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Fetal endoscopic surgery: Lessons learned and trends reviewed
Fetal Endoscopic Surgery: Lessons Learned and Trends Reviewed By Steven F. Fowler, Roman M. Sydorak, Craig T. Albanese, Diana L. Farmer, Michael R. Harrison, and Hanmin Lee San Francisco, California
Purpose: Fetal surgery is performed increasingly with minimal access approaches. The authors report their experience with fetal endoscopic procedures (fetendo) with emphasis on changing techniques and outcome trends.
changed from 10 mm to 5 mm. Chorioamniotic separation (31 of 66), premature rupture of membranes (32 of 66), chorioamnionitis (12 of 66), and fetal death (10 of 66) continued to be significant complications.
Methods: All fetal endoscopic cases performed at a single institution from January 1996 to August 2001 were reviewed (n ⫽ 66). Cases were examined with respect to year performed, type of operation, operative data, and outcome.
Conclusions: Fetal endoscopic surgery over the last 6 years has evolved toward shorter operating time, the use of smaller and fewer ports, decreased pump fluid exchange, and decreased blood loss, with the types of cases centered on twin-twin transfusion syndrome and congenital diaphragmatic hernia. J Pediatr Surg 37:1700-1702. Copyright 2002, Elsevier Science (USA). All rights reserved.
Results: Twin-twin transfusion syndrome (26 cases) and congenital diaphragmatic hernia (35 cases) were the most common diseases treated. From 1996 to 2001, there was a decrease in average operating time (256 to 127 minutes [P ⫽ .0006]), number of ports utilized (3.8 to one [P ⫽ .00001]), pump volume (28.7 to 2.7 L [P ⫽ .00001]), and estimated blood loss (408 to 29 mL [P ⫽ .008]). In addition, port size
F
ETAL SURGICAL INTERVENTION was first performed over 20 years ago.1 Surgery generally was reserved for life-threatening or severely debilitating anomalies because of concern for maternal safety. These operations involved a maternal laparotomy to expose the uterus followed by a hysterotomy for fetal exposure. Fetal morbidity, a significant complication of this intervention, was related directly to preterm labor and subsequent delivery.2 The use of endoscopic techniques in fetal surgery provided the theoretical possibility of decreasing morbidity by minimizing uterine trauma. As early as the 1970s, fetoscopy was shown to be safe for prenatal diagnosis.3 In an effort to decrease maternal as well as fetal morbidity, fetoscopic techniques have been used increasingly. MATERIALS AND METHODS
Our institution has performed fetal endoscopic surgery from 1996 until now. A retrospective chart review of patients undergoing fetal endoscopic surgery was conducted as well as an analysis of our fetal treatment database. Approval for this study was granted by our insti-
INDEX WORDS: Fetal surgery, fetendo, congenital diaphragmatic hernia, twin-twin transfusion syndrome.
tutional Committee for Human Research. Patient information was categorized with respect to year of operation and type of congenital anomaly. Operative characteristics consisting of time, estimated blood loss (EBL), size and number of ports utilized, and pump volume utilized. Postoperative complications of chorioamniotic separation (CAS), premature rupture of membranes (PROM), chorioamnionitis (CA), preterm labor (PTL), and mortality were reviewed. Statistical analysis was performed using a t test for continuous variables with a level of significance of P ⬍ .05. The pump device utilized for fetal endoscopic surgery was adapted at the University of California, San Francisco (Cobe Cardiovascular, Arvada, CO; Fig 1). It involves a reservoir of normal saline fluid passing to a pump head. Fluid then passes through a heater with a pressure monitoring device. Flow rate is adjusted using a bypass loop that connects back to the reservoir. Waste exchange is brought through a pump and delivered to a separate reservoir.
