- Email: [email protected]
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy
International Journal of Gynecology and Obstetrics (2008) 100, 56–59
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / i j g o
CLINICAL ARTICLE
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy A. Sau a,⁎, M. Weber b , A.H. Shennan c , D. Maxwell d a
Department of Obstetrics and Gynaecology, University Hospital Lewisham, London, UK Paediatric Pathology, Great Ormond Street Hospital for Children, London, UK c King's College London, Guy's Kings and St Thomas' School of Medicine, Maternal and Fetal Research Unit, St Thomas' Hospital, London, UK d Fetal Medicine Unit, St Thomas' Hospital, London, UK b
Received 27 April 2007; received in revised form 15 June 2007; accepted 21 June 2007
KEYWORDS Arteriovenous anastomoses (AVA); Monochorionic twins; Twin-to-twin transfusion syndrome (TTTS); Antenatal detection
Abstract Objectives: To revalidate the detection technique for arteriovenous anastomoses in an unselected group of monochorionic twins, and to make recommendations about its applicability for more widespread use. Methods: Women with monochorionic diamniotic (MCDA) twins were recruited and underwent placental mapping by color Doppler ultrasound. Images of placental maps showing the location and type of anastomoses were saved as digital video clips. After delivery, dye injection study of all the placentas was performed to delineate the site and type of anastomoses. A digital photograph of each injection study was taken and saved. The antenatal ultrasound images and postnatal dye injection studies were compared. Results: 18 sets MCDA twins were evaluated. In 3 cases there was evidence of twin-to-twin transfusion syndrome. Dye injection of 18 placentas revealed 21 arterio-arterial anastomoses (AAA), 21 arteriovenous anastomoses (AVA) and 4 veno-venous anastomoses (VVA). Of these, 10 (48%) AAAs and 5 (24%) AVAs were detected antenatally by color Doppler. In all cases, where an AVA was detected, the placenta was located anteriorly. Conclusion: Antenatal detection of AVA was feasible when the placenta was located anteriorly, but proved difficult in posteriorly situated placentas. © 2007 Published by Elsevier Ireland Ltd. on behalf of International Federation of Gynecology and Obstetrics.
1. Introduction Twin-to-twin transfusion syndrome (TTTS) is the most serious complication of monochorionic twins, affecting about 10%–20% ⁎ Corresponding author. Tel.: +44 02083333000x6214; fax: +44 02086901963. E-mail addresses: [email protected], [email protected] (A. Sau).
of all such twin pregnancies, and with a mortality rate of 80% if untreated [1,2]. Arteriovenous anastomoses (AVA) are a common form of inter-twin vascular connection and are implicated as a causative mechanism in the development of TTTS [3,4] by mediating unbalanced inter-twin transfusion from donor to recipient. Selective laser ablation of AVAs therefore addresses the underlying pathophysiological basis of the disease. Of all the available treatment modalities, it is associated with highest survival rate [5]. However, some
0020-7292/$ - see front matter © 2007 Published by Elsevier Ireland Ltd. on behalf of International Federation of Gynecology and Obstetrics. doi:10.1016/j.ijgo.2007.06.043
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy fetal medicine specialists feel that the initial fetoscopic identification of these anastomoses may prolong the procedure, thereby increasing the risk of spontaneous rupture of membrane. Consequently, antenatal mapping of the vascular equator by color and spectral Doppler might be helpful in reducing the duration of the procedure. Two preliminary reports involving 7 pairs of highly selective monochorionic twins have shown that specific arteriovenous anastomoses can be visualized by using specialized color Doppler ultrasound techniques [6,7]. If this technique could be replicated reliably and then found capable of incorporation into clinical practice, a considerable advance in the management of twin pregnancies would have been achieved. The aims of our study were to revalidate the clinical efficacy of the color Doppler technique, to perform the evaluations in a larger group of unselected monochorionic twin pregnancies, and to make recommendations about its applicability for more widespread twin surveillance.
