Prevalence and risk of Down syndrome in monozygotic and dizygotic multiple pregnancies in Europe: implications for prenatal screening.
OBJECTIVE
To determine risk of Down syndrome (DS) in multiple relative to singleton pregnancies, and compare prenatal diagnosis rates and pregnancy outcome.


METHODS
Population-based prevalence study based on EUROCAT congenital anomaly registries.


METHODS
Eight European countries.


METHODS
14.8 million births 1990-2009; 2.89% multiple births.


METHODS
DS cases included livebirths, fetal deaths from 20 weeks, and terminations of pregnancy for fetal anomaly (TOPFA). Zygosity is inferred from like/unlike sex for birth denominators, and from concordance for DS cases.


METHODS
Relative risk (RR) of DS per fetus/baby from multiple versus singleton pregnancies and per pregnancy in monozygotic/dizygotic versus singleton pregnancies. Proportion of prenatally diagnosed and pregnancy outcome.


METHODS
Poisson and logistic regression stratified for maternal age, country and time.


RESULTS
Overall, the adjusted (adj) RR of DS for fetus/babies from multiple versus singleton pregnancies was 0.58 (95% CI 0.53-0.62), similar for all maternal ages except for mothers over 44, for whom it was considerably lower. In 8.7% of twin pairs affected by DS, both co-twins were diagnosed with the condition. The adjRR of DS for monozygotic versus singleton pregnancies was 0.34 (95% CI 0.25-0.44) and for dizygotic versus singleton pregnancies 1.34 (95% CI 1.23-1.46). DS fetuses from multiple births were less likely to be prenatally diagnosed than singletons (adjOR 0.62 [95% CI 0.50-0.78]) and following diagnosis less likely to be TOPFA (adjOR 0.40 [95% CI 0.27-0.59]).


CONCLUSIONS
The risk of DS per fetus/baby is lower in multiple than singleton pregnancies. These estimates can be used for genetic counselling and prenatal screening.
EUROCAT Central Registry, Centre for Maternal Fetal and Infant Research, Institute for Nursing and Health Research, University of Ulster, Newtownabbey, UK.
B
B
Boyle
J K
JK
Morris
R
R
McConkey
E
E
Garne
M
M
Loane
M C
MC
Addor
M
M
Gatt
M
M
Haeusler
A
A
Latos-Bielenska
N
N
Lelong
R
R
McDonnell
C
C
Mullaney
M
M
O'Mahony
H
H
Dolk
D000328:Adult; D004314:Down Syndrome / Q000175:diagnosis* / Q000453:epidemiology*; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D011296:Prenatal Diagnosis; D015995:Prevalence; D012306:Risk; D018570:Risk Assessment; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D055815:Young Adult
Concordance; Down syndrome; monozygotic and dizygotic pregnancies; multiple births; pregnancy outcomes; twins