The evolving national birth prevalence of Down syndrome in Taiwan. A study on the impact of second-trimester maternal serum screening

Understanding the genetic mechanisms and cognitive impairments in Down syndrome: towards a holistic approach

The most common genetic cause of intellectual disability is Down syndrome (DS), trisomy 21. It commonly results from three copies of human chromosome 21 (HC21). There are no mutations or deletions involved in DS. Instead, the phenotype is caused by altered transcription of the genes on HC21. These transcriptional variations are responsible for a myriad of symptoms affecting every organ system. A very debilitating aspect of DS is intellectual disability (ID). Although tremendous advances have been made to try and understand the underlying mechanisms of ID, there is a lack of a unified, holistic view to defining the cause and managing the cognitive impairments. In this literature review, we discuss the mechanisms of neuronal over-inhibition, abnormal morphology, and other genetic factors in contributing to the development of ID in DS patients and to gain a holistic understanding of ID in DS patients. We also highlight potential therapeutic approaches to improve the quality of life of DS patients.

The impact of prenatal screening tests on prenatal diagnosis in Taiwan from 2006 to 2019: a regional cohort study

BACKGROUND

The purpose of this study is to evaluate the impact of prenatal screening tests on prenatal diagnosis in Taiwan's 14 years from 2006 to 2019.

METHODS

The prenatal screening methods evolved from the second-trimester serum screening to combined first-trimester screening (cFTS) and then followed by the non-invasive cell-free DNA prenatal test (NIPT). The data used by the Department of Statistics, the Ministry of Health and Welfare and Department of Household Registration, Ministry of the Interior public website.

RESULTS

This regional registry-based cohort retrospective study examined a total of 2,775,792 births from January 2006 to December 2019. The proportion of advanced maternal age (AMA) pregnancies increased from 11.63% in 2006 to 30.94% in 2019. Overall, invasive diagnostic testing was used in 87.22% of AMA pregnancies. The prenatal detection rate of trisomy 21 and 18 increased from 74.1% and 83.3% in 2006 to 96.9% and 98.8% in 2019, respectively.

CONCLUSION

During the second-trimester and cFTS periods, the percentage of AMA pregnancies increased every year and the number of invasive procedures also accompany with increased percentage of AMA. However, during the period that NIPT were implemented, the percentage of invasive procedures decreased.

Demographic Assessment of Down Syndrome: A Systematic Review

The objective of this study is to assess the evidence about the demographic transformation of the Down Syndrome population, with a specific focus on prenatal testing, and to identify sources frequently used for demographic assessment of Down Syndrome in the world. We reviewed existing studies on demographic transformations in the population with Down Syndrome, specifically birthrate indicators, under the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement. The searches were made in Medline (via EBSCO Host), Academic Search Complete (via EBSCO Host), PsycINFO (via EBSCO Host), Web of Science (Core Collection), Public Health Database (via ProQuest), and The Cochrane Library. The terms were developed through Medical Subject Headings (MESH) and American Psycological Asociation Thesaurus of Psychological Index Terms (APA). Full texts were reviewed if information was given regarding location and birthrate for a range of three years or more, and if the first and last year considered was within 1960 and 2019. We found 22 references with a period of study between 1960 and 2019 following the global spread of prenatal testing for Down Syndrome. We found a consistent association between prenatal diagnosis and birthrate, enough to explain the significant fall in the prevalence of Down Syndrome, a somewhat rising incidence of Down Syndrome related to increased maternal age and extension of fertility services in healthcare systems, a generalized use of specific congenital birth defect registries as the primary source of data, and an unclear influence of socio-cultural and territorial variables. Our findings can inform research, policy, and practice to improve the reproductive health and quality of life of the population with Down Syndrome.

Has noninvasive prenatal testing impacted termination of pregnancy and live birth rates of infants with Down syndrome?

BACKGROUND

Implementation of noninvasive prenatal testing (NIPT) as a highly accurate aneuploidy screening test has raised questions around whether the high uptake may result in more terminations of pregnancies and fewer births of children with Down syndrome (DS).