RESULTS
Sixty-six fetal endoscopic procedures were performed from 1996 to 2001. Twenty-six cases of twin-twin transfusion syndrome (TTTS) and 35 cases of congenital diaphragmatic hernia (CDH) were treated. CDH provided our first experience with fetal endoscopic surgery, Table 1. Fetal Cases by Year
From the Department of Surgery, Division of Pediatric Surgery and Fetal Treatment Center, University of California, San Francisco, CA. Presented at the 35th Annual Meeting of the Pacific Association of Pediatric Surgeons, La Jolla, California, May 12-16, 2002. Address reprint requests to Hanmin Lee, MD, HSW 1601, 513 Parnassus Ave, San Francisco, CA 94143-0570. Copyright 2002, Elsevier Science (USA). All rights reserved. 0022-3468/02/3712-0013$35.00/0 doi:10.1053/jpsu.2002.36699 1700
Year
TTTS
CDH
MMC
OU
CHAOS
1996 1997 1998 1999 2000 2001 Total
0 0 1 9 8 8 26
6 6 5 9 6 3 35
0 0 1 1 1 0 3
0 0 0 1 0 0 1
0 1 0 0 0 0 1
Journal of Pediatric Surgery, Vol 37, No 12 (December), 2002: pp 1700-1702
FETAL ENDOSURGERY
1701
Fig 1. The high-flow irrigating system consists of an extracorporeal pump and a heat exchanger that continuously circulates warmed lactated Ringer’s solution via a sheath through which the fetoscope is placed (inset).
and we have treated an average of 6 cases per year. Three cases of myelomeningocele (MMC) were treated from 1998 to 2000. One fetus with obstructive uropathy and one with tracheal atresia were treated endoscopically (Table 1). From 1996 to 2001, average operating time has decreased from 256 to 127 minutes (P ⫽ .0006). The number of ports has decreased from 3.8 to one (P ⫽ .00001). Port size used has changed from 10 mm to 5 mm. Pump volume has dropped from 28.7 to 2.7 L (P ⫽ .00001). Estimated blood loss has dropped from 408 to 29 mL (P ⫽ .008). CMS (31 of 66), PROM (32 of 66), CA (12 of 66), and fetal death (10 of 66) continue to be significant complications. There were no maternal fatalities (Table 2). TTTS has the shortest operating time, smallest pump volume, and least amount of blood loss. TTTS was responsible for 8 of 10 cases of fetal mortality among the patients. CDH had 25 cases of premature rupture of membranes, 19 progressed to preterm labor. Compared with TTTS, CDH had longer operating time, blood loss, and pump volume. Other cases of fetal endoscopic surgery comprising MMC, obstructive uropathy (OU), and congenital high airway obstructive syndrome (CHAOS) had significantly longer operating times, and blood loss (Table 3).
DISCUSSION
Fetal endoscopic (fetendo) surgery has been used for a relatively limited number of fetal anomalies. Fetal intervention with CDH currently is under investigation in a National Institute of Health sponsored trial. The trial is evaluating the efficacy of prenatal tracheal occlusion compared with standard postnatal care for severe cases of CDH. Tracheal occlusion has been shown to stimulate lung development and may be of benefit in severe cases of CDH with resultant pulmonary hypoplasia.4 The current technique of in utero treatment for CDH involves temporary tracheal occlusion with an endotracheal balloon.5 This technique can be performed through one 5-mm port and has evolved from prior tracheal clip occlusion, which required 3 ports. Severe TTTS has become the most common indication for fetoscopic intervention over the past 4 years at our institution. In 15% of twin monochorionic pregnancies there is a net flow of blood from one twin to the other resulting in TTTS. Mortality rates in severe cases when diagnosed in the midtrimester range from 80% to 100% without intervention. Interruption of this transfusion by eliminating the intertwin connections can increase outcome with reported survival rate of 50% to 70%.6 This procedure has advanced technically with the ability to
Table 2. Experience, by Year, With Fetoscopic Surgery Year
Cases
Operating Room time (Avg, min)
EBL (Avg, mL)
Pump Volume (Avg, L)
CAS
PROM
CA
PTL
Fetal Demise
1996 1997 1998 1999 2000 2001 Total
6 7 7 20 15 11 66
256 260 200 164 102 127 179
408 438 157 89 39 29 155
28.7 29.2 27.9 15.9 6 2.7 15.4
3 4 3 10 8 3 31
4 5 3 7 10 3 32
2 0 2 3 4 1 12
4 5 3 6 8 3 29
0 0 1 3 2 4 10
Abbreviations: Avg, average; EBL, estimated blood loss.
