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High-dose oxytocin
240
July 1996 AmJ ObstetGynecol
Letters
kinase levels to evaluate the sensitivity and the specificity of creatine kinase as a marker for tubal pregnancy and to decide which level is the precise and helpful cutoff value for the diagnosis of tubal pregnancy. Meanwhile, we believe that creatine kinase, especially in early pregnancy, can serve as an additional marker for the diagnosis of tubal pregnancy. Ofer Lavie, MD, Menachem Neuman, MD, and Uziel Beller, MD Department of Obstetricsand Gynecology,Division of GynecologicSurgery and Oncology, ShaareZedekMedical Cent~ P.O. Box 3235, Jerusalem, 91031 Israel
REFERENCES 1. Duncan WC, Sweeting VM, Cawood P, Illingworth PJ. Measurement of creatine-kinase activity and diagnosis of ectopic pregnancy. BrJ Obstet Gynaecol 1995;102:233-7. 2. Chandra L, Jain A. Maternal serum creatine kinase as a biochemical marker of tubal pregnancy. Int J Obstet Gynecol 1995;69:21-3. 3. Ponge S, Kurzel R. Creatine kinase and ectopic pregnancy [letter]. AmJ Obstet Gynecol 1995;172:1065-6.
6/8/74294
High-dose oxytocin To the Editors: We read with interest the article by Xenakis et al. (Xenakis EM-J, Langer O, Piper JM, Conway D, Berkus MD. Low-dose versus high-dose oxytocin augmentation of lab0r--A randomized trial. Am J Obstet Gynecol 1995;173:1874-8). In this important study the authors report that a high-dose oxytocin regimen results in a significant lowering of the cesarean section rate compared with a cohort receiving a low-dose oxytocin regimen. The study brings important information to the continuing debate of whether a high-dose or low-dose oxytocin protocol is optimal. Unfortunately, there appear to be two errors in the statistical methods. Specifically, the authors reported odds ratios rather than relative risks, as indicated in the article. The rate for cesarean delivery in the low-dose oxytocin group was 25.6% (40/156) compared with 10.4% (16/154) in the high-dose group. The correct relative risk is 2.47 and 95% confidence interval 1.44 to 4.22; the authors reported a relative risk of 2.97, which is actually the odds ratio. For nulliparous women the low-dose oxytocin group had a 27.7% (26/94) cesarean section rate compared with 11.1% (8/72) receiving high-dose oxytocin; the correct relative risk is 2.49, and 95% confidence intervals 1.20 to 5.17. For multiparous women the low-dose oxytocin group had a 22.6% (14/62) rate of cesarean delivery compared with 9.8% (8/82) for the high-dose oxytocin group; the correct relative risk is 2.31 and 95% confidence intervals 1.04 to 5.17. The authors performed 35 i n d e p e n d e n t statistical analyses in their study, which increases the likelihood of type I error. The use of either the Bonferroni method to adjust the accepted level of significance or the hierarchical approach would have been more desirable. ~
Mitchell P. Dombrowski, MD, and Sidney E Bottoms, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, WayneState University-HutzelHospital, 4707 St. Antoine Blvd., Detroit, M148201
REFERENCE 1. Godfrey KAM. Statistics in practice. N EnglJ Med 1985;313: 1450-6.
6/8/74296
Reply To the Editors: We read with interest the letter of Dombrowski and Bottoms. We appreciate the detail in which they analyzed our article, taking the time to recalculate the statistics. Indeed, the statistics reported in our study were odds ratios, inadvertently reported as relative risks. The Bonferroni method of correcting for multiple analyses is considered by many to be overly conservative; therefore we chose to report uncorrected p values to allow the reader to judge the significance for themselves. EUy M.-J. Xenakis, MD, Oded Lang~ MD, Jeanna M. Pip~ MD, Deborah Conway, MD, and Michael D. Berkus, MD Department of Obstetrics and Gynecology, University of Texas Health Center, 7703Floyd CurlDr., San Antonio, TX 78284-7836 6/8/74295
A "randomized" controlled trial without randomization To the Editors: The report by Xenakis et al. (Xenakis EM-J, Langer O, Piper JM, Conway D, Berkus MD. Low-dose versus high-dose oxytocin augmentation of labor A randomized controlled trial. A m J Obstet Gynecol 1995;173: 1874-8) misrepresents the research done. The title states that this was a randomized trial, yet the patients were not randomly allocated. The authors describe a sequential allocation by day of the week, which is not a random method)' 2 For example, patients enrolled on Mondays had a 100% probability of assignment to high-dose oxytocin rather than a 50% (or other fixed) probability, as would occur with random assignment.2 A more important problem with using day of the week for allocation is that it precluded concealment of the upcoming assignments. Recent research s has shown that failure to conceal the allocation sequence from those enrolling participants exaggerates the size of the treatm e n t effect by 30% to 40%, on average. Possible manifestations of these inadequacies in their allocation mechanism appear in their results. Because scheduled inductions of labor and elective cesarean births were apparently not included, roughly equal numbers of eligible patients each day of the week would be anticipated. Hence, with patients on 3 days of the week
July 1996 AmJ ObstetGynecol
Letters
kinase levels to evaluate the sensitivity and the specificity of creatine kinase as a marker for tubal pregnancy and to decide which level is the precise and helpful cutoff value for the diagnosis of tubal pregnancy. Meanwhile, we believe that creatine kinase, especially in early pregnancy, can serve as an additional marker for the diagnosis of tubal pregnancy. Ofer Lavie, MD, Menachem Neuman, MD, and Uziel Beller, MD Department of Obstetricsand Gynecology,Division of GynecologicSurgery and Oncology, ShaareZedekMedical Cent~ P.O. Box 3235, Jerusalem, 91031 Israel
REFERENCES 1. Duncan WC, Sweeting VM, Cawood P, Illingworth PJ. Measurement of creatine-kinase activity and diagnosis of ectopic pregnancy. BrJ Obstet Gynaecol 1995;102:233-7. 2. Chandra L, Jain A. Maternal serum creatine kinase as a biochemical marker of tubal pregnancy. Int J Obstet Gynecol 1995;69:21-3. 3. Ponge S, Kurzel R. Creatine kinase and ectopic pregnancy [letter]. AmJ Obstet Gynecol 1995;172:1065-6.