AIM

The aim of the study was to investigate the impact of NIPT on termination and live birth rates for DS.

METHODS

Literature reporting pregnancy outcomes following NIPT was reviewed. Termination rates were calculated for women with a high-risk NIPT result for DS. Two audits of pregnancy outcomes where NIPT indicated DS were conducted in the United Kingdom and Singapore.

RESULTS

Fourteen studies from the United States, Asia, Europe, and the United Kingdom were included in the review. Live births of children with DS were reported in 8 studies. Termination rates following NIPT were unchanged or decreased when compared to termination rates prior to the introduction of NIPT. Audits found 15 of 43 women in the United Kingdom and 2 of 6 in Singapore continued pregnancies following a high-risk NIPT result.

CONCLUSIONS

Termination rates following the detection of DS by NIPT are unchanged or decreased compared to historical termination rates. Impact on live birth rates may be minimal in settings where termination rates fall. Population-based studies are required to determine the true impact.

Down Syndrome Screening in India: Are We There Yet?

Down syndrome is the most common cause of intellectual disability among live born children and is amenable to prenatal detection. Screening for Down syndrome on a population basis requires a thorough understanding of the principles involved in the screening tests. We discuss the rationale behind the commonly available screening tests and the Indian scenario in this setting.

A population-based study of prevalence of Down syndrome in Southern Thailand

BACKGROUND

Down syndrome (DS) is the most common chromosomal disorder that causes mental retardation. In 2009, a population-based birth defects study was implemented in three provinces in southern Thailand. This study aimed to determine the prevalence of DS in the studied regions, and the proportion of DS fetuses detected by prenatal screening.

METHODS

Data were obtained from a population-based surveillance study undertaken during 2009-2013. Entries in the birth defects registry included live births, stillbirths after 24 weeks gestational age, and terminations of pregnancy following prenatal diagnosis. Infants with clinical characteristics of DS had a chromosomal study to make a definite diagnosis.

RESULTS

Of the total 186 393 births recorded during the study period, 226 DS cases were listed, giving a prevalence of 1.21 per 1000 births [95% confidence interval (CI) 1.05-1.37]. The median maternal age was 36.5 years with a percentage of maternal age ≥35 years of 60.6%. Seventy-seven cases (34.1% of all cases) were diagnosed prenatally and these pregnancies were terminated. The prevalence of DS per 1000 births was significantly higher in older women, from 0.47 (95% CI 0.28-0.67) in mothers aged <30 years to 0.88 (95% CI 0.59-1.17) in mothers 30-<35 years (P<0.01), and to 4.74 (95% CI 3.95-5.53) in mothers ≥35 years (P<0.001).

CONCLUSIONS

The prevalence of DS significantly increased with maternal age. About 35% of DS cases were detected prenatally and later terminated. Hence, examining only registry live births will result in an inaccurate prevalence rate of DS.

Prenatal cytogenetic diagnosis in Taiwan: a nationwide population-based study

PURPOSE

The goal of this study was to gain a better understanding of the status of advanced maternal age among criteria for provision of amniocentesis in pregnant women in Taiwan.

MATERIALS AND METHOD

Data of 315 670 second-trimester amniocenteses from 28 national certified cytogenetics laboratories were retrospectively analyzed from the Prenatal Genetic Diagnosis Declaring and Database System of the Health Promotion Administration, Ministry of Health and Welfare in Taiwan between 2006 and 2013.

RESULTS

The number of pregnant women undergoing amniocentesis in Taiwan between 2006 and 2013 increased, and the most common three indications for amniocentesis were advance maternal age (75.11%), abnormal second trimester maternal serum screening (13.22%) and abnormal sonographic finding (8.00%). Down syndrome was the most common autosomal abnormality identified (25.74%); Turner syndrome was the most common sex chromosome abnormality (7.04%). Of structural rearrangements, 26.93% were balanced translocations and 17.10% were unbalanced translocations. The greatest proportion of fetal chromosomal abnormalities was found in cases where parents were also affected (38.02%).