1702
FOWLER ET AL
Table 3. Experience, by Diagnosis, With Fetal Surgery Disease
Cases
Operating Room Time (Avg, min)
TTTS CDH MMC OU CHAOS
26 35 3 1 1
124 186 295 142 420
EBL (Avg, mL)
Pump Volume (Avg, L)
CAS
PROM
CA
PTL
Fetal Demise
30 198 200 100 1500
7.7 17.9 44 12 48
9 21 1 0 0
5 25 2 0 0
0 11 1 0 0
10 19 0 0 1
8 1 1 0 0
Abbreviations: Avg, average; EBL, estimated blood loss.
identify the intertwin connections by duplex ultrasound scan and fetoscopy. The procedure can be performed via one port with a minilaparotomy and with favorable placental anatomy can be performed percutaneously. Use of standard endoscopic instrumentation has been critical for the evolution of fetoscopic surgery, but modifications to laparoscopy have been necessary. Distension of the uterus can be achieved with CO2, but Grataco´ s et al7 showed severe acidosis in the ewe fetus during a fetoscopic procedure. Although fluid distension decreases visualization compared with gas, the benefits of maintaining a more physiologic environment for the fetus are critical. Severe insufflation should be avoided to prevent placento-uterine disruption. Additionally, intrauterine pressures below 20 mm Hg preserve placental blood flow and prevent fetal hypoxia.8 We have decreased our pump volume and hypothesize that the resultant decrease in turbulence may be less damaging to the fetal membranes. In addition, smaller and fewer ports likely minimize membrane trauma. In most instances, access to the uterus is gained via a small maternal laparotomy. Ultrasonography is used to guide placement of the port(s) in an area free of placenta. The uterus is traversed with a sharp trocar. Two- to 5-mm ports are used and 1- to 4-mm endoscopes are introduced through them. The most common fetendo complication is PROM. The likelihood of PROM is associated with the size and number of ports. Single ports have been reported to cause PROM in approximately 10% of cases, compared with
60% in multiport cases.5,9 Modifications in standard laparoscopic equipment have been designed to secure the membranes, but this still has not diminished this complication.10 Several techniques currently are being evaluated, but the issue of membrane disruption remains pivotal. For this reason, intervention with fetal endoscopic surgery only should be performed for life-threatening or severely debilitating anomalies with the potential for significant improvement with prenatal intervention. In our series, fetendo cases have undergone dramatic changes in terms of decreased operating time, smaller pump volume, and smaller and fewer ports. Operations for CDH have changed from 3 ports for tracheal clip application to one port for balloon placement. There has been an increase in the number of TTTS treatments involving one port for laser ablation. These advancements are caused by several factors including improvement in instrumentation and evolution of techniques. Laparoscopic instruments are thinner with the ability to roticulate for improved access. Endoscopes also have narrowed and improved in optics requiring less fluid exchange for optimal visualization. Ultrasound scan used in the operating room allows for improved orientation and positioning. As further advances are made in minimally invasive and imaging instrumentation, the scope of fetal intervention may continue to broaden. The Achilles heel of fetal intervention has been PTL, and this remains the most significant problem with minimal access fetal surgery.
REFERENCES 1. Harrison MR, Adzick NS, Longaker MT, et al: Successful repair in utero of a fetal diaphragmatic hernia after removal of herniated viscera from the left thorax. N Engl J Med 322:1582-1584, 1990 2. Harrison MR, Mychaliska GB, Albanese CT, et al: Correction of congenital diaphragmatic hernia in utero IX: Fetuses with poor prognosis (liver herniation and low lung-to-head ratio) can be saved by fetoscopic temporary tracheal occlusion. J Pediatr Surg 33:1017-1022, 1998 3. Rauskolb R: Fetoscopy—A new endoscopic approach. Endoscopy 2:107-113, 1979 4. DiFiore JW, Wilson JM: Lung development. Semin Pediatr Surg 3:221-232, 1994 5. Harrison MR, Albanese CT, Hawgood SB, et al: Fetoscopic temporary tracheal occlusion by means of detachable balloon for congenital diaphragmatic hernia. AJOG 158:730-733, 2001
6. Hecher K, Diehl W, Zikulnig L, et al: Endoscopic laser coagulation of placental anastamosis in 200 pregnancies with severe twintwin transfusion syndrome. Eur J Obstet Gynecol Reprod Biol 92:135139, 2000 7. Grataco´ s E, Wu J, Devlieger R, et al: Effects of amniodistension with carbon dioxide on fetal acid/base status during fetoscopic surgery in a sheep model. Surg Endosc 15:368-372, 2001 8. Skarsgard ED, Bealer JF, Meuli M, et al: Fetal endoscopic (Fetendo) surgery: The relationship between insufflating pressure and the fetoplacental circulation. J Pediatr Surg 30:1165-1168, 1995 9. Ville Y, Hecher K, Gagnon A, et al: Endoscopic laser coagulation in the management of severe twin transfusion syndrome. Br J Obstet Gynecol 105:446-453, 1998 10. Oberg KC, Robles AE, Ducsay CA, et al: Endoscopic intrauterine surgery in primates. Surg Endosc 13:420-426, 1999
Purpose: Fetal surgery is performed increasingly with minimal access approaches. The authors report their experience with fetal endoscopic procedures (fetendo) with emphasis on changing techniques and outcome trends.
changed from 10 mm to 5 mm. Chorioamniotic separation (31 of 66), premature rupture of membranes (32 of 66), chorioamnionitis (12 of 66), and fetal death (10 of 66) continued to be significant complications.
