Dr Roopa R Shinde Specialist, Fetal medicine, Institute – Medcare Women and Children, Dubai Email: [email protected] medcarehospital.com
Key words Monochorionic twin, twin to twin transfusion syndrome, selective intra uterine restriction.
Conflict of interest There are no conflicts of interest to report and no external funding sources.
Monochorionic twin pregnancies, by virtue of vascular anastomoses, are at risk of unique compli- cations. These include Twin-To-Twin Transfusion Syndrome (TTTS), Selective Intrauterine Growth Restriction (sIUGR), and Twin Reverse Arterial Perfusion (TRAP) sequence. Vascular anastomoses are present in every monochorionic placenta; these represent a state of imbalance in the shunting of blood, or an abnormality in the nature of anatomis- ing vessels, which forms the basis for these unique clinical entities. The extreme circumstances of these complications eventually lead to single foetal demise in such twins. The intra-uterine demise of one fetus results in the acute transfer of intravascular volume from the co-twin to the dying twin (rescue transfu- sion), resulting in exsanguination with accompanying hypotension, anaemia, death and ischaemic cerebrovascular insults to the co-twin. The demise of one foetus in a monochorionic gestation is as- sociated with co-foetal demise in 12–25% of cases, and a risk of neurological abnormalities in 18–25% of surviving infants.1
Umbilical artery Doppler flow is the parameter whichbestreflectsthe difference ingrowthrestric- tionbetween monochorionic and dichorionic twins; Changes in flow within the umbilical artery are closely related to clinical changes and outcomes. Foetuses with positive diastolic flow have a benign prognosis, whilst foetuses with intermittent absent or reversed diastolic flow have a high risk of intra-uterine foetal demise, and consequently ischaemic damage, especially parenchymal brain damage, to the normally growing twin. Under such circumstances, selective termination of one foetus optimizes the chances of survival of the co-twin. Selective foetal reduction is known to improve the perinatal outcome in the extreme situations caused by this complication of monochorionicity. 2,3 Inter- ventional procedures such as intra-cardiac injection of cardio toxic agents like potassium chloride cannot be carried out in monochorionic pregnancies, because of the risk of a drug being transferred to the co-twin via the anastomosing vessels. Selective terminationinmonochorionic pregnanciesinstead requires ablation of the blood flow in the umbilical cord, to prevent acute intra-foetal transfusion.
We present here a case of TTTS with sIUGR, for which growth restriction typing was completed according to the classification criteria proposed by Gratacos et al.4 TTTS was classified based on the Quintero system.5
A 39-year-old gravida 2, para 1, living 1 (previous LSCS) patient was referred to the foetal medicine unit of MWCH, for a second opinion on a monochorionic diamniotic twin pregnancy with TTTS at 20 weeks of gestation. Her blood group was rhesus A positive. All recent menstrual cycles were regular and there was no significant medical, surgical and family history. The patient had conceived naturally. At a scan at 12 weeks of gestation, a diagnosis of monochorionic diamniotic twin pregnancy was made. The foetuses were concordant for liquor growth and aneuploidy markers. The first trimester screen was negative for aneuploidies, with all biochemical parameters within the normal limits.
On referral, Monochorionicity was confirmed through the ultrasound findings of a single placenta, a thin intervening membrane and lack of a lambda sign. A detail target scan with Doppler study and foetal echo was carried out. Our findings were a monochorionic twin pregnancy atagestational age of 20 weeks and 3 days, with an anterior common placenta (gestational age was assigned as per the last menstrual period). The twins were discordant for liquor, bladder, growth and Doppler flow. Twin A had no measurable liquor pocket, suggestive of anhydramnios, and the single deepest pocket of liquor for twin B was 8.7cm.The bladder was absent for twin A and distended for twin B. Estimated foetal weights were 225 g and 356 g for twin A and B respectively. The weight discordancy between the foetuses was 37%.
Twin B was structurally normal for the period of gestation. The anatomical survey was limited for twin A due to anhydramnios. The Doppler study of twin A showed an intermittent absent dia- stolic flow pattern in the umbilical artery (type 3 Gratacos), with normal flow in the Ductus venosus and middle cerebral artery. Twin B gave normal Doppler results, and was haemodynamically stable. The CHOP (Children’s Hospital of Philadelphia cardiovas- cular score in twin to twin transfusion syndrome) score was 0. A final diagnosis was made, of a monochorionic twin preg- nancy, discordant for bladder, liquor, growth and Doppler, with features suggestive of twin to twin transfusion syndrome stage 2 with selective intra uterine growth restriction of twin A type 3. The couple was counseled accordingly. All abnormal findings were confirmed with repeated sittings and multiple measure- ments (especially the absence of a bladder and the Doppler findings for twin A). The Doppler study was performed following the guidelines (ISUOG practise guidelines 2013).
The family was briefed on the findings, their implications and the consequences in the setting of monochorionicity. The benefits and risks of conservative management versus intervention, and in particular in intervention the option of laser ablation of placental vessels versus selective foetal reduction, were all dis- cussed in length. The family opted for selective foetal reduction. A selective foetal reduction was conducted, via radiofrequency ablation. After in-house monitoring for 48 hours post-procedure, the pregnancy was followed up with Doppler and growth study fortnightly for two months . Twin B was haemodyamically stable throughout, and maintained an estimated foetal weight of between 30 – 33 % until 30 weeks. At 33 weeks, we observed a slight drop in the biometry parameters (estimated foetal weight 22%) and the liquor volume. Steroids were administered to prompt lung maturity. At 34.3 weeks the liquor further reduced (AFI < 5 cm), andasuboptimal CTG reading wasrecorded, follow- ing which the patient was posted for an elective LSCS. A female baby weighing 2.120 kg was delivered with a good APGAR score.
The baby was observed in the NICU and was started on feeds the second day. A brain USG was normal and all screenings tests (new-born metabolic and hearing screen tests) were also normal.
The management of growth restriction in monochorionic twin pregnancies represents a challenge, and even moreso when it is co-existent with TTTS. Classification of sIUGR into types, based on the characteristics of umbilical artery diastolic flow in the IUGR twin, permits differentiation clinically, and is helpful in prognosticating, counselling and clinical decision-making.4 sIUGR type 1 has normal diastolic flow, and relatively good outcomes. Type 2 is defined by persistently absent/reverse end- diastolic flow and is associated with a high risk of intrauterine demise of the IUGR twin, and/or very preterm delivery. Type 3 is defined by the presence of intermittent absent/reverse end- diastolic flow (iAREDF), and is associated with a 10-20% risk of unexpected foetal demise of the smaller twin and a 10-20% risk of neurological injury in the larger twin.3
This case had type 3 sIUGR with TTTS stage 2. The deter- minants of grading the severity of sIUGR (GA <22 weeks or discordancy > 35% or AREDF or DV PI >p95) were all hostile to expectant management. Left to its natural evolution, with these findings at as early as 20 weeks, the outcomes would certainly have been adverse. Delivery would have been indicated if the gestation was greater than 26 weeks.6 Expectant management may be associated with the very preterm birth of both twins, and the inherent morbidity associated with prematurity.7
In monochorionic pregnancies, selective foetal termination can be considered in an attempt to salvage at least one foetus, especially when the entire pregnancy is at threat. However, the final decision among therapy options will be influenced by the severity of growth restriction, the preferences of parents, and technical issues.
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