GENETIC AMNIOCENTESIS IN BIAMNIOTIC TWIN PREGNANCIES BY A SINGLE TRANSABDOMINAL INSERTION OF THE NEEDLE

We present a technique to aspirate amniotic fluid from both sacs in bi amniotic twin pregnancies using a single abdominal insertion with a sp inal needle. It was successful in 48 out of 55 cases of biamniotic twi n pregnancies referred to our perinatal unit between 1985 and 1994. Th e single insertion technique was used when the inter-amniotic membrane was clearly evident and two separate free amniotic fluid pools could be reached by the operator with a single puncture. An adequate amount of amniotic fluid was sampled from both sacs to make a cytogenetic dia gnosis in all cases. There were four fetuses with trisomy 21 in three twin pregnancies. In two cases, only one twin was affected whilst the co-twin was normal, so that a selective feticide was performed. No mis carriages due to genetic amniocentesis were reported. After 1990, all genetic amniocenteses in biamniotic twin pregnancies genetic (except f or one case due to late booking) were performed between 14 and 15 week s of gestation and with all cases except one, it was possible to sampl e both twins by a single puncture. We suggest that early amniocentesis (14-15 weeks) by a single abdominal puncture could be a reliable and safe alternative to first-trimester chorionic villus sampling in twin pregnancies.