Methods: All fetal endoscopic cases performed at a single institution from January 1996 to August 2001 were reviewed (n ⫽ 66). Cases were examined with respect to year performed, type of operation, operative data, and outcome.
Conclusions: Fetal endoscopic surgery over the last 6 years has evolved toward shorter operating time, the use of smaller and fewer ports, decreased pump fluid exchange, and decreased blood loss, with the types of cases centered on twin-twin transfusion syndrome and congenital diaphragmatic hernia. J Pediatr Surg 37:1700-1702. Copyright 2002, Elsevier Science (USA). All rights reserved.
Results: Twin-twin transfusion syndrome (26 cases) and congenital diaphragmatic hernia (35 cases) were the most common diseases treated. From 1996 to 2001, there was a decrease in average operating time (256 to 127 minutes [P ⫽ .0006]), number of ports utilized (3.8 to one [P ⫽ .00001]), pump volume (28.7 to 2.7 L [P ⫽ .00001]), and estimated blood loss (408 to 29 mL [P ⫽ .008]). In addition, port size
F
ETAL SURGICAL INTERVENTION was first performed over 20 years ago.1 Surgery generally was reserved for life-threatening or severely debilitating anomalies because of concern for maternal safety. These operations involved a maternal laparotomy to expose the uterus followed by a hysterotomy for fetal exposure. Fetal morbidity, a significant complication of this intervention, was related directly to preterm labor and subsequent delivery.2 The use of endoscopic techniques in fetal surgery provided the theoretical possibility of decreasing morbidity by minimizing uterine trauma. As early as the 1970s, fetoscopy was shown to be safe for prenatal diagnosis.3 In an effort to decrease maternal as well as fetal morbidity, fetoscopic techniques have been used increasingly. MATERIALS AND METHODS
Our institution has performed fetal endoscopic surgery from 1996 until now. A retrospective chart review of patients undergoing fetal endoscopic surgery was conducted as well as an analysis of our fetal treatment database. Approval for this study was granted by our insti-
INDEX WORDS: Fetal surgery, fetendo, congenital diaphragmatic hernia, twin-twin transfusion syndrome.
tutional Committee for Human Research. Patient information was categorized with respect to year of operation and type of congenital anomaly. Operative characteristics consisting of time, estimated blood loss (EBL), size and number of ports utilized, and pump volume utilized. Postoperative complications of chorioamniotic separation (CAS), premature rupture of membranes (PROM), chorioamnionitis (CA), preterm labor (PTL), and mortality were reviewed. Statistical analysis was performed using a t test for continuous variables with a level of significance of P ⬍ .05. The pump device utilized for fetal endoscopic surgery was adapted at the University of California, San Francisco (Cobe Cardiovascular, Arvada, CO; Fig 1). It involves a reservoir of normal saline fluid passing to a pump head. Fluid then passes through a heater with a pressure monitoring device. Flow rate is adjusted using a bypass loop that connects back to the reservoir. Waste exchange is brought through a pump and delivered to a separate reservoir.
RESULTS
Sixty-six fetal endoscopic procedures were performed from 1996 to 2001. Twenty-six cases of twin-twin transfusion syndrome (TTTS) and 35 cases of congenital diaphragmatic hernia (CDH) were treated. CDH provided our first experience with fetal endoscopic surgery, Table 1. Fetal Cases by Year
From the Department of Surgery, Division of Pediatric Surgery and Fetal Treatment Center, University of California, San Francisco, CA. Presented at the 35th Annual Meeting of the Pacific Association of Pediatric Surgeons, La Jolla, California, May 12-16, 2002. Address reprint requests to Hanmin Lee, MD, HSW 1601, 513 Parnassus Ave, San Francisco, CA 94143-0570. Copyright 2002, Elsevier Science (USA). All rights reserved. 0022-3468/02/3712-0013$35.00/0 doi:10.1053/jpsu.2002.36699 1700
Year
TTTS
CDH
MMC
OU
CHAOS
1996 1997 1998 1999 2000 2001 Total
0 0 1 9 8 8 26
6 6 5 9 6 3 35
0 0 1 1 1 0 3
0 0 0 1 0 0 1
0 1 0 0 0 0 1
Journal of Pediatric Surgery, Vol 37, No 12 (December), 2002: pp 1700-1702
FETAL ENDOSURGERY
1701
Fig 1. The high-flow irrigating system consists of an extracorporeal pump and a heat exchanger that continuously circulates warmed lactated Ringer’s solution via a sheath through which the fetoscope is placed (inset).