CONCLUSIONS

Clinical workers should provide detailed genetic diagnostic information to pregnant women, especially those with the common amniocentesis indications, which will enable them to determine a birth plan.

Functional independence of Taiwanese children with Down syndrome

AIM

Information regarding the functional strengths and weaknesses of children with Down syndrome is important for early intervention programmes and for agencies providing family support and educational services.

METHOD

This study used the Functional Independence Measure for Children (WeeFIM) questionnaire for the parents or caregivers of 166 Taiwanese children (101 males and 65 females; median age 12y 7mo; range 3y 2mo-19y 1mo) with Down syndrome to assess their functional skills.

RESULTS

Out of a potential score of 126, the mean total WeeFIM score was 101.2. There was no statistically significant difference between the scores from the male and female participants (100.4 [SD 21.4] vs 102.4 [SD 24.7]; p>0.05). The mean scores for three domains (self-care, mobility, and cognition) were 45, 33, and 23 respectively (maximum of 56, 35, and 35 respectively). Performance was strongest in the mobility domain and weakest in the cognition domain. The total WeeFIM scores and 18 subscores for the three domains all positively correlated with age (p<0.05).

INTERPRETATION

For children with Down syndrome, some support and supervision is required for cognition and self-care tasks. The WeeFIM questionnaire may be useful for identifying the strengths and limitations of children with developmental disabilities and their families.

Integrated care for Down syndrome

Down syndrome (DS), caused by an extra copy of chromosome 21 (trisomy 21), is the most intensively studied human aneuploidy condition. It is the leading cause of intellectual disability and birth defects. Although most prenatally diagnosed DS fetuses are aborted in Taiwan, there are still some infants with DS who are diagnosed after birth. In addition to intellectual disability, people with DS face systemic problems that include short stature, dysmorphism, congenital heart disease, congenital anomalies of gastrointestinal and genitourinary tracts, abnormal endocrine function, leukemia and leukemoid reactions. To provide better care for people with DS in Taiwan, we began the DS multi-disciplinary clinic that has opened once per month since November 2013. The multi-disciplinary clinic consists of several subspecialists who provide care for DS people. To date, approximately 200 patients have used the clinic. The average number of patients who use the clinic per month is 27±6 with a mean patient age of 16±12 years old (range 0.3-53 years). The average number of patients per specialist on each clinic day is 5.2±4.9 (range 0.5-20.9 patients). We focus on early detection and prevention of medical and developmental issues associated with DS. This coordinated approach allows DS patients and family to have more comprehensive care.

Postnatal Identification of Trisomy 21: An Overview of 7,133 Postnatal Trisomy 21 Cases Identified in a Diagnostic Reference Laboratory in China

This study describes the cytogenetic characteristics of 7,133 trisomy 21 (Tri21) identified from 247,818 consecutive postnatal cases karyotyped in a single reference laboratory in China for a period of 4 years. The average detection rate of Tri21 is 2.88% ranging from 3.39% in 2011 to 2.52% in 2014. The decreased detection rates over the years might reflect a possible impact of noninvasive prenatal testing applied rapidly in China and elective termination of affected pregnancies. 95.32% of the Tri21 karyotypes are standard Tri21, 4.53% are Robertsonian Tri21, and less than 1% are other Tri21 forms. There are more mosaic Tri21 in older children and adults, consistent with previous observations that clinical features in individuals with mosaic Tri21 are generally milder and easily missed during perinatal period. The male/female (M/F ratio) for the total 7,133 Tri21 cases and for the 6,671 cases with non-mosaic standard Tri21 are 1.50 and 1.53 respectively, significantly higher than the 0.93 for all the 247,818 cases we karyotyped, the 1.30 for the Down syndrome (DS) identified during perinatal period in China, and the 1.20 for the livebirth in Chinese population. In contrast, the mosaic standard Tri21 case has a significantly lower proportion of males when compared with the non-mosaic standard Tri21, indicating different underlying mechanisms leading to their formations. Opposite M/F ratios in different subtypes of ROB Tri21 were observed. A long list of rare or private karyotypes where Tri21 are concurrently present was identified. The large collection of Tri21 cases with a diversity of clinical findings and a wide age range allowed us to determine the frequency of the different karyotypes of Down syndrome in China, given the fact that this kind of national epidemiological data is lacking currently.

