Volume 188, Number 2 Letters 601Am J Obstet Gynecol

range reported in the literature. Despite high-quality datadescribing a procedure-related pregnancy loss rate of0.5% to 1.0%,2-4 they suggest statistical comparisons ofour data to patient information pamphlets. This is com-pared with the procedure-related losses of Blessed et al of2.2% for “generalists” and 0.3% for “perinatologists”(their primary outcome variable was pregnancy loss [attheir hospital] within 30 days of the procedure, ratherthan overall pregnancy loss). However, given the inabilityof Blessed et al to adequately describe their populationand their selection of a surrogate outcome, it is somewhatproblematic to make even subjective comparisons of ourdata with either of their groups.

A major reason we performed our study was that wefelt, on the basis of their data, that their conclusionswere overstated and their comments struck us as unnec-essarily inflammatory, especially the use of the phrase“misleading themselves and their patients.” The contin-ued use of such rhetoric by these investigators to de-scribe their observations is troublesome, especially in thecontext of such scientific limitations to their study. Be-cause others may inappropriately use these statementsfor either medicolegal or financial gain, it is my opinionthat better discretion should be exercised in future sci-entific discussions.

Until better studies are conducted, I will continue tocounsel patients and discuss with referring physicians inour area that I believe not every single genetic amniocen-tesis needs to be done by a subspecialist. I will also statethat training, expertise, and caseload are all probablymore important factors than whether the operator is ageneralist or a perinatologist. In my experience (al-though limited), most general obstetrician-gynecologistsuse good clinical judgment in this decision-makingprocess.

Sean C. Blackwell, MDDivision of Maternal Fetal Medicine, Department of Obstetrics and Gy-necology, Hutzel Hospital/Wayne State University, 4707 St AntoineBlvd, Detroit, MI 48201; e-mail: mfmboy@aol.com

REFERENCES

1. Blessed WB, Lacoste H, Welch RA. Obstetrician-gynecologistsperforming genetic amniocentesis may be misleading them-selves and their patients. Am J Obstet Gynecol 2001;184:1340-4.

2. Tabor A, Madsen M, Obel EB, Philip J, Bang J, Norgaard-Peder-sen B. Randomised controlled trial of genetic amniocentesis in4606 low-risk women. Lancet 1986;1:1287-93.

3. Canadian Early and Midtrimester Amniocentesis Trial (CEMAT)Group. Randomized trial to assess the safety and fetal outcomesof early and midtrimester amniocentesis. Lancet 1998;351:242-7.

4. National Institute of Child Health and Human Development Na-tional Registry for Amniocentesis Study Group. Midtrimesteramniocentesis for prenatal diagnosis: safety and accuracy. JAMA1976;236:1471-6.

doi:10.1067/mob.2003.45

Impact of single- or double-layer closure on uterineruptureTo the Editors: We read with great interest the report by Bu-jold et al1 regarding the increased risk for uterine rup-ture with single-layer compared with double-layer closure

of the uterus. In both the univariate analysis and in themultiple logistic regression, the authors evaluated the fac-tors most related to uterine rupture. In their evaluationof interdelivery interval, the authors defined a short in-terdelivery interval as 24 months or less. However, the twoprior studies cited by the authors as demonstrating the as-sociation of uterine rupture or “uterine scar failure”2 withshort interdelivery intervals2,3 both defined short inter-delivery intervals as approximately 16 to 18 months orless. Using the 24-month threshold could decrease themagnitude of the association of interdelivery intervalwith uterine rupture. In our data, we find that the risk ofuterine rupture was 2.25% for women with interdeliveryintervals of ≤18 months (7/311).3 In contrast, there wereno uterine ruptures among 393 women with interdeliveryintervals of 19 to 24 months. In addition, failure to prop-erly control for interdelivery interval could magnify theassociation of method of closure with risk of uterine rup-ture. Because use of a single-layer closure “gradually be-came the standard of practice”1 in the study of Bujold etal, women with short interdelivery intervals may havebeen more likely to have had a single-layer closure (be-cause the prior delivery was later in the evolution of prac-tice than for women with longer interdelivery intervals).Would it be possible for the authors to reanalyze theirdata with respect to interdelivery interval based on theprior literature?

Thomas D. Shipp, MD, and Ellice Lieberman, MD, DrPHDivision of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Brigham & Women’s Hospital, 75 Francis St, Boston, MA 02115

REFERENCES

1. Bujold E, Bujold C, Hamilton EF, Harel F, Gauthier RJ. The im-pact of a single-layer or double-layer closure on uterine rupture.Am J Obstet Gynecol 2002;186:1326-30.

2. Esposito MA, Menihan CA, Malee MP. Association of interpreg-nancy interval with uterine scar failure in labor: a case-controlstudy. Am J Obstet Gynecol 2000;183:1180-3.

3. Shipp TD, Zelop CM, Repke JT, Cohen A, Lieberman E. Inter-delivery interval and risk of symptomatic uterine rupture. ObstetGynecol 2001;97:175-7.

doi:10.1067/mob.2003.148

ReplyTo the Editors: We appreciate the comments of Drs Shippand Lieberman regarding the effect of the interdeliveryinterval on the risk of uterine rupture. Several considera-tions are important when a multivariate analysis is de-signed to measure the role of selected factors on aparticular outcome. For example, one can conclude onlyabout the factors that are selected, and, furthermore, aparticular factor may subsume a whole host of other re-lated but unmeasured issues. The study sample must besufficiently large and varied with various combinations ofthe factors so that the statistical methods can sort out theindependent effects of any one factor.

Before formulating the study design, we reviewed theliterature extensively to determine the best interdelivery