2. Materials and methods This study was conducted from September 2002 to December 2003. Pregnant women were recruited from the Twin Ultrasound Surveillance Clinic after confirmation of monochorionic placentation. These patients were normally seen in this clinic fortnightly or more often, as clinically indicated. In addition to the standard ultrasound examination routinely performed on these patients, those recruited had undergone color Doppler examination of the fetal surface of the placenta to try to identify anastomosing vessels using high resolution, real time sonographic equipment (5–8 MHz Elegra; Siemens, Stockton, CA, USA). This study was approved by the Guy's and St Thomas' Research Ethics Committee. Placental mapping was performed using the technique described by Machin et al. [7]. The technique involves the standard location of the placental cord insertion sites using greyscale and color Doppler techniques. The placental tissue situated between the two cord insertion sites was then interrogated using color Doppler to identify an unaccompanied unpaired vascular structure on the fetal surface of the placenta. Once identified the cursor gate was placed within this vascular structure to demonstrate arterial flow in one segment and venous flow in the other segment
Figure 1 Dye injection of the placenta showing the site of arteriovenous anastomosis (yellow arrow).
57
of the vessel. The flow direction was similar in both arterial and venous portions. Images of placental maps showing the location and type of anastomoses were saved as digital video clips. All women were scanned by one sonographer (AS). After delivery, all placentas were examined by a perinatal pathologist. Macroscopic identification of anastomoses was recorded in the notes before injection of dye into the placental vessels using the method of Denbow et al. [8]. Digital photographs of each injection study were taken and saved (Fig. 1). Comparison of the antenatal ultrasound images regarding type and location of anastomoses and postnatal dye injection studies were performed. Perinatal outcome of all monochorionic diamniotic (MCDA) twins were recorded.
3. Results During the study period 30 women attended the twin surveillance clinic, of which 20 agreed to participate in the study. In 2 cases, although antenatal placental mapping was performed, postnatal dye injection was not possible because of delay in examining the placenta. Both antenatal and postnatal examinations were completed in 18 cases. In 3 cases there was evidence of twin-to-twin transfusion syndrome (Table 1). Case 4 went into premature labor the day after amnioreduction of 1.5 L; case 6 was delivered by elective cesarean delivery after 3 amnioreductions; and case 9 was delivered without any antenatal intervention. The placental locations were anterior in 10 cases, posterior in 7 cases, and fundal in 1 case. Four women were obese with body mass index (BMI) of N 30. As shown in Table 1 it was possible to detect arteriovenous anastomoses (AVA) on only 5 occasions. In 4 cases it was detected between 20 and 26 weeks of gestation, and in another case it was detected at 28 weeks. Dye injection of 18 placentas revealed 21 arterio-arterial anastomoses (AAA), 21 arteriovenous anastomoses (AVA), and 4 veno-venous anastomoses (VVA). Of these, 48% AAAs and 24% AVAs were detected antenatally by color Doppler. In all cases, where AVA was detected, the placenta was located anteriorly.
