William D. Fraser, MD, MSc Department of Obstetrics & Gynecology, Sherbrooke University Hospital Research Centre, Sherbrooke, Québec, Canada Gilles Paradis, MD, MSc Institut national de santé publique du Québec and, Department of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montréal, Québec, Canada Jessica Healy-Profitós, MPH University of Montreal Hospital Research Centre and Institut national de santé publique du Québec, Montréal, Québec, Canada Ada Hsieh Faculty of Medicine, McGill University, Montréal, Québec, Canada Marc-André Rhéaume, MD Department of Ophthalmology, University of Montreal, Montréal, Québec, Canada REFERENCES 1. Auger N, Fraser WD, Paradis G, Healy- Profitós J, Hsieh A, Rhéaume MA. Pre- eclampsia and long-term risk of maternal retinal disorders. Obstet Gynecol 2017; 129:42–9. 2. Auger N, Fraser W, Schnitzer M, Leduc L, Healy-Profitós J, Paradis G. Recurrent preeclampsia and subsequent cardiovas- cular risk. Heart 2017;103:235–43. 3. D’Amico DJ. Primary retinal retach- ment. N Engl J Med 2008;359:2346–54. 4. Gordis L. Epidemiology. 5th ed. Philadel- phia (PA): Elsevier/Saunders; 2014. 5. Kasza J, Wraith D, Lamb K, Wolfe R. Survival analysis of time-to-event data in respiratory health research studies. Re- spirology 2014;19:483–92. Attempted and Successful Vacuum-Assisted Vaginal Delivery by Prepregnancy Body Mass Index Ramos et al 1 have gone the extra mile to provide the encouraging evidence that, although obese women in need of operative delivery are less likely to receive vacuum assistance, there is no compromise in vacuum success rate if attempted. Clinicians’ concern for fail- ure or complications deters vacuum- assisted vaginal delivery attempts in obese women. Nevertheless, balancing the higher surgical risks and morbidity of cesarean delivery in advanced labor, clinicians may wish to consider at- tempting a vacuum extraction in clini- cally appropriate laboring women with obesity. Case selection is paramount. To assist decision on operative deliv- ery, intrapartum transperineal ultraso- nography is one tool that can be incorporated into clinical assessment. In nulliparous women, a progression angle of 120° or less, a downward or horizontal fetal head position, and a midline angle of 35° or greater on intrapartum trans- perineal ultrasonography predicts an 85% chance of difficult vacuum delivery requiring more than four pulls. 2 Impor- tantly, intrapartum transperineal ultraso- nography is better-tolerated by laboring women than conventional digital vaginal assessments. 3 Intrapartum transperineal ultrasonog- raphy has not been specifically applied to obese women requiring vacuum assis- tance. Nevertheless, this is certainly one direction worthy of pursuit in future research, not only to improve clinicians’ confidence in identifying the right case for successful operative delivery among obese women, but to enhance patient safety and advance the art of operative deliveries. Financial Disclosure: The authors did not report any potential conflicts of interest. Tsz-Kin Lo, MBBS, MRCOG Department of Obstetrics and Gynecology, Princess Margaret Hospital, Hong Kong SAR, China Wai-Lam Lau, MBBS, FRCOG Wing-Cheong Leung, MD, FRCOG Department of Obstetrics and Gynecology, Kwong Wah Hospital, Hong Kong SAR, China REFERENCES 1. Ramos SZ, Waring ME, Leung K, Amir NS, Bannon AL, Moore Simas TA. At- tempted and successful vacuum-assisted vaginal delivery by prepregnancy body mass index. Obstet Gynecol 2017;129: 311–320. 2. Sainz JA, Borrero C, Fernandez-Palacin A, Aquise A, Valdivieso P, Pastor L, et al. Intrapartum transperineal ultra- sound as a predictor of instrumenta- tion dif ficulty with vacuum-assisted delivery in primiparous women. J Matern Fetal Neonatal Med 2015; 28:2041–7. 3. Chan YT, Ng KS, Yung WK, Lo TK, Lau WL, Leung WC. Is intrapartum translabial ultrasound examination painless? J Matern Fetal Neonatal Med 2016;29:3276–80. Editor’s Note: Ramos et al declined to respond. 948 Letters OBSTETRICS & GYNECOLOGY Copyright ª by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.