Risk for fetal loss and prematurity after 12,413 second trimester amniocenteses in a single center.
S the introduction of second-trimester amniocentesis in clinical practice during the 1970s, the procedure has always been characterized as being very safe but associated with a low risk of causing pregnancy loss. Early collaborative studies in North America examined the safety and accuracy of this procedure.1,2 These studies were conducted at a time when many obstetricians did not have vast experience with the procedure and only a portion of patients had an ultrasound examination before the procedure. Real-time ultrasound guidance was not available as we currently use it. The frequency of pregnancy loss after amniocentesis was compared with control populations who did not choose to have genetic testing or compared with general population data. The total rate of pregnancy losses after amniocentesis was about 3.5% and was not significantly different from the controls. Based on the sizes of these studies, the results supported counseling patients that the risk of loss attributable to the procedure was less than 0.5%. The only randomized controlled trial of amniocentesis found a 1% excess risk loss due to the procedure.3 With the exception of the size of needles used in that study, the difference in findings compared with the collaborative trials has not been explained. Since the 1970s, second-trimester amniocentesis has been performed in hundreds of thousands of women worldwide. For many years clinicians have suspected that the rate of pregnancy loss after amniocentesis may be lower than reported in the early observational studies. This clinical impression could be the result of the upper limit of gestational age for observation of outcome or less rigorous monitoring of outcome by referral centers performing the procedure. It may also be attributable, in part, to improved gestational dating and the exclusion of patients with missed abortions and certain severe fetal malformations recognized by ultrasonography. It also seems likely that the rate of loss due to the procedure might be diminishing. Operators are generally much more experienced with the procedure, many use smaller-bore needles (eg, 22 gauge), and ultrasound guidance has improved dramatically. A recent report in this journal from a large multicenter collaborative screening trial (the First and Second Trimester Evaluation of Risk [FASTER]) indicated that the procedure-related risk of loss was 1:1,600 (0.06%).4 The safety of amniocentesis was not a primary end point of the study and the analysis, and interpretation of the data has stirred considerable controversy and debate. In this issue of the journal, Odibo et al (see p. 589) report yet another observational experience from a single institution conducted over 16 years. The rate of loss attributable to amniocentesis was 1:769 (0.13%).5 These findings and the methodology used are likely to fuel continued debate. An easy solution for us would be to estimate a safe middle ground between the traditional 0.5% risk and the risks observed in these recent See related article on page 589.