and we have treated an average of 6 cases per year. Three cases of myelomeningocele (MMC) were treated from 1998 to 2000. One fetus with obstructive uropathy and one with tracheal atresia were treated endoscopically (Table 1). From 1996 to 2001, average operating time has decreased from 256 to 127 minutes (P ⫽ .0006). The number of ports has decreased from 3.8 to one (P ⫽ .00001). Port size used has changed from 10 mm to 5 mm. Pump volume has dropped from 28.7 to 2.7 L (P ⫽ .00001). Estimated blood loss has dropped from 408 to 29 mL (P ⫽ .008). CMS (31 of 66), PROM (32 of 66), CA (12 of 66), and fetal death (10 of 66) continue to be significant complications. There were no maternal fatalities (Table 2). TTTS has the shortest operating time, smallest pump volume, and least amount of blood loss. TTTS was responsible for 8 of 10 cases of fetal mortality among the patients. CDH had 25 cases of premature rupture of membranes, 19 progressed to preterm labor. Compared with TTTS, CDH had longer operating time, blood loss, and pump volume. Other cases of fetal endoscopic surgery comprising MMC, obstructive uropathy (OU), and congenital high airway obstructive syndrome (CHAOS) had significantly longer operating times, and blood loss (Table 3).
DISCUSSION
Fetal endoscopic (fetendo) surgery has been used for a relatively limited number of fetal anomalies. Fetal intervention with CDH currently is under investigation in a National Institute of Health sponsored trial. The trial is evaluating the efficacy of prenatal tracheal occlusion compared with standard postnatal care for severe cases of CDH. Tracheal occlusion has been shown to stimulate lung development and may be of benefit in severe cases of CDH with resultant pulmonary hypoplasia.4 The current technique of in utero treatment for CDH involves temporary tracheal occlusion with an endotracheal balloon.5 This technique can be performed through one 5-mm port and has evolved from prior tracheal clip occlusion, which required 3 ports. Severe TTTS has become the most common indication for fetoscopic intervention over the past 4 years at our institution. In 15% of twin monochorionic pregnancies there is a net flow of blood from one twin to the other resulting in TTTS. Mortality rates in severe cases when diagnosed in the midtrimester range from 80% to 100% without intervention. Interruption of this transfusion by eliminating the intertwin connections can increase outcome with reported survival rate of 50% to 70%.6 This procedure has advanced technically with the ability to
Table 2. Experience, by Year, With Fetoscopic Surgery Year
Cases
Operating Room time (Avg, min)
EBL (Avg, mL)
Pump Volume (Avg, L)
CAS
PROM
CA
PTL
Fetal Demise
1996 1997 1998 1999 2000 2001 Total
6 7 7 20 15 11 66
256 260 200 164 102 127 179
408 438 157 89 39 29 155
28.7 29.2 27.9 15.9 6 2.7 15.4
3 4 3 10 8 3 31
4 5 3 7 10 3 32
2 0 2 3 4 1 12
4 5 3 6 8 3 29
0 0 1 3 2 4 10
Abbreviations: Avg, average; EBL, estimated blood loss.
1702
FOWLER ET AL
Table 3. Experience, by Diagnosis, With Fetal Surgery Disease
Cases
Operating Room Time (Avg, min)
TTTS CDH MMC OU CHAOS
26 35 3 1 1
124 186 295 142 420
EBL (Avg, mL)
Pump Volume (Avg, L)
CAS
PROM
CA
PTL
Fetal Demise
30 198 200 100 1500
7.7 17.9 44 12 48
9 21 1 0 0
5 25 2 0 0
0 11 1 0 0
10 19 0 0 1
8 1 1 0 0
Abbreviations: Avg, average; EBL, estimated blood loss.
