live birth prevalence in 1992 would have reached 15.3 per 10,000 live births compared to the 10.2 observed. Prenatal diagnosis has prevented an increase in DS live birth prevalence but has not been sufficient to reduce live birth prevalence significantly.