4. Discussion Identification of arteriovenous anastomoses by non-invasive Doppler ultrasound technique may prove highly valuable in the obstetric management of MCDA twins. This information has been used in the planning and performance of fetoscopic laser coagulation with successful outcomes [9,10]. Furthermore, Doppler could direct non-invasive treatment such as interstitial laser or focused ultrasound therapy for the occlusion of arteriovenous anastomoses [11,12]. This technique can be seen to have two potential clinical applications: a primary role in identifying pregnancies at risk of TTTS, and a secondary role in facilitating treatment if TTTS develops. Unfortunately, the technique has technical constraints: obese patients, posterior placentas, and earlier gestation when the vessels are still quite small. The present series used the techniques of Machin et al. [9]. It was possible to detect the AVAs on only 24% of occasions despite rigorous scanning attempts. The low detection rate in this series may reflect an unselected population. Posteriorly situated placentas (7 of 18 cases) and maternal obesity (BMIN 30 in 4 cases) was thought to contribute to the failure rate. In majority
58 Table 1
A. Sau et al. Comparison of antenatal detection and postnatal dye injection of anastomotic vessels in MCDA twins
Case
Diagnosis
Placenta location
Gestation at placental mapping (weeks)
Detection of anastomoses by ultrasound
Gestation at delivery (weeks)
Mode of delivery
Birth weight (g)
Detection of anastomoses by dye injection
1
MCDA
Posterior
22
Nil
38
SVD
2760 2540
2
MCDA
Anterior
24
1 AAA 1 AVA
38+ 4
Em LSCS
2390 3240
3
MCDA
Posterior
26
1 AAA
38
4
MCDA TTTS MCDA
Anterior
26
1 AVA
26+ 3
El LSCS SVD
Anterior
28
2 AAA
38
Anterior
28
1 AVA
32
7
MCDA TTTS MCDA
Anterior
24
Nil
38
Em LSCS El LSCS Em LSCS
8
MCDA
Anterior
20
Nil
36
SVD
9
Posterior
22
Nil
29+ 5
10
MCDA TTTS MCDA
Posterior
24
Nil
38
Em LSCS SVD
11
MCDA
Posterior
22
Nil
38
12
MCDA
Anterior
28
1 AAA
38
13
MCDA
Fundal
24
1 AAA
38+ 5
14
MCDA
Anterior
22
1 AAA 1 AVA
38
2640 2370 840 460 2860 2630 1255 1980 3200 2800 2500 1900 1008 1590 2550 2660 2082 2087 2530 2520 2500 1920 1720 1753
1 AAA 1 AVA 1 VVA 2 AVA (T1–T2) 3 AVA (T2–T1) 1 AAA 1 AVA (T1–T2) 1 AVA (T2–T1) 2 AAA 1 AVA 2 AAA 1VVA 1 AVA
15
MCDA
Anterior
20
1 AVA
34
Em LSCS
1540 2360
16
MCDA
Posterior
22
1 AAA
34
17
MCDA
Posterior
24
Nil
36
Em LSCS SVD
18
MCDA
Anterior
20
2 AAA
38
SVD
1940 1639 2200 2100 2350 2670
5 6
El LSCS Em LSCS Em LSCS SVD
1VVA 1 AAA 1 AVA 2 AAA 2 AVA 1 AAA 1 AAA 1 AVA 1 AAA 1 AVA (T1–T2) 2 AVA (T2–T1) 1 AAA 1 VVA 2 AVA (T1–T2) 1 AVA (T2–T1) 1 AAA 2 AAA 2 AAA 1 AVA 3 AAA
Abbreviations: TTTS, twin-to-twin n transfusion syndrome; AAA, arterio-arterial anastomoses; AVA, arteriovenous anastomoses, VVA, venovenous anastomoses; Em, emergency; El, Elective; LSCS, lower segment cesarean delivery; SVD, spontaneous vaginal delivery; T1–T2, twin 1 to twin 2; T2–T1, twin 2 to twin 1; MCDA, monochorionic diamniotic.
of the cases, detection of anastomoses was made at or after 20 weeks, and this may be due to smaller vessel size at earlier gestation. In our opinion, attempts to detect AVA should be made from 18 weeks of gestation. With advances in ultrasound technology, such as the use of high definition ultrasound with 4D technology and dynamic magnetic resonance imaging, the detection rate is likely to improve. From this study it can be concluded that antenatal detection of arteriovenous anastomoses was feasible, and the technique reproducible. However, further work to reduce
or eradicate the technical constraints and reduce the failure rate are necessary before this technique can be recommended for routine clinical application.
References [1] De Lia JE, Kuhlmann RS, Harstad TW, Cruikshank DP. Fetoscopic laser ablation of placental vessels in severe previable twin-twin transfusion. Am J Obstet Gynecol 1995;172:1202–8.