6/8/74294
High-dose oxytocin To the Editors: We read with interest the article by Xenakis et al. (Xenakis EM-J, Langer O, Piper JM, Conway D, Berkus MD. Low-dose versus high-dose oxytocin augmentation of lab0r--A randomized trial. Am J Obstet Gynecol 1995;173:1874-8). In this important study the authors report that a high-dose oxytocin regimen results in a significant lowering of the cesarean section rate compared with a cohort receiving a low-dose oxytocin regimen. The study brings important information to the continuing debate of whether a high-dose or low-dose oxytocin protocol is optimal. Unfortunately, there appear to be two errors in the statistical methods. Specifically, the authors reported odds ratios rather than relative risks, as indicated in the article. The rate for cesarean delivery in the low-dose oxytocin group was 25.6% (40/156) compared with 10.4% (16/154) in the high-dose group. The correct relative risk is 2.47 and 95% confidence interval 1.44 to 4.22; the authors reported a relative risk of 2.97, which is actually the odds ratio. For nulliparous women the low-dose oxytocin group had a 27.7% (26/94) cesarean section rate compared with 11.1% (8/72) receiving high-dose oxytocin; the correct relative risk is 2.49, and 95% confidence intervals 1.20 to 5.17. For multiparous women the low-dose oxytocin group had a 22.6% (14/62) rate of cesarean delivery compared with 9.8% (8/82) for the high-dose oxytocin group; the correct relative risk is 2.31 and 95% confidence intervals 1.04 to 5.17. The authors performed 35 i n d e p e n d e n t statistical analyses in their study, which increases the likelihood of type I error. The use of either the Bonferroni method to adjust the accepted level of significance or the hierarchical approach would have been more desirable. ~
Mitchell P. Dombrowski, MD, and Sidney E Bottoms, MD Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, WayneState University-HutzelHospital, 4707 St. Antoine Blvd., Detroit, M148201
REFERENCE 1. Godfrey KAM. Statistics in practice. N EnglJ Med 1985;313: 1450-6.
6/8/74296
Reply To the Editors: We read with interest the letter of Dombrowski and Bottoms. We appreciate the detail in which they analyzed our article, taking the time to recalculate the statistics. Indeed, the statistics reported in our study were odds ratios, inadvertently reported as relative risks. The Bonferroni method of correcting for multiple analyses is considered by many to be overly conservative; therefore we chose to report uncorrected p values to allow the reader to judge the significance for themselves. EUy M.-J. Xenakis, MD, Oded Lang~ MD, Jeanna M. Pip~ MD, Deborah Conway, MD, and Michael D. Berkus, MD Department of Obstetrics and Gynecology, University of Texas Health Center, 7703Floyd CurlDr., San Antonio, TX 78284-7836 6/8/74295
A "randomized" controlled trial without randomization To the Editors: The report by Xenakis et al. (Xenakis EM-J, Langer O, Piper JM, Conway D, Berkus MD. Low-dose versus high-dose oxytocin augmentation of labor A randomized controlled trial. A m J Obstet Gynecol 1995;173: 1874-8) misrepresents the research done. The title states that this was a randomized trial, yet the patients were not randomly allocated. The authors describe a sequential allocation by day of the week, which is not a random method)' 2 For example, patients enrolled on Mondays had a 100% probability of assignment to high-dose oxytocin rather than a 50% (or other fixed) probability, as would occur with random assignment.2 A more important problem with using day of the week for allocation is that it precluded concealment of the upcoming assignments. Recent research s has shown that failure to conceal the allocation sequence from those enrolling participants exaggerates the size of the treatm e n t effect by 30% to 40%, on average. Possible manifestations of these inadequacies in their allocation mechanism appear in their results. Because scheduled inductions of labor and elective cesarean births were apparently not included, roughly equal numbers of eligible patients each day of the week would be anticipated. Hence, with patients on 3 days of the week