J Obstet Gynecol. 1993 Jul;82(1):49-56.
Prenatal diagnosis in twin gestations: a comparison
between second-trimester amniocentesis and
first-trimester chorionic villus sampling.
Wapner RJ, Johnson A, Davis G, Urban A, Morgan P,
Jackson L.
Department of Obstetrics and Gynecology, Jefferson
Medical College of Thomas Jefferson University Hospital,
Philadelphia, Pennsylvania.
Objectives:
To evaluate prospectively the relative risks
and accuracy of first-trimester chorionic villus
sampling (CVS) and second-trimester amniocentesis in the
genetic evaluation of twin gestations.
Methods:
Between
March 1984 and August 1990, patients presenting for
prenatal diagnosis of a twin gestation of less than 12
weeks were offered sampling by either first-trimester
CVS or amniocentesis at 16-18 weeks' gestation.
Selection was based solely on patient preference and was
obtained before ultrasound identification of placental
position. Women presenting beyond 12 weeks' gestation
were sampled by amniocentesis. Clinical and laboratory
outcomes were evaluated.
Results:
Eighty-one women had
amniocentesis (nine of whom also had CVS), and 161 women
had CVS. All fetuses in both groups were successfully
sampled and karyotyped; 85.3% of the amniocentesis
patients and 75.8% of the CVS patients were sampled in
two or fewer passes (P = not significant). There were
three cases of twin-twin villus contamination following
CVS; one of these led to incorrect gender assignment
because of erroneous laboratory interpretation. Loss of
the entire pregnancy from the time of sampling until the
28th week of gestation followed amniocentesis in 2.9% of
the cass and CVS in 3.2%. The total fetal loss rates
were 9.3% for amniocentesis and 4.9% for CVS (P = not
significant). When pregnancies having mosaic or abnormal
karyotype results are excluded, the total amniocentesis
loss rate remained 9.3% and the CVS loss rate became
3.9% (P < .05).
Conclusion:
In the hands of experienced
operators, CVS is at least as safe and effective as
amniocentesis for the prenatal diagnosis of twin
gestations.