Recent trends in the birth prevalence of Down syndrome in China: impact of prenatal diagnosis and subsequent terminations

OBJECTIVE

This study aims to analyze recent trends in Down syndrome (DS) prevalence in China and evaluate the impact of prenatal diagnosis and subsequent terminations.

DESIGN

A birth defects surveillance-based retrospective study was adopted.

METHODS

On the basis of the 1996 to 2011 surveillance data for DS from Chinese Birth Defects Monitoring Network, we examined the total prevalence ratio (TPR), perinatal prevalence ratio (PPR) and percentages of prenatally identified cases and of terminations by periods (before and after 2003), birth area, gender and maternal-age classifications.

RESULTS

Down syndrome TPR was 3.05 per 10 000 births during 2003 to 2011, with significant differences between urban-rural, gender and maternal-age groups. DS PPR during 1996 to 2011 was 1.99 per 10 000, presenting an increasing trend till 2003 but a decreasing tendency since then. The proportion of DS diagnosed prenatally increased from 7.55% during 1996 to 2002 to 47.70% during 2003 to 2011, varying by birth area and maternal age. During 2003 to 2011, the high termination rate led to 55% reduction in the overall DS PPR and 62% and 36% decreases in urban and rural PPRs.

CONCLUSION

The important reduction in the PPR suggests that current strategies in China for the prenatal screening and diagnosis of DS are effective. However, significant urban-rural variations in TPR and PPR indicate an urgent need to strengthen prenatal care for DS in rural regions.

Extended First-Trimester Screening Using Multiple Sonographic Markers and Maternal Serum Biochemistry: A Five-Year Prospective Study

<b><i>Objective:</i></b> To examine the performance of first-trimester screening test combining several fetal sonographic and maternal biochemical markers for major aneuploidy in a Chinese population. <b><i>Methods:</i></b> This was a prospective study performed over 5 years between January 2005 and December 2010 in Taiwan, with 20,586 cases that had a combination of a variety of sonographic markers and maternal serological β-human chorionic gonadotropin and pregnancy-associated plasma protein-A levels assessed at first trimester screening between 11⁺⁰ and 13⁺⁶ weeks of gestation. The risk of aneuploidy was calculated using algorithm software developed by Fetal Medicine Foundation, London. Fetal karyotyping was performed when the prenatal screening showed a risk of 1/300 or higher. All cases were followed for fetal outcome. <b><i>Results:</i></b> The study population was divided into four groups according to the screening strategy performed. The combination of maternal serological biochemistry and nuchal translucency measurement had a 66.7% detection rate of trisomy 21. Addition of nasal bone status increased the detection rate of trisomy 21 to 88.2%. Inclusion of tricuspid regurgitation flow showed an 87.5% detection rate of trisomy 21. Further inclusion of ductus venosus flow increased the detection rate of trisomy 21 to 100%. Incorporating more markers greatly increased the detection rate and decreased the false-positive rate (FPR). <b><i>Conclusion:</i></b> Extension of first-trimester screening to include more sonographic markers greatly increased the sensitivity and decreased FPR for detection of chromosomal abnormalities. Such screening strategy is effective in clinical practice for the Chinese ethnic population.

