[Risk of abortion following genetic amniocentesis in the 2d trimester in twin pregnancies].

Though the risk of abortion after amniocentesis in singleton pregnancies is well known, that for twin pregnancies is still unclear. A retrospective study was performed during December 1985 to May 1989 on all twin pregnancies that had undergone an amniocentesis, because of advanced maternal age. Out of the 33 patients aged greater than or equal to 35 years with viable and sonographically normal foetuses at the time of amniocentesis, three aborted spontaneously within 28 weeks of gestation, representing a risk of abortion after amniocentesis of 9.1%; using a cut-off at 20 weeks of gestation, only two patients aborted, giving a risk figure of 6.1%. This is 3.6 times higher than in singleton pregnancies (1.7%). However, to evaluate the procedure-related risk of amniocentesis, the age-dependent spontaneous abortion risk in twin pregnancies has to be considered. Accepting a spontaneous abortion risk of 4.5% after 16 weeks of gestation we have to calculate an amniocentesis-dependent risk of 1.6% up to the 20th week of gestation. It is essential, that the obviously higher genetic risk in twin pregnancies and the risk of procedure should be discussed carefully, before a patient with a twin pregnancy is advised to undergo genetic amniocentesis.