Single uterine entry for genetic amniocentesis in twin pregnancies.

In 176 diamniotic twin pregnancies at 10-20 weeks of gestation, amniotic fluid for cytogenetic studies was successfully obtained from both sacs by the use of a single uterine entry. There were no cases of discordancy between sex at amniocentesis and birth. There were six pregnancies with fetal unbalanced chromosomal defects; in one pregnancy both fetuses were abnormal and in five pregnancies only one fetus was abnormal. The total fetal loss rate was 5.7% (20 of 352 fetuses), including six (1.7%) terminations or selective fetocides and 14 (4.0%) spontaneous deaths. In the 176 pregnancies there were five (2.8%) with no survivors, including one termination and four (2.3%) spontaneous miscarriages or intrauterine deaths. There are only two (1.1%) pregnancies in which amniocentesis could have contributed directly to the losses and therefore the procedure-related rate of fetal loss may be similar to that in singleton pregnancies. The median gestation at delivery was 37 (range 16-40) weeks and delivery before 32 weeks occurred in 9% of the pregnancies. The birth weight distribution was similar to that reported in singleton pregnancies. This study demonstrates that in twin pregnancies amniotic fluid for cytogenetic studies can be obtained successfully from both sacs by use of a single uterine entry. The risk of fetal loss from this procedure appears to be similar to that in singleton pregnancies.