The impact of Down syndrome screening on Taiwanese Down syndrome births: a nationwide retrospective study and a screening result from a single medical centre

A retrospective analysis of the Taiwanese National Birth Defect Registration and Notification System was conducted in order to determine the live birth- and stillbirth rates in infants with Down syndrome, trisomy 18, trisomy 13 and Turner syndrome between 2001 and 2010. The objective was to investigate the impact of Down syndrome screening on the Taiwanese Down syndrome live birth rate. In addition, the results of first-trimester Down syndrome screening between 2006 and 2011, and of second-trimester quadruple testing between 2008 and 2011, were obtained from the National Taiwan University Hospital. All Taiwanese infants born between 2001 and 2010 were included in the first part of the analysis, and women receiving first-trimester Down syndrome screening or second-trimester quadruple testing from the National Taiwan University Hospital were included in the second part. The live birth rate of infants with Down syndrome, per 100 000 live births, decreased from 22.28 in 2001 to 7.79 in 2010. The ratio of liveborn DS to total DS was 48.74% in 2001, and then decreased to 25.88% in 2006, when first-trimester screening was widely introduced in Taiwan. This ratio dropped to 20.64% in 2008, when the second-trimester quadruple test was implemented. The overall positive rate in first-trimester screening in the National Taiwan University Hospital was 3.1%, with a Down syndrome detection rate of 100%; the quadruple test had values of 9.0% and 75%, respectively. The use of first-trimester screening and the second-trimester quadruple test may be responsible for the marked decrease in the Taiwanese Down syndrome live birth rate observed between 2001 and 2010.

Development of genetic counseling services in Taiwan

Taiwan is an emerging industrial country in subtropical Asia with a population of 23 million. There were around 200,000 newborns in 2011. Delayed first marriage, low birth rate, and rapid aging are major demographic issues. Genetic counseling services were established following the rapid introduction of genetic technology and enactment of relevant laws and regulations. Ultrasound was first used in 1968 to examine pregnant women. The first amniotic fluid laboratory was founded in 1981 to identify chromosomal abnormalities. In 1984, the Genetic Health Act was legislated for prevention and control of genetic disorders, and the metabolic disorder screen project was launched. National Health Insurance with overall coverage of prenatal examinations was established in 1995. A master-level genetic counseling program was launched in 2003 and by 2011 has graduated eighty students. Two professional societies have been formed to certify genetic counselors, and 66 professionals have been certified. In summary, genetic counseling services in Taiwan are continuously improving.

Retrospective analysis of live birth prevalence of children with Down syndrome in Denizli, Turkey

Down syndrome (DS) is the most frequent chromosome abnormality among live births. Its prevalence increases with maternal age, and can be diagnosed by antenatal screening. We examined prevalence variations of DS in Denizli, Turkey, through a retrospective study. Sixteen years of survey data were retrieved from the two main state hospital registries from records between 1994 and 2010. We identified 113 DS live births in Denizli for 16 years. The prevalence of DS was 9.07 per 10,000 live births before the year 2000 and 9.90 after 2000. The prevalence did not change significantly. The population in Turkey is still young; the fertility rate is high in women under 35 years old and prenatal screening programs are extensively applied; for these reasons, the prevalence of DS has remained stable during these 16 years.

Distinct clinical characteristics of patients with congenital duodenal obstruction in a medical center in Taiwan

BACKGROUND

Patients with congenital duodenal obstruction (CDO) predominantly have a postampullary lesion site and a high association with Down syndrome, according to previous reports from Western countries. This study aimed to determine whether there are racial differences in the clinical characteristics of congenital duodenal obstruction, based on the experience from a Taiwanese medical center.

METHODS

The charts were retrospectively reviewed among neonates with CDO who received surgery at National Taiwan University Hospital during the period 1985- 2008. Patients were grouped into a preampullary or postampullary group according to the obstruction in relation to the ampulla of Vater. Other characteristics, including sex, time of diagnosis, operative findings, as well as associated anomalies, were recorded for further analysis.

RESULTS

A total of 30 patients with CDO including 16 with atresia, 10 with mucosal webs, and 4 with stenosis, were recruited; among them, 16 were boys and 14 were girls. In 15 patients (50%), the diagnosis of duodenal obstruction was made prenatally. A total of 11 of the 30 patients (37%) were in the preampullary group and 19 (63%) were in the postampullary group. Seventeen patients (56.7%) had at least one additional anomaly, including four (13%) who had trisomy 21. The preampullary group had significantly fewer associated congenital anomalies than in the postampullary group (27%vs. 74%, p = 0.012).