identify the intertwin connections by duplex ultrasound scan and fetoscopy. The procedure can be performed via one port with a minilaparotomy and with favorable placental anatomy can be performed percutaneously. Use of standard endoscopic instrumentation has been critical for the evolution of fetoscopic surgery, but modifications to laparoscopy have been necessary. Distension of the uterus can be achieved with CO2, but Grataco´ s et al7 showed severe acidosis in the ewe fetus during a fetoscopic procedure. Although fluid distension decreases visualization compared with gas, the benefits of maintaining a more physiologic environment for the fetus are critical. Severe insufflation should be avoided to prevent placento-uterine disruption. Additionally, intrauterine pressures below 20 mm Hg preserve placental blood flow and prevent fetal hypoxia.8 We have decreased our pump volume and hypothesize that the resultant decrease in turbulence may be less damaging to the fetal membranes. In addition, smaller and fewer ports likely minimize membrane trauma. In most instances, access to the uterus is gained via a small maternal laparotomy. Ultrasonography is used to guide placement of the port(s) in an area free of placenta. The uterus is traversed with a sharp trocar. Two- to 5-mm ports are used and 1- to 4-mm endoscopes are introduced through them. The most common fetendo complication is PROM. The likelihood of PROM is associated with the size and number of ports. Single ports have been reported to cause PROM in approximately 10% of cases, compared with
60% in multiport cases.5,9 Modifications in standard laparoscopic equipment have been designed to secure the membranes, but this still has not diminished this complication.10 Several techniques currently are being evaluated, but the issue of membrane disruption remains pivotal. For this reason, intervention with fetal endoscopic surgery only should be performed for life-threatening or severely debilitating anomalies with the potential for significant improvement with prenatal intervention. In our series, fetendo cases have undergone dramatic changes in terms of decreased operating time, smaller pump volume, and smaller and fewer ports. Operations for CDH have changed from 3 ports for tracheal clip application to one port for balloon placement. There has been an increase in the number of TTTS treatments involving one port for laser ablation. These advancements are caused by several factors including improvement in instrumentation and evolution of techniques. Laparoscopic instruments are thinner with the ability to roticulate for improved access. Endoscopes also have narrowed and improved in optics requiring less fluid exchange for optimal visualization. Ultrasound scan used in the operating room allows for improved orientation and positioning. As further advances are made in minimally invasive and imaging instrumentation, the scope of fetal intervention may continue to broaden. The Achilles heel of fetal intervention has been PTL, and this remains the most significant problem with minimal access fetal surgery.
REFERENCES 1. Harrison MR, Adzick NS, Longaker MT, et al: Successful repair in utero of a fetal diaphragmatic hernia after removal of herniated viscera from the left thorax. N Engl J Med 322:1582-1584, 1990 2. Harrison MR, Mychaliska GB, Albanese CT, et al: Correction of congenital diaphragmatic hernia in utero IX: Fetuses with poor prognosis (liver herniation and low lung-to-head ratio) can be saved by fetoscopic temporary tracheal occlusion. J Pediatr Surg 33:1017-1022, 1998 3. Rauskolb R: Fetoscopy—A new endoscopic approach. Endoscopy 2:107-113, 1979 4. DiFiore JW, Wilson JM: Lung development. Semin Pediatr Surg 3:221-232, 1994 5. Harrison MR, Albanese CT, Hawgood SB, et al: Fetoscopic temporary tracheal occlusion by means of detachable balloon for congenital diaphragmatic hernia. AJOG 158:730-733, 2001
6. Hecher K, Diehl W, Zikulnig L, et al: Endoscopic laser coagulation of placental anastamosis in 200 pregnancies with severe twintwin transfusion syndrome. Eur J Obstet Gynecol Reprod Biol 92:135139, 2000 7. Grataco´ s E, Wu J, Devlieger R, et al: Effects of amniodistension with carbon dioxide on fetal acid/base status during fetoscopic surgery in a sheep model. Surg Endosc 15:368-372, 2001 8. Skarsgard ED, Bealer JF, Meuli M, et al: Fetal endoscopic (Fetendo) surgery: The relationship between insufflating pressure and the fetoplacental circulation. J Pediatr Surg 30:1165-1168, 1995 9. Ville Y, Hecher K, Gagnon A, et al: Endoscopic laser coagulation in the management of severe twin transfusion syndrome. Br J Obstet Gynecol 105:446-453, 1998 10. Oberg KC, Robles AE, Ducsay CA, et al: Endoscopic intrauterine surgery in primates. Surg Endosc 13:420-426, 1999