1 Centre for Surgical Technologies, Faculty of Medicine, Katholieke Universiteit Leuven and the Departments of 2 Obstetrics & Gynaecology and 3 Thoracic Surgery, University Hospitals, Leuven, Belgium
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Abstract |
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Key words: amnion/fetal membranes/fetoscopy/preterm premature rupture of the membranes/rabbit
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Introduction |
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Mid-gestational amniocentesis is associated with a 12% risk of persistent amniotic leak (Tabor et al., 1986; Gold et al., 1989
; Reece, 1997
). Diagnostic fetoscopy, as practised for diagnostic purposes in the 1970s, was associated with a 48% risk for PPROM (Holzgreve, 1988
; Grannum and Copel, 1990
). Fetoscopy is still rarely used in fetal medicine, but currently suggested as an access modality for in-utero diagnosis and surgery in selected conditions. Nd:YAG laser coagulation for fetofetal transfusion syndrome (FFTS) is associated with a PPROM rate of ~10% (Ville et al., 1998
). More complex fetoscopic procedures such as cord ligation are associated with a PPROM rate of >30% (Quintero et al., 1996b
; Deprest et al., 1998b
). Suggested predictive factors for membrane rupture are; experience of the operator, the duration of and extent of manipulation during the procedure, the diameter of the needle used and gestational age (GA) (Deprest et al., 1997
). Wide application of operative fetoscopy will be limited by this relatively high risk for `iatrogenic' PPROM. In analogy to preterm labour following hysterotomy in case of so-called `open' fetal surgery, the former was called the Achilles heel of fetoscopic surgery (Adzick and Harrison, 1994
; Deprest et al., 1996
). Therefore research is needed to document risk factors and ultimately prevent these membrane-related side-effects of mid-trimester fetoscopy. The development of techniques for closing the membrane defect created at the access sites appears to be a logical approach. Different closure techniques are used or have been proposed for fetoscopic procedures (Genz, 1979
; Anger, 1986
; Baumgartem and Moser, 1986
; Quintero et al., 1996a
; Sener et al., 1997
), but to our knowledge few of them have been evaluated in experimental conditions. We developed an experimental model for creation of membrane defects following fetoscopy (Gratacós et al., 1999
). In the present paper, we use this model to study the efficacy of different techniques for closing fetoscopic access sites.
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Materials and methods |
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A liberal midline abdominal incision was made to expose the pregnant uterus. First, gestational sacs were counted and numbered. A maximum of one in three amniotic sacs, with exclusion of the gestational sacs above the cervix, was randomly assigned to five study groups, according to the closure technique to be tested (n = 72). The others served as negative controls (n = 216; Table I).
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At 3031 days GA does and fetuses were euthanized with a T61 injection (Hoechst, Brussels, Belgium), to undergo a second-look laparotomy. A myometrial incision was made on the antimesenterial side, starting over the first cornual sac. The incision was continued over the full length of the horn, both over treated and control sacs. Under microscopic control, the myometrium was gently dissected using microsurgical instruments. Main outcome measurements were integrity of both chorionic and amniotic membranes and presence or absence of amniotic fluid, as observed under the microscope. In case of an intact amniotic membrane, integrity was double checked by an intra-amniotic injection of 510 ml of saline, dyed with methylene blue. The injection was done with a 30 gauge needle through the membrane opposite the former fetoscopic access site. With this injection any possible leak accidentally missed before, would be visualized. The fetus was then delivered and for each fetus it was noted if it was alive or not. They were weighed, and dissected to assess the wet fetal lung weight (FLW) and to calculate the wet fetal lung-to-body-weight ratio (FLBWR). Macerated stillborn fetuses were noted as non-surviving and not further included in statistical processing. Initially, there were two more rabbits included in this study, but one of them aborted and one died. No obvious reason could be found at the time of necropsy. These animals were excluded from the study.
All animals were treated in accordance with the current guidelines on animal welfare and the experiments were approved by the Ethical Committee for Animal Experimentation of the Faculty of Medicine of the Katholieke Universiteit Leuven. Where appropriate, statistics were done with 2 Fisher's exact two-tailed test for nominal variables, and unpaired Student's t-test or analysis of variance (ANOVA) for continuous variables using a SAS software package (SAS Institute Inc., Haasrode, Belgium). Membrane integrity of groups IIV were compared to negative and positive controls and against each other. FLW and FLBWR of intact and open gestational sacs were compared.
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Results |
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FLBWR in sacs with and without membrane integrity were compared (Table III). In gestational sacs with persistent membrane defects at term, FLBWR was significantly lower than in fetuses from treated but intact gestational sacs by the time of the second-look operation [0.0256 (SD 0.005) versus 0.0288 (SD 0.003); P < 0.05]. This remained significant when comparing to negative controls with intact membranes [0.030; (SD 0.017) P < 0.05]. Numbers were too low to allow statistical analysis of pulmonary parameters within individual study groups.