CONCLUSION

Our cohort showed a relatively lower incidence of postampullary lesions and associated Down syndrome in patients with CDO compared with Western countries. Additionally, patients with preampullary lesions had significantly less association with other anomalies.

Uptake of prenatal diagnostic testing and the effectiveness of prenatal screening for Down syndrome

OBJECTIVES

To map prenatal screening and diagnostic testing pathways in Victorian pregnant women during 2003 to 2004; measure the impact of prenatal diagnostic testing uptake on the effectiveness of prenatal screening for Down syndrome; and assess factors influencing uptake of diagnostic testing following screening.

METHODS

State-wide data collections of prenatal screening and diagnostic tests were linked to all Victorian births and pregnancy terminations for birth defects.

RESULTS

Overall, 52% of women had a prenatal test (65 692/126 305); screening (44.9%), diagnostic testing (3.9%), or both (3.2%). Uptake of diagnostic testing was 71.4% (2390/3349) after an increased risk screen result, and 2.5% (1381/54 286) after a low risk result. Variation in uptake of diagnostic testing reduced the effectiveness of the screening program by 11.2%: from 87.4% (sensitivity - 125/143) to 76.2% (prenatal diagnoses of Down syndrome - 109/143). In both the increased and low risk groups, uptake was influenced by absolute numerical risk, as well as by the change in numerical risk from a priori risk.

CONCLUSIONS

This comprehensive follow-up demonstrates clearly that numerical risk is being used to aid in decision making about confirmatory diagnostic testing. Collectively, these fundamental individual decisions will impact on the overall effectiveness of screening programmes for Down syndrome.

Second-trimester maternal serum quadruple test for Down syndrome screening: a Taiwanese population-based study

OBJECTIVE

To assess the usefulness of quadruple test screening for Down syndrome in Taiwan.

MATERIALS AND METHODS

Maternal serum concentrations of alpha-fetoprotein, human chorionic gonadotropin, unconjugated estriol, and inhibin A were measured in 21,481 pregnant women from 15 to 20 weeks of gestation.

RESULTS

Of the 21,481 women, 977 returned values greater than the high-risk cut-off value (1 in 270). Most of these women (86.2%) decided to have an invasive procedure for genetic diagnosis. Nine cases of Down syndrome and 19 cases of other chromosomal anomalies were detected prenatally. Two children with Down syndrome were diagnosed after delivery even though a low estimated risk was determined following the quadruple test. The detection rate was 81.8% (nine out of 11 cases), with a 4.4% false-positive rate. The median multiple of the median value for a-fetoprotein, human chorionic gonadotropin, unconjugated estriol and inhibin A were 0.87, 2.34, 0.77 and 2.16, respectively, in affected cases.

CONCLUSION

This is the first study of the quadruple test for Down syndrome in a Chinese population. Our findings suggested that the second-trimester quadruple test provides an effective screening tool for Down syndrome in Taiwan.

First-trimester Down syndrome screening in women younger than 35 years old and cost-effectiveness analysis in Taiwan population

OBJECTIVES

Outcome of the first-trimester Down syndrome screening in younger population was less reported before. We present the outcome of this screening in Taiwanese women younger than 35 years old. We also test whether or not the first-trimester Down syndrome screening of women <35 years of age and women >35 years old routinely receiving amniocentesis is cost-effective compared with all pregnant women screened with this test in the setting of increased maternal age.

METHODS

From 1999 to 2007, the first-trimester Down syndrome screening including nuchal thickness, pregnancy-associated plasma protein A and free beta-hCG are provided to 10 811 singleton women <35 years of age with the cut-off of 1/270. A cost-effectiveness analysis of young women receiving this screening and older women undergo amniocentesis versus all women undergo this screening was performed in Taiwan population from 1987 to 2006, in which advanced age pregnancies increased from 2.8% to 11.6% of total pregnancies.

