[Which invasive diagnostic procedure should we use for twin pregnancies: chorionic villous sampling or amniocentesis?]

Objective: To describe invasive diagnostic procedures (amniocentesis/choriocentesis) and subsequent risks in twin pregnancies.

Material and methods: PubMed and Cochrane database investigations were conducted using following key words: twin gestation, amniocentesis, chorionic villous sampling, karyotype. Guidelines for twin management edicted by different societies were reviewed.

Results: Risk of pregnancy loss after invasive diagnostic procedure in twin pregnancies seems to be slightly higher to singletons, i.e about 1.5-2% after mid-trimester amniocentesis and about 2% after first trimester choriocentesis. Dual sampling is not always mandatory but can be performed on parent's request. Specific risks are associated with twins: redundant sampling, permutation or misidentification of affected twin in case of discordant status. Procedures should be performed by highly-skilled operators under permanent ultrasound-guidance. A scheme describing placental locations and funicular insertions appears to be useful for correct identification. If foeticide can be anticipated, diagnostic procedure and foeticide should be performed by the same operators. For amniocentesis, one or two needles can be used except for cases with infectious disease (two needles and two separate insertions required). For choriocentesis, sampling should be performed close to funicular insertions.

Conclusion: First-trimester choriocentesis makes earlier diagnosis and earlier foeticide possible compared with mid-trimester amniocentesis. Both techniques require highly-skilled operators to reduce subsequent risks in the context of twin pregnancies.