Prenatal Diagnosis of Trisomy 21: Registration Results from a Single Genetic Center

By Witters, I.; Fryns, J. P. | Genetic Counseling, April 1, 2008 | Go to article overview

Prenatal Diagnosis of Trisomy 21: Registration Results from a Single Genetic Center


Witters, I., Fryns, J. P., Genetic Counseling


Summary: Prenatal diagnosis of trisomy 21: registration results from a single genetic center: This is a retrospective review of all collected amniotic fluid samples, chorionic villus samples and other fluid-aspirations (hygroma colli fluid/ urine from megacystis) over an 11-year period (1996-2006) in a single Genetic Center (University Hospital Gasthuisberg, Leuven), looking at the prenatal diagnosis of trisomy 21. In this study a total of 404 diagnoses of trisomy 21 were made on 29696 samples (1.4%). The prenatal diagnosis of trisomy 21 increased over the years with 0.88% (21/2363) in 1996 and 1.99% (50/2512)in 2006. Also the type of invasive testing changed over the years with an increase of the proportion of trisomy 21- diagnoses by chorionic villussampling from 2001.

Looking at the registry for perinatal activities in Flanders for the year 2006 the live birth incidence for trisomy 21 was 1/1782 and this is lower than the often reported incidence of trisomy 21 at birth of 1/800: it is likely that the use of more sensitive screening methods for the prenatal detection of trisomy 21 and the election of termination for most affected pregnancies affects the birth incidence of trisomy 21.

Key-words: Trisomy 21 - Prenatal diagnosis

INTRODUCTION

Trisomy 21 is the most frequent chromosomal abnormality at birth with a reported incidence of 1/800 births. The incidence in the prenatal period is higher since the intrauterine lethality of trisomy 21 is 40 % between 12 and 40 weeks.

In this retrospective review we looked at the prenatal diagnosis of trisomy 21 in an eleven-years period (1996-2006) in the Center for Human Genetics in Leuven.

MATERIAL AND METHODS

All prenatal samples from invasive testing (chorionic villus sampling - amniocentesis - fluid from hygroma colli/ megacystis) sent for karyotyping to the Center for Human Genetics from the University hospital Leuven were reviewed for the period January 1996 -December 2006. The samples with diagnosis 'trisomy 21' were analyzed.

RESULTS

In the period January 1996-December 2006 a total number of 29696 prenatal samples were analyzed. These 29696 samples included 27888 amniocenteses, 1788 chorionic villus samplings and 20 samples on other fetal fluids (hygroma colli-fetal urine in case of megacystis).

In this period 404 diagnoses of trisomy 21 were made prenatally (1.4%). 391 cases were classical trisomy 21,3 cases involved mosaic trisomy 21 and 10 cases were the consequence of an unbalanced Robertsonian translocation. The indications for invasive testing in the 404 trisomy 21 diagnoses are given in table I.

Table II gives the indications for karyotyping and the type of translocation for the 10 translocation trisomies, of which 9 were de-novo unbalanced robertsonian translocations and one the unbalanced product of a maternal balanced Robertsonian translocation .

In Table III an overview of trisomy 21 diagnoses/year is given together with the sampling method (amniocentesis-cvs-other fluids). Of the 404 trisomy 21 diagnoses, 87 were made by chorionic villus sampling (87/404 = 21.5%), 7 by puncture of hygroma colli (n = 3/6)/megacystis (n = 4/14) (7/404 = 2%) and 310 were made by amniocentesis (310/404 = 76.7%). Of the 1788 chorionic villus samplings performed 87 trisomy 21 cases were diagnosed (4.9 %) and for the amniocenteses this was 310/27888 (1 %). Puncture of hygroma colli fluid revealed 3 trisomy 21 on 6 samples (50 %) and for megacystis 4 trisomy 21 on 14 samples (29 %). Of the 404 trisomy 21 diagnoses 213 (53 %) were male and 191 (47 %) were female .

DISCUSSION

This is a retrospective review of all collected amniotic fluid samples, chorionic villus samples and other fluid-aspirations (hygroma colli fluid/ urine from megacystis) over a 11-year period (1996-2006) in a single Genetic Center (University Hospital Gasthuisberg, Leuven), looking at the prenatal diagnosis of trisomy 21. …

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