Early amniocentesis and chorionic villus sampling offer the only alternative to second trimester amniocentesis regarding availability of the result. Second trimester amniocentesis is performed from 16 weeks´ gestation on, chorionic villus sampling and early amniocentesis are performed between 9 and 14 weeks [1,3,4]. The target of this script was to asses a comparison regarding pregnancy loss rate and availability of results for second trimester amniocentesis (AC), early amniocentesis, transcervical and transabdominal chorionic villus sampling (CVS). Therefore a literature research was performed, which included only randomised trials comparing AC and CVS.
Both AC and CVS are invasive diagnostic screening methods that carry a certain risk of pregnancy loss. AC requires insertion of a needle through the abdominal wall and into the uterus to withdraw amniotic fluid. CVS is a biopsy procedure that involves removing a piece of tissue from the placenta. The taken samples are then cultured and chromosomes are analyzed to determine abnormalities associated with Down syndrome and other genetic diseases such as cystic fibrosis, Tay-Sachs disease and sickle cell disease.
After literature research second trimester amniocentesis (risk of pregnancy loss 0,2-1,1 %) is safer than transcervical CVS (risk of pregnancy loss 0,4-3,8 %) and early amniocentesis (risk of pregnancy loss 1,9-4,7 %) [1,2,3,5]. If earlier diagnosis than 16 weeks of gestation is required, transabdominal CVS (risk of pregnancy loss 0,5-1,4 %) is preferable to early amniocentesis or transcervical CVS because of lower risk [1,3]. In circumstances where transabdominal CVS may be difficult, the preferred options are transcervical CVS in the first trimester or amniocentesis in the second trimester. It has always to be taken into account that the risk of miscarriage decreases when the practitioner have become more proficient with the procedures [4].
Patients who will undergo antenatal diagnostics should be informed in detail about risks and benefits of the alternative procedures before they make a choice. Second trimester AC is safer than transcervical CVS or early AC and benefits of earlier diagnosis must be set against its greater risks.
In future patients will hopefully have more choices in becoming serious results about the health of their fetus. There is a need of procedures which are less risky for both mother and fetus without loosing any quality of the results. Until then every patient has to decide individually whether she wants an invasive diagnostic or not and which procedure she will trust most.
Current developments concentrate on thinner diameter for the hollow needles (such as 25, 27 or even 29 Gauge) or on blood sampling from the mother. It will be interesting to follow these and other developments in antenatal diagnostics.
References:
- Brunner Bettina, Vergleich von Amniocentese und Chorionzottenbiopsie in Bezug auf Eingriffsrisiko, Aussagekraft und Dauer der humangenetischen Untersuchungsmethoden; Diplomarbeit; Akademie für den medizinisch-technischen Laboratoriumsdienst am Allgemeinen Krankenhaus der Stadt Wien
- Guideline of amniocentesis and chorionic villus sampling; Royal College of Obstetriciens and Gynaecologists; Guideline No. 8; Revised January 2005
- Alfirevic Z, Sundberg K, Brigham S; Amniocentesis and chorionic villus sampling for prenatal diagnosis; 2007 The Cochrane Collaboration. Published by JohnWiley & Sons, Ltd
4. Nancy Chan 2006; Study shows prenatal diagnostic tests have low risk of miscarriage; http://news.ucsf.edu/releases/study-shows-prenatal-diagnostic-tests-have-low-risk-of-miscarriage/
- Denise Pelikan, Humphrey Kanhai et al.; Fetomaternal hemorrhage in relation to chorionic villus sampling revisited; Prenatal Diagnostics in press