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy [2] Fisk NM, Taylor MJO. The fetus(es) with twin twin transfusion syndrome. In: Harrison M, Evans M, Adzick S, Holzgreve W, editors. The unborn patient: the art and science of fetal therapy. Philadelphia: W.B. Saunders Company; 2000. [3] Machin G, Still K, Lalani T. Correlations of placental vascular anatomy and clinical outcomes in 69 monochorionic twin pregnancies. Am J Med Genet 1996;61:229–36. [4] Bajoria R, Wigglesworth J, Fisk N. Angioarchitecture of monochorionic placentas in relation to the twin-twin transfusion syndrome. Am J Obstet Gynecol 1995;172:856–63. [5] Quintero RA, Morales WJ, Mendoza G, Allen M, Kalter CS, Giannina G, et al. Selective photocoagulation of placental vessels in twin-twin transfusion syndrome: evolution of a surgical technique. Obstet Gynecol Surv 1998;53:S97–S103. [6] Taylor MJ, Farquharson D, Cox PM, Fisk NM. Identification of arterio-venous anastomoses in vivo in monochorionic twin pregnancies: preliminary report. Ultrasound Obstet Gynecol 2000;16:218–22. [7] Machin GA, Feldstein VA, van Gemert MJ, Keith LG, Hecher K. Doppler sonographic demonstration of arterio-venous anasto-
[8]
[9]
[10]
[11]
[12]
59
mosis in monochorionic twin gestation. Ultrasound Obstet Gynecol 2000;16:214–7. Denbow ML, Cox P, Taylor M, Hammal DM, Fisk NM. Placental angioarchitecture in monochorionic twin pregnancies: relationship to fetal growth, fetofetal transfusion syndrome, and pregnancy outcome. Am J Obstet Gynecol 2000;182:417–26. Machin GA, Feldstein VA, Harrison MR. Higher selective laser occlusion of causative anastomoses in twin to twin transfusion. Twin Res 1999;2:S24. Feldstein VA, Machin GA, Albanese CT, Sandberg P, Farrell JA, Farmer DL. Twin-twin transfusion syndrome: the ‘select’ procedure. Fetal Diagn Ther 2000;15:257–61. Sohn C, Wallwiener D, Kurek R, Hahn U, Schiesser M, Bastert G. Treatment of the twin-twin transfusion syndrome: initial experience using laser-induced interstitial thermotherapy. Fetal Diagn Ther 1996;11:390–7. Denbow ML, Rivens IH, Rowland IJ, Leach MO, Fisk NM, Haar GR. Preclinical development of non-invasive vascular occlusion with focused ultrasonic surgery for fetal therapy. Am J Obstet Gynecol 2000;182:387–92.
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / i j g o
CLINICAL ARTICLE
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy A. Sau a,⁎, M. Weber b , A.H. Shennan c , D. Maxwell d a
Department of Obstetrics and Gynaecology, University Hospital Lewisham, London, UK Paediatric Pathology, Great Ormond Street Hospital for Children, London, UK c King's College London, Guy's Kings and St Thomas' School of Medicine, Maternal and Fetal Research Unit, St Thomas' Hospital, London, UK d Fetal Medicine Unit, St Thomas' Hospital, London, UK b
Received 27 April 2007; received in revised form 15 June 2007; accepted 21 June 2007
KEYWORDS Arteriovenous anastomoses (AVA); Monochorionic twins; Twin-to-twin transfusion syndrome (TTTS); Antenatal detection
Abstract Objectives: To revalidate the detection technique for arteriovenous anastomoses in an unselected group of monochorionic twins, and to make recommendations about its applicability for more widespread use. Methods: Women with monochorionic diamniotic (MCDA) twins were recruited and underwent placental mapping by color Doppler ultrasound. Images of placental maps showing the location and type of anastomoses were saved as digital video clips. After delivery, dye injection study of all the placentas was performed to delineate the site and type of anastomoses. A digital photograph of each injection study was taken and saved. The antenatal ultrasound images and postnatal dye injection studies were compared. Results: 18 sets MCDA twins were evaluated. In 3 cases there was evidence of twin-to-twin transfusion syndrome. Dye injection of 18 placentas revealed 21 arterio-arterial anastomoses (AAA), 21 arteriovenous anastomoses (AVA) and 4 veno-venous anastomoses (VVA). Of these, 10 (48%) AAAs and 5 (24%) AVAs were detected antenatally by color Doppler. In all cases, where an AVA was detected, the placenta was located anteriorly. Conclusion: Antenatal detection of AVA was feasible when the placenta was located anteriorly, but proved difficult in posteriorly situated placentas. © 2007 Published by Elsevier Ireland Ltd. on behalf of International Federation of Gynecology and Obstetrics.
