Try For A Larger Hospital When Taking Invasive Tests
A recent study of over 64,000 pregnant women showed that the respective rates of miscarriage after amniocentesis and chorionic villus sampling (CVS) are 1.4% and 1.9%. The results of this study, published in the July 2009 issue of Ultrasound in Obstetrics and Gynecology, suggest that the number of these procedures performed by a given department has a significant impact on rates of miscarriage following these invasive prenatal procedures.
The rate for miscarriage in departments performing fewer than 500 amniocentesis procedures spread over 11 years was 2.2 times higher than in departments in which at least 3 times the number of such procedures were performed during the same time period. By the same token, the rate of miscarriage after CVS was 1.5 times greater in facilities where 500-1,500 procedures were carried out as opposed to those facilities in which more than 1, 500 such procedures were performed.
Researchers from the Copenhagen University Hospital studied the results of amniocentesis and CVS tests performed in Denmark between 1996 and 2006 on singleton pregnancies. Of the 64,207 women, slightly more than 51% had an amniocentesis procedure and the rest received the CVS testing.
Lead author of the study, Professor Ann Tabor from the Department of Fetal Medicine, explained that all Danish citizens have personal identification numbers which helped the researchers determine under which health registry a given citizen received her care. This in turn meant that researchers were able to find chromosome analysis reports submitted to the Danish Central Cytogenic Registry and to cross-reference them to miscarriages, abortions, and deliveries registered in the National Registry of Patients. Miscarriage after these procedures was defined as spontaneous miscarriage or intrauterine death before the 24th week of gestation.
The preference for CVS as a diagnostic test over amniocentesis became apparent when researchers realized that the number of amniocentesis tests dropped from 55% to 31% during the 11 year period of the study. The number of CVS tests, on the other hand, rose from 49% to 69%. Professor Tabor explains that the increase in CVS tests is due to the fact that this test is offered four weeks before amniocentesis affording an earlier screening for birth defects.
The study was not able to evaluate which test proved less of a risk for miscarriage since other factors that contribute toward the total miscarriage rate become irrelevant with time. Because of this, it looks as though the risk of miscarriage after amniocentesis is lower than for that of CVS, but this appears to be a deceptive statistic. Other studies have shown the difference between the miscarriage rates for the two procedures to be negligible.