The timing of demise in fetuses with trisomy 21 and trisomy 18

Women with chromosomally abnormal fetuses often choose to continue their pregnancy. However, though they may search for specific details whether their fetus will survive, not much information is available. We sought to determine if there was a pattern for timing of demise and to determine if demise was more likely to occur before viability in fetuses with amniocentesis confirmed trisomy 18 or 21.

From the California Expanded AFP screening program, 1813 women were identified to have a fetus with trisomy 18 or 21. Of these, 392 women with trisomy 21 and 106 with trisomy 18 continued the pregnancy. Pregnancies ending in fetal demise were analyzed for gestational age at demise.

Of the trisomy 21 fetuses, 40 (10.2%) demised and of the trisomy 18 fetuses, 34 (32.1%) demised. The mean gestational age at time of fetal demise was 28.9+/-1.3 weeks SE for trisomy 21 and 32.1+/-1.2 weeks SE for trisomy 18 (p=0.09). There was no clustering of losses as losses were uniformly distributed throughout gestation after 24 weeks. A slightly larger proportion of T-21 (37.1%) losses occurred before viability (24 weeks) compared to those with T-18 (14.8%) (p=0.05).

It appears that after 24 weeks' gestation, there is no specific time for fetal demise in fetuses affected by trisomy 21 or 18. There may be an association between trisomy 21 and stillbirth prior to viability. This information may be helpful in counseling those patients found to have a chromosomally abnormal fetus who choose to continue their pregnancy.