1. Introduction Twin-to-twin transfusion syndrome (TTTS) is the most serious complication of monochorionic twins, affecting about 10%–20% ⁎ Corresponding author. Tel.: +44 02083333000x6214; fax: +44 02086901963. E-mail addresses: [email protected], [email protected] (A. Sau).
of all such twin pregnancies, and with a mortality rate of 80% if untreated [1,2]. Arteriovenous anastomoses (AVA) are a common form of inter-twin vascular connection and are implicated as a causative mechanism in the development of TTTS [3,4] by mediating unbalanced inter-twin transfusion from donor to recipient. Selective laser ablation of AVAs therefore addresses the underlying pathophysiological basis of the disease. Of all the available treatment modalities, it is associated with highest survival rate [5]. However, some
0020-7292/$ - see front matter © 2007 Published by Elsevier Ireland Ltd. on behalf of International Federation of Gynecology and Obstetrics. doi:10.1016/j.ijgo.2007.06.043
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy fetal medicine specialists feel that the initial fetoscopic identification of these anastomoses may prolong the procedure, thereby increasing the risk of spontaneous rupture of membrane. Consequently, antenatal mapping of the vascular equator by color and spectral Doppler might be helpful in reducing the duration of the procedure. Two preliminary reports involving 7 pairs of highly selective monochorionic twins have shown that specific arteriovenous anastomoses can be visualized by using specialized color Doppler ultrasound techniques [6,7]. If this technique could be replicated reliably and then found capable of incorporation into clinical practice, a considerable advance in the management of twin pregnancies would have been achieved. The aims of our study were to revalidate the clinical efficacy of the color Doppler technique, to perform the evaluations in a larger group of unselected monochorionic twin pregnancies, and to make recommendations about its applicability for more widespread twin surveillance.
2. Materials and methods This study was conducted from September 2002 to December 2003. Pregnant women were recruited from the Twin Ultrasound Surveillance Clinic after confirmation of monochorionic placentation. These patients were normally seen in this clinic fortnightly or more often, as clinically indicated. In addition to the standard ultrasound examination routinely performed on these patients, those recruited had undergone color Doppler examination of the fetal surface of the placenta to try to identify anastomosing vessels using high resolution, real time sonographic equipment (5–8 MHz Elegra; Siemens, Stockton, CA, USA). This study was approved by the Guy's and St Thomas' Research Ethics Committee. Placental mapping was performed using the technique described by Machin et al. [7]. The technique involves the standard location of the placental cord insertion sites using greyscale and color Doppler techniques. The placental tissue situated between the two cord insertion sites was then interrogated using color Doppler to identify an unaccompanied unpaired vascular structure on the fetal surface of the placenta. Once identified the cursor gate was placed within this vascular structure to demonstrate arterial flow in one segment and venous flow in the other segment
Figure 1 Dye injection of the placenta showing the site of arteriovenous anastomosis (yellow arrow).
57
of the vessel. The flow direction was similar in both arterial and venous portions. Images of placental maps showing the location and type of anastomoses were saved as digital video clips. All women were scanned by one sonographer (AS). After delivery, all placentas were examined by a perinatal pathologist. Macroscopic identification of anastomoses was recorded in the notes before injection of dye into the placental vessels using the method of Denbow et al. [8]. Digital photographs of each injection study were taken and saved (Fig. 1). Comparison of the antenatal ultrasound images regarding type and location of anastomoses and postnatal dye injection studies were performed. Perinatal outcome of all monochorionic diamniotic (MCDA) twins were recorded.
