- Email: [email protected]
Growth discordance in twins
Letters 897
Volume 189, Number 3 Am J Obstet Gynecol
methods and found similar results.3 We therefore feel confident that the method used in this protocol is a reliable one. In response to the concern regarding the units presented, our units, while not the more commonly used ones, are nevertheless acceptable and in our opinion more representative of the concept of HRV because the units more closely follow the variation in heart rate.2 We did not present data on the low-frequency (LF)/ high-frequency ratio because the very significance of LF as a measure of sympathetic activity is not entirely clear. The LF component of HRV corresponds to blood pressure oscillations occurring around 0.1 Hz and is jointly modulated by the sympathetic and parasympathetic nervous systems. We therefore presented contractility indices as a true reflection of cardiac sympathetic nervous system drive.3 Finally, indeed our study may be the only study to date in the literature supporting a favorable effect of combination hormone therapy on autonomic cardiovascular modulation. However, other studies have documented an increase in parasympathetic activity during the leutinizing phase of the menstrual cycle, which provides further evidence of an effect of progesterone on autonomic function. Noha H. Farag, MD, Richard A. Nelesen, PhD, and Paul J. Mills, PhD Department of Psychiatry, University of California, San Diego, UCSD Medical Center, 200 W Arbor Dr, CTF-A415, San Diego, CA 921030804; e-mail: [email protected]
REFERENCES 1. Burleson MH, Malarkey WB, Cacioppo JT, Poehlmann KM, KiecoltGlaser JK, Berntson GG, et al. Postmenopausal hormone replacement: effects on autonomic, neuroendocrine, and immune reactivity to brief psychological stressors. Psychosom Med 1998;60:17-25. 2. Nagel JH, Han K, Hurwitz BE, Schneiderman N. Assessment and diagnostic applications of heart rate variability. Biomed Eng Appl Basis Comm 1993;5:147-58. 3. Nelesen RA, Yu H, Ziegler MG, Mills PJ, Clausen JL, Dimsdale JE. Continuous positive airway pressure normalizes cardiac autonomic and hemodynamic responses to a laboratory stressor in apneic patients. Chest 2001;119:1092-101.
sample of 173 twin pregnancies, although chorionicity could be determined for only 136 pregnancies. Furthermore, only 19 pregnancies were found to be monochorionic. Thus, of the analyzed cases, only 11% represented known monochorionic pregnancies. Previous studies2 have demonstrated that monochorionic twins have nearly a 3-fold incidence of adverse outcomes (eg, death, cerebral palsy, mental retardation) compared with dichorionic twins. The low percentage and absolute number of monochorionic pregnancies would predict a lack of impact of this subgroup on the logistic regression model as described by the authors. Consequently, one should not use these data to assess the impact of growth discordance among monochorionic twins. An additional issue concerns the use of birth weight measurements in this retrospective study. It would be of value to review the estimated discordance on the basis of ultrasonographic examinations performed before delivery in this population and the correlation with actual birth weight discordance. In view of the established variance in prenatal ultrasound weight assessments, a birth weight-based threshold level (30% discordance) may be far too stringent to be applied during antenatal care. Furthermore, the authors note that the 30% discordance is associated with a significantly increased incidence of adverse outcome. Certainly, interventions should occur before a threshold level associated with adverse outcome is reached, while appropriately weighing maternal and fetal risks. In view of the markedly increased risks associated with monochorionic pregnancy and the risk of twin-twin transfusion, we recommend adherence to American College of Obstetricians and Gynecologists Educational Bulletin No. 253,3 which recommends frequent antenatal fetal surveillance and consideration of early delivery for discordance of 20%. Michael G. Ross, MD, MPH Department of Obstetrics and Gynecology, Box 3, Harbor-UCLA Medical Center, 1000 W Carson St, Torrance, CA 90509-2910; e-mail: [email protected]
Martin van Gemert, PhD Lasercentrum, Academisch Medisch Centrum, Meibergdreef 9, 1105 AZ Amsterdam Zuidosst, The Netherlands
doi:10.1067/S0002-9378(03)00632-X REFERENCES
Growth discordance in twins To the Editors: We read with interest the article by Redman et al1 in which the authors indicate that defining pathologic discordance as the 95th percentile or >30% difference enhances its predictive value. Despite the interesting analysis, there are significant concerns with this conclusion in regard to monochorionic versus dichorionic twins. The pathophysiologic mechanisms of growth discordance may differ between monochorionic versus dichorionic twins. Although dichorionic twins may demonstrate discordance as a result of placental location, constitutive genetic issues, and/or selective intrauterine events, monochorionic twins have the added risks of twin-twin transfusion syndrome and unequal placental sharing. In the current study, the authors report an initial
1. Redman ME, Blackwell SC, Refuerzo JS, Kruger M, Naccasha N, Hassan SS, et al. The ninety-fifth percentile for growth discordance predicts complications of twin pregnancy. Am J Obstet Gynecol 2002;187:667-71. 2. Minakami H, Honma Y, Matsubara S, Uchida A, Shiraishi H, Sato I. Effects of placental chorionicity on outcome in twin pregnancies: a cohort study. J Reprod Med 1999;44:595-600. 3. American College of Obstetricians and Gynecologists. Special problems of multiple gestation. Washington (DC): The College; 1998. Educational bulletin No.: 253.
