from the analysis of almost 1.5 million assisted reproductive technology (ART) cycles, and their affect may be very important in clinical practice, extreme caution in their interpreta- tion would be desirable. Data from the National ART Surveillance Sys- tem show a decrease of 43% in tubal infertility patients between 2000 and 2010. 2 This dramatic decline is ex- plained by the authors as the result of an increasing number of alternative indications for use of ART. However, no significant increase in other ART indication was observed over the past 11 years except for an increase of pa- tients with diminished ovarian reserve. 2 Furthermore, an absolute decline in number of the couples with tubal factor infertility also was observed. 1 The authors suggest that this decline may result from the decrease in the rates of pelvic inflam- matory disease in the United States that started in the 1980s. 1 However, by analyzing data from the National ART Surveillance System, it emerges that the decline in the number of cou- ples with tubal factor infertility is restricted to past 5 years. 2 Moreover, the prevalence of Chlamydia trachomatis infection, the primary cause of tubal factor infertility, has been increasing constantly over the past 30 years. 3 Regarding the association between tubal factor infertility and risk of adverse perinatal outcomes, it is a very important finding that should be addressed in the counseling of couples before starting in vitro fertil- ization treatment. However, further analysis should be conducted. For instance, in the present study, the influence on perinatal risk of selec- tive embryo reduction has not been taken into account. Similarly, it should be considered that a relevant bias might be represented by criteria used for the diagnosis of tubal and male factor infertility. Among the 443 U.S. ART clinics, the percentage of couples with tubal and male factor infertility ranged between 0% and 39% and between 0% and 59%, respectively. 2 In conclusion, because the informa- tion derived from this enormous data- base may significantly influence several areas of clinical practice, accurate anal- ysis of the data should be favored. Financial Disclosure: The authors did not report any potential conflicts of interest. Giuseppe Ricci, MD Institute for Maternal and Child Health, IRCCS “Burlo Garofolo” and, University of Trieste, Trieste, Italy Rita Boscolo, BSc Monica Martinelli, BSc Leo Fischer-Tamaro, MD Institute for Maternal and Child Health, IRCCS “Burlo Garofolo”, Trieste, Italy REFERENCES 1. Kawwass JF, Crawford S, Kissin DM, Session DR, Boulet S, Jamieson DJ. Tubal factor infertility and perinatal risk after assisted reproductive technology. Obstet Gynecol 2013;121:1263–71. 2. Centers for Disease Control and Preven- tion. 2011 Sexually transmitted diseases surveillance: STDs in women and infants. Available at: http://www.cdc. gov/std/stats11/womenandinf.htm#foot20. Retrieved August 1, 2013. 3. Centers for Disease Control and Preven- tion. CDC grand rounds: chlamydia pre- vention: challenges and strategies for reducing disease burden and sequelae. MMWR Morb Mortal Wkly Rep 2011; 60:370–3. In Reply: We appreciate Dr. Kamphuis et al’s and Dr. Ricci et al’s interest in our article. 1 We agree that male factor infertility incorporates a range of dis- ease severity. Findings from a recent study indicate no association between male factor infertility and perinatal outcome. 2 The rate of intracytoplas- mic sperm injection use in our study was not surprising; in 2010, intracyto- plasmic sperm injection was used in 66% of fresh, nondonor in vitro fertil- ization cycles in the United States, regardless of infertility diagnosis. 3 We agree that surveillance data are limited by the lack of some historical medical information, and this was noted as a limitation in the article. The aim of this observational study was not to suggest causality but to evaluate a potential association. Although we were unable to separate iatrogenic from spontaneous preterm birth, we did stratify by early-preterm and late- preterm birth because most iatrogenic preterm birth occurs at later gestational ages. After stratification, the association between tubal factor infertility and preterm birth remained. Although pro- pensity scores could have been used to account for possible confounding by obstetric history and maternal age, its use would have reduced the sample size, depending on the closeness of the matching algorithm. We considered regression analysis to be preferable because it is an established and accepted tool for evaluation of confounding and allowed us to capitalize on the large study population. We maintain that the decrease in the percentage of total assisted reproduc- tive technology cycles holding a tubal factor diagnosis reflects increased alter- native indications such as diminished ovarian reserve. Although Chlamydia trachomatis rates have increased, hospi- tal admissions for pelvic inflammatory disease have decreased. 4 Pelvic inflam- matory disease, rather than chlamydial infection, may explain more accurately the decrease in absolute number of tubal factor cycles. Regarding the potential effect of selective reduction, our analysis demonstrated an associa- tion between poor perinatal outcome and tubal disease among singleton pregnancies after controlling for num- ber of fetal heartbeats at first ultrasound scan. Our study should be interpreted with care and is subject to several limitations. Future studies that include additional preterm birth risk factors may help to delineate the association between tubal disease and preterm birth. Financial Disclosure: The authors did not report any potential conflicts of interest. Jennifer F. Kawwass, MD Division of Reproductive Endocrinology and Infertility, Department of Gynecology and Obstetrics, Emory University School of Medicine and, Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia Sheree Boulet, DrPH, MPH Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia VOL. 122, NO. 4, OCTOBER 2013 Letters to the Editor 909