3. Results During the study period 30 women attended the twin surveillance clinic, of which 20 agreed to participate in the study. In 2 cases, although antenatal placental mapping was performed, postnatal dye injection was not possible because of delay in examining the placenta. Both antenatal and postnatal examinations were completed in 18 cases. In 3 cases there was evidence of twin-to-twin transfusion syndrome (Table 1). Case 4 went into premature labor the day after amnioreduction of 1.5 L; case 6 was delivered by elective cesarean delivery after 3 amnioreductions; and case 9 was delivered without any antenatal intervention. The placental locations were anterior in 10 cases, posterior in 7 cases, and fundal in 1 case. Four women were obese with body mass index (BMI) of N 30. As shown in Table 1 it was possible to detect arteriovenous anastomoses (AVA) on only 5 occasions. In 4 cases it was detected between 20 and 26 weeks of gestation, and in another case it was detected at 28 weeks. Dye injection of 18 placentas revealed 21 arterio-arterial anastomoses (AAA), 21 arteriovenous anastomoses (AVA), and 4 veno-venous anastomoses (VVA). Of these, 48% AAAs and 24% AVAs were detected antenatally by color Doppler. In all cases, where AVA was detected, the placenta was located anteriorly.
4. Discussion Identification of arteriovenous anastomoses by non-invasive Doppler ultrasound technique may prove highly valuable in the obstetric management of MCDA twins. This information has been used in the planning and performance of fetoscopic laser coagulation with successful outcomes [9,10]. Furthermore, Doppler could direct non-invasive treatment such as interstitial laser or focused ultrasound therapy for the occlusion of arteriovenous anastomoses [11,12]. This technique can be seen to have two potential clinical applications: a primary role in identifying pregnancies at risk of TTTS, and a secondary role in facilitating treatment if TTTS develops. Unfortunately, the technique has technical constraints: obese patients, posterior placentas, and earlier gestation when the vessels are still quite small. The present series used the techniques of Machin et al. [9]. It was possible to detect the AVAs on only 24% of occasions despite rigorous scanning attempts. The low detection rate in this series may reflect an unselected population. Posteriorly situated placentas (7 of 18 cases) and maternal obesity (BMIN 30 in 4 cases) was thought to contribute to the failure rate. In majority
58 Table 1
A. Sau et al. Comparison of antenatal detection and postnatal dye injection of anastomotic vessels in MCDA twins
Case
Diagnosis
Placenta location
Gestation at placental mapping (weeks)
Detection of anastomoses by ultrasound
Gestation at delivery (weeks)
Mode of delivery
Birth weight (g)
Detection of anastomoses by dye injection
1
MCDA
Posterior
22
Nil
38
SVD
2760 2540
2
MCDA
Anterior
24
1 AAA 1 AVA
38+ 4
Em LSCS
2390 3240
3
MCDA
Posterior
26
1 AAA
38
4
MCDA TTTS MCDA
Anterior
26
1 AVA
26+ 3
El LSCS SVD
Anterior
28
2 AAA
38
Anterior
28
1 AVA
32
7
MCDA TTTS MCDA
Anterior
24
Nil
38
Em LSCS El LSCS Em LSCS
8
MCDA
Anterior
20
Nil
36
SVD
9
Posterior
22
Nil
29+ 5
10
MCDA TTTS MCDA
Posterior
24
Nil
38
Em LSCS SVD
11
MCDA
Posterior
22
Nil
38
12
MCDA
Anterior
28
1 AAA
38
13
MCDA
Fundal
24
1 AAA
38+ 5
14
MCDA
Anterior
22
1 AAA 1 AVA
38
2640 2370 840 460 2860 2630 1255 1980 3200 2800 2500 1900 1008 1590 2550 2660 2082 2087 2530 2520 2500 1920 1720 1753
1 AAA 1 AVA 1 VVA 2 AVA (T1–T2) 3 AVA (T2–T1) 1 AAA 1 AVA (T1–T2) 1 AVA (T2–T1) 2 AAA 1 AVA 2 AAA 1VVA 1 AVA
15
MCDA
Anterior
20
1 AVA
34
Em LSCS
1540 2360
16
MCDA
Posterior
22
1 AAA
34
17
MCDA
Posterior
24
Nil
36
Em LSCS SVD
18
MCDA
Anterior
20
2 AAA
38
SVD
1940 1639 2200 2100 2350 2670
5 6
El LSCS Em LSCS Em LSCS SVD
1VVA 1 AAA 1 AVA 2 AAA 2 AVA 1 AAA 1 AAA 1 AVA 1 AAA 1 AVA (T1–T2) 2 AVA (T2–T1) 1 AAA 1 VVA 2 AVA (T1–T2) 1 AVA (T2–T1) 1 AAA 2 AAA 2 AAA 1 AVA 3 AAA
Abbreviations: TTTS, twin-to-twin n transfusion syndrome; AAA, arterio-arterial anastomoses; AVA, arteriovenous anastomoses, VVA, venovenous anastomoses; Em, emergency; El, Elective; LSCS, lower segment cesarean delivery; SVD, spontaneous vaginal delivery; T1–T2, twin 1 to twin 2; T2–T1, twin 2 to twin 1; MCDA, monochorionic diamniotic.