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Discussion |
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A potential way to prevent iatrogenic PPROM might be to close or seal the membrane defect at the time of the intervention. Several techniques are used or have been suggested to close the fetoscopic access site, but their effect on the risk of PPROM is unclear. The uterine access mode may influence the technique used. Only a few fetoscopic procedures are done with partial or complete exposure of the uterine wall through maternal laparotomy. In this case, the uterus may be closed by a purse string, which arrests immediate fluid leak or potential uterine wall haemorrhage (Luks et al., 1997; Deprest et al., 1998b
). However, most fetoscopies today are done with a percutaneous approach. After withdrawal of the endoscope, the entry site is left unclosed and the myometrial defect probably closes by uterine contraction. When considering sealing the entry site percutaneously, the use of liquid agents or plugs is intuitively the most feasible approach.
The concept of sealing the site of disruption with fibrin glue had already been suggested for spontaneous PPROM (Genz, 1986), but this technique was never widely implemented because of lack of efficacy (Anger, 1986
; Baumgartem and Moser, 1986
; De Lia et al., 1990
). In our early clinical experience, we used this glue to seal the trocar site following a fetoscopic cord ligation, but an amniotic band syndrome occurred in that patient (Deprest et al., 1996
). Fear of a potential causal relationship and the lack of experimental evidence precluded further implementation of this technique. Successful treatment of PPROM following fetoscopic cord ligation has been reported using an intra-amniotic platelet-cryoprecipitate plug (Quintero et al., 1996a
). Following the same line, full maternal blood has been used successfully to patch the entry site in a case of persistent amniotic fluid leak after amniocentesis at 16 weeks (Sener et al., 1997
). However, additional clinical experience confirming the successful outcome described in these case reports continues to be lacking.
Anecdotal experience is clearly not enough to support wide implementation of sealing techniques and therefore experimental work to estimate the real efficacy and potential complications of any proposed technique seems justified. We have previously described the mid-gestational rabbit model to test out closure techniques of hystero-amniotomy sites as performed in open fetal surgery (Papadopulos et al., 1998). In that study, a 1 cm hystero-amniotomy resulted in a permanent large membrane defect with anhydramnios in 100% of cases. Among the various techniques evaluated, closure of the myometrium was associated with the highest rate of postoperative amniotic integrity. We have later used a comparable protocol in the same animal model to produce fetoscopy-induced membrane defects (Gratacós et al., 1999
). In that study, we demonstrated that fetoscopy induced a persistent membrane rupture rate of ~40% which was accompanied by pulmonary hypoplasia. Thus the model resembled the complications of oligohydramnios in humans and was suitable for studies aiming to modify the rate of membrane defects following fetoscopy.
In the present study, we have used the rabbit model to assess the efficacy of some techniques that may be considered for closing the access site following fetoscopy. Most of these techniques are applicable by a percutaneous approach (groups IIIV). Myometrial closure (group I) was also tested, since it yielded the best results in our previous study on hystero-amniotomy incisions (Papadopulos et al., 1998). However, none of the tested techniques improved the spontaneous rate of restored membrane integrity. The fetal pulmonary complications of oligohydramnios were also present in fetuses from treated sacs but with persistent membrane defects. There may be different reasons for this relatively poor performance. It is possible that plugs became dislodged in the postoperative course (groups IIIV). The lack of improvement associated to the use of myometrial suture could reflect that this approach does not address the membrane defect adequately.
Finally, as with any animal experiment, there are limitations for extrapolating results to human pregnancy. In any case, these discouraging results illustrate the need for experimental work testing any proposed technique prior to its clinical application. Combinations of techniques, more appropriate platelet preparations or more species-specific fibrin sealant or collagen plugs could be also tested.
In conclusion, clinical experience with operative fetoscopy stresses the need for techniques to prevent or treat membrane defects. None of the surgical techniques evaluated in a pregnant rabbit model could improve spontaneous resealing rates of fetal membranes following an invasive procedure such as fetoscopy. Among the possible directions for future research, a combination of different techniques may be considered, but additional research should go deeper into the mechanism of spontaneous membrane remodelling following iatrogenic trauma, both at the morphological and the molecular level.
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Acknowledgments |
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This study was supported by the Biomed 2 Programme of the European Community (`Eurofoetus`, grant N° PL 962383). E.G. is the recipient of a research fellowship from the European Commission.
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Notes |
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References |
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Submitted on December 29, 1998; accepted on April 1, 1999.