RESULTS

Detection rates of trisomy 21, trisomy 18, Turner syndrome and other chromosome anormalies in women <35 years of age are 87.5% (14/16), 50% (2/4), 80% (8/10) and 63% (12/19), respectively, with a false-positive rate of 5.5% (590/10 811). As advanced age pregnancies reached 11.6%, the average cost per one case averted for all women screened ranged from $77 204 to $98 421, while the cost ranged from $99 647 to $116 433 for only women <35 years of age receiving this screening.

CONCLUSIONS

In an aging population, the first-trimester Down syndrome screening should be implemented for all pregnant women when it is available.

Meiosis in oocytes: predisposition to aneuploidy and its increased incidence with age

Mammalian oocytes begin meiosis in the fetal ovary, but only complete it when fertilized in the adult reproductive tract. This review examines the cell biology of this protracted process: from entry of primordial germ cells into meiosis to conception. The defining feature of meiosis is two consecutive cell divisions (meiosis I and II) and two cell cycle arrests: at the germinal vesicle (GV), dictyate stage of prophase I and at metaphase II. These arrests are spanned by three key events, the focus of this review: (i) passage from mitosis to GV arrest during fetal life, regulated by retinoic acid; (ii) passage through meiosis I and (iii) completion of meiosis II following fertilization, both meiotic divisions being regulated by cyclin-dependent kinase (CDK1) activity. Meiosis I in human oocytes is associated with an age-related high rate of chromosomal mis-segregation, such as trisomy 21 (Down's syndrome), resulting in aneuploid conceptuses. Although aneuploidy is likely to be multifactorial, oocytes from older women may be predisposed to be becoming aneuploid as a consequence of an age-long decline in the cohesive ties holding chromosomes together. Such loss goes undetected by the oocyte during meiosis I either because its ability to respond and block division also deteriorates with age, or as a consequence of being inherently unable to respond to the types of segregation defects induced by cohesion loss.

The prevalence of live birth Down syndrome in the region of Primorsko-goranska County in Croatia, 1996-2005: the impact of screening and amniocentesis

OBJECTIVES

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.

METHODS

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.

RESULTS

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%.

CONCLUSIONS

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.

Descriptive epidemiology of Down's syndrome in Estonia

The aim of the study was to investigate the livebirth prevalence of Down's syndrome (DS) in Estonia during the past 14 years, create a DS database and observe the effectiveness of prenatal screening. This is a population-based descriptive study. The study subjects were children with DS diagnosis born between the years 1990 and 2003. We collected data from genetic centres in Estonia, from the databases of DS support groups, from institutions for disabled children and from the registers of family doctors/paediatricians. Prenatal screening for chromosomal anomalies for women aged >or=35 years was started in Estonia in 1995. Therefore, we divided the DS children into two groups: 112 born between 1990 and 1994 comprise group I, and 127 born between 1995 and 2003 comprise group II. Group II was further divided into two subgroups: IIa, from 1995 to 1998, when screening of advanced maternal age (>or=35 years) commenced, and IIb, from 1999 to 2003, when screening of second trimester maternal serum for younger women commenced. Prenatally, 68 cases of DS were diagnosed between 1995 and 2003 in the whole of Estonia, and all of these pregnancies were terminated. This represents 34.9% of all delivered and prenatally detected DS cases from this period. The overall livebirth prevalence was 1.17 per 1000 livebirths. The livebirth prevalence in group I was 1.25 and in group II was 1.09 per 1000 livebirths. The second trimester maternal serum screening with advanced maternal age screening was more effective than advanced maternal age screening alone. The livebirth prevalence in group IIa was 1.22 and in group IIb 0.99 per 1000 livebirths. Overall, regular trisomy was found in 90.4%, translocation in 6.3% and mosaicism in 2.9%. The overall male to female sex ratio of DS was 1.09.