of the cases, detection of anastomoses was made at or after 20 weeks, and this may be due to smaller vessel size at earlier gestation. In our opinion, attempts to detect AVA should be made from 18 weeks of gestation. With advances in ultrasound technology, such as the use of high definition ultrasound with 4D technology and dynamic magnetic resonance imaging, the detection rate is likely to improve. From this study it can be concluded that antenatal detection of arteriovenous anastomoses was feasible, and the technique reproducible. However, further work to reduce
or eradicate the technical constraints and reduce the failure rate are necessary before this technique can be recommended for routine clinical application.
References [1] De Lia JE, Kuhlmann RS, Harstad TW, Cruikshank DP. Fetoscopic laser ablation of placental vessels in severe previable twin-twin transfusion. Am J Obstet Gynecol 1995;172:1202–8.
Antenatal detection of arteriovenous anastomoses in monochorionic twin pregnancy [2] Fisk NM, Taylor MJO. The fetus(es) with twin twin transfusion syndrome. In: Harrison M, Evans M, Adzick S, Holzgreve W, editors. The unborn patient: the art and science of fetal therapy. Philadelphia: W.B. Saunders Company; 2000. [3] Machin G, Still K, Lalani T. Correlations of placental vascular anatomy and clinical outcomes in 69 monochorionic twin pregnancies. Am J Med Genet 1996;61:229–36. [4] Bajoria R, Wigglesworth J, Fisk N. Angioarchitecture of monochorionic placentas in relation to the twin-twin transfusion syndrome. Am J Obstet Gynecol 1995;172:856–63. [5] Quintero RA, Morales WJ, Mendoza G, Allen M, Kalter CS, Giannina G, et al. Selective photocoagulation of placental vessels in twin-twin transfusion syndrome: evolution of a surgical technique. Obstet Gynecol Surv 1998;53:S97–S103. [6] Taylor MJ, Farquharson D, Cox PM, Fisk NM. Identification of arterio-venous anastomoses in vivo in monochorionic twin pregnancies: preliminary report. Ultrasound Obstet Gynecol 2000;16:218–22. [7] Machin GA, Feldstein VA, van Gemert MJ, Keith LG, Hecher K. Doppler sonographic demonstration of arterio-venous anasto-
[8]
[9]
[10]
[11]
[12]
59
mosis in monochorionic twin gestation. Ultrasound Obstet Gynecol 2000;16:214–7. Denbow ML, Cox P, Taylor M, Hammal DM, Fisk NM. Placental angioarchitecture in monochorionic twin pregnancies: relationship to fetal growth, fetofetal transfusion syndrome, and pregnancy outcome. Am J Obstet Gynecol 2000;182:417–26. Machin GA, Feldstein VA, Harrison MR. Higher selective laser occlusion of causative anastomoses in twin to twin transfusion. Twin Res 1999;2:S24. Feldstein VA, Machin GA, Albanese CT, Sandberg P, Farrell JA, Farmer DL. Twin-twin transfusion syndrome: the ‘select’ procedure. Fetal Diagn Ther 2000;15:257–61. Sohn C, Wallwiener D, Kurek R, Hahn U, Schiesser M, Bastert G. Treatment of the twin-twin transfusion syndrome: initial experience using laser-induced interstitial thermotherapy. Fetal Diagn Ther 1996;11:390–7. Denbow ML, Rivens IH, Rowland IJ, Leach MO, Fisk NM, Haar GR. Preclinical development of non-invasive vascular occlusion with focused ultrasonic surgery for fetal therapy. Am J Obstet Gynecol 2000;182:387–92.