doi:10.1067/S0002-9378(03)00625-2
Reply To the Editors: We sincerely thank Drs Ross and van Gemert for their interest in our article. We believe that their
Volume 189, Number 3 Am J Obstet Gynecol
methods and found similar results.3 We therefore feel confident that the method used in this protocol is a reliable one. In response to the concern regarding the units presented, our units, while not the more commonly used ones, are nevertheless acceptable and in our opinion more representative of the concept of HRV because the units more closely follow the variation in heart rate.2 We did not present data on the low-frequency (LF)/ high-frequency ratio because the very significance of LF as a measure of sympathetic activity is not entirely clear. The LF component of HRV corresponds to blood pressure oscillations occurring around 0.1 Hz and is jointly modulated by the sympathetic and parasympathetic nervous systems. We therefore presented contractility indices as a true reflection of cardiac sympathetic nervous system drive.3 Finally, indeed our study may be the only study to date in the literature supporting a favorable effect of combination hormone therapy on autonomic cardiovascular modulation. However, other studies have documented an increase in parasympathetic activity during the leutinizing phase of the menstrual cycle, which provides further evidence of an effect of progesterone on autonomic function. Noha H. Farag, MD, Richard A. Nelesen, PhD, and Paul J. Mills, PhD Department of Psychiatry, University of California, San Diego, UCSD Medical Center, 200 W Arbor Dr, CTF-A415, San Diego, CA 921030804; e-mail: [email protected]
REFERENCES 1. Burleson MH, Malarkey WB, Cacioppo JT, Poehlmann KM, KiecoltGlaser JK, Berntson GG, et al. Postmenopausal hormone replacement: effects on autonomic, neuroendocrine, and immune reactivity to brief psychological stressors. Psychosom Med 1998;60:17-25. 2. Nagel JH, Han K, Hurwitz BE, Schneiderman N. Assessment and diagnostic applications of heart rate variability. Biomed Eng Appl Basis Comm 1993;5:147-58. 3. Nelesen RA, Yu H, Ziegler MG, Mills PJ, Clausen JL, Dimsdale JE. Continuous positive airway pressure normalizes cardiac autonomic and hemodynamic responses to a laboratory stressor in apneic patients. Chest 2001;119:1092-101.
sample of 173 twin pregnancies, although chorionicity could be determined for only 136 pregnancies. Furthermore, only 19 pregnancies were found to be monochorionic. Thus, of the analyzed cases, only 11% represented known monochorionic pregnancies. Previous studies2 have demonstrated that monochorionic twins have nearly a 3-fold incidence of adverse outcomes (eg, death, cerebral palsy, mental retardation) compared with dichorionic twins. The low percentage and absolute number of monochorionic pregnancies would predict a lack of impact of this subgroup on the logistic regression model as described by the authors. Consequently, one should not use these data to assess the impact of growth discordance among monochorionic twins. An additional issue concerns the use of birth weight measurements in this retrospective study. It would be of value to review the estimated discordance on the basis of ultrasonographic examinations performed before delivery in this population and the correlation with actual birth weight discordance. In view of the established variance in prenatal ultrasound weight assessments, a birth weight-based threshold level (30% discordance) may be far too stringent to be applied during antenatal care. Furthermore, the authors note that the 30% discordance is associated with a significantly increased incidence of adverse outcome. Certainly, interventions should occur before a threshold level associated with adverse outcome is reached, while appropriately weighing maternal and fetal risks. In view of the markedly increased risks associated with monochorionic pregnancy and the risk of twin-twin transfusion, we recommend adherence to American College of Obstetricians and Gynecologists Educational Bulletin No. 253,3 which recommends frequent antenatal fetal surveillance and consideration of early delivery for discordance of 20%. Michael G. Ross, MD, MPH Department of Obstetrics and Gynecology, Box 3, Harbor-UCLA Medical Center, 1000 W Carson St, Torrance, CA 90509-2910; e-mail: [email protected]
Martin van Gemert, PhD Lasercentrum, Academisch Medisch Centrum, Meibergdreef 9, 1105 AZ Amsterdam Zuidosst, The Netherlands
doi:10.1067/S0002-9378(03)00632-X REFERENCES
Growth discordance in twins To the Editors: We read with interest the article by Redman et al1 in which the authors indicate that defining pathologic discordance as the 95th percentile or >30% difference enhances its predictive value. Despite the interesting analysis, there are significant concerns with this conclusion in regard to monochorionic versus dichorionic twins. The pathophysiologic mechanisms of growth discordance may differ between monochorionic versus dichorionic twins. Although dichorionic twins may demonstrate discordance as a result of placental location, constitutive genetic issues, and/or selective intrauterine events, monochorionic twins have the added risks of twin-twin transfusion syndrome and unequal placental sharing. In the current study, the authors report an initial
1. Redman ME, Blackwell SC, Refuerzo JS, Kruger M, Naccasha N, Hassan SS, et al. The ninety-fifth percentile for growth discordance predicts complications of twin pregnancy. Am J Obstet Gynecol 2002;187:667-71. 2. Minakami H, Honma Y, Matsubara S, Uchida A, Shiraishi H, Sato I. Effects of placental chorionicity on outcome in twin pregnancies: a cohort study. J Reprod Med 1999;44:595-600. 3. American College of Obstetricians and Gynecologists. Special problems of multiple gestation. Washington (DC): The College; 1998. Educational bulletin No.: 253.
doi:10.1067/S0002-9378(03)00625-2
Reply To the Editors: We sincerely thank Drs Ross and van Gemert for their interest in our article. We believe that their