Severe cases of monochorionic twins with SIUGR show ultrasound evidence of abnormal blood flow through the umbilical artery of the poorly grown twin. In this circumstance, spontaneous death of this baby within the womb may occur in up to 40% of cases. Because of the blood vessels that link the twin’s circulatory system together, death of one twin may result in severe drop in blood pressure of the other twin and subsequent brain damage (up to 30%) or death (up to 40%). This complication results from the hemorrhage of blood from the appropriately grown twin into the demised SIUGR twin.Because the adverse effects to the appropriately grown twin is mediated through the blood vessels that link the circulations of the twins, it has been suggested that obliteration of these vascular communications may result in improved outcomes for the normally grown twin. Separation of the circulations may be done using the surgical techniques which were originally developed for the treatment of twin-twin transfusion syndrome.
Diagnosis
The in utero diagnosis of SIUGR is established by ultrasound. First, the presence of a shared placenta (monochorionic) should be confirmed. Usually ultrasounds performed earlier in the pregnancy may be useful in establishing the chorionicity (number of placentas). Ultrasound findings such as a single placenta, same fetal sex, and a “T-sign” in which the dividing membrane inserts perpendicular to the placenta are helpful in diagnosing a monochorionic twin gestation.
Once a monochorionic placentation has been established, the diagnosis of SIUGR requires the presence of three important ultrasound findings:
- The estimated fetal weight (EFW) of one twin measures less than the 10th percentile for the assigned gestational age. The EFW is calculated by measuring standard fetal biometric components via ultrasound. Because prior studies have shown negligible difference between growth curves for singleton and twin gestations in the second trimester, standards as established by Hadlock (1991) for singletons are used to assign the growth percentile.
- Persistent absent or reversed flow in the umbilical artery of the growth-restricted twin.
- Finally, the diagnosis of twin-twin transfusion syndrome (TTTS) must be excluded. TTTS is diagnosed by assessing the discordance of amniotic fluid volume on either side of the dividing fetal membranes; the maximum vertical pocket (MVP) of amniotic fluid volume must be greater than or equal to 8.0 centimeters in the recipient’s sac, and less than or equal to 2.0 centimeters in the donor’s sac to secure the diagnosis of TTTS.
Management Options and Outcomes
The treatment options along with expected pregnancy outcomes are listed below:
- Expectant Management: Prior to the development of the laser therapy outlined below, the treatment of this condition has been traditionally one of expectant management. This entails at least weekly ultrasound assessments of fetal wellbeing, amniotic fluid volume assessment, and Doppler studies of the umbilical artery, as well as sonograms to assess fetal growth about every three weeks. After 24 weeks’ gestation, parents traditionally discuss with their physicians whether there is a need for increased fetal surveillance, such as fetal heart rate monitoring, and if a course of steroids is required for fetal maturation therapy. Early delivery may be decided if fetal status is deemed nonreassuring based on fetal heart rate monitoring or ultrasound parameters. The challenge that this condition presents to parents and physicians alike is in regards to the timing of delivery. On the one hand, delay of delivery will reduce the complications associated with premature birth. On the other hand, prolongation of the pregnancy in this setting, particularly if findings suggestive of a nonreassuring fetal status are present, may result in the demise of one twin in the womb. This may occur in up to 40% of monochorionic twins with SIUGR. As described above, the death of one twin while in the womb may result in the concomitant demise of the other twin in as high as 40% of cases. If the other twin does survive, there is up to a 30% risk of subsequent neurologic handicap. The demise of a twin results in these adverse effects on the other twin because of the blood vessels on the surface of the placenta that connect the circulatory systems of the babies – essentially linking the livelihoods of each baby to one another.
- Laser Therapy: This surgical approach utilizes an operative fetoscope to deliver laser energy that then seals off the offending blood vessels on the surface of the common placenta. Because the vascular connections between the two fetuses are sealed, no further blood exchange between the fetuses takes place. It has been theorized that elimination of the vascular communications may decrease or prevent harm to the surviving twin in the case of the demise of one twin. The magnitude of this potential benefit is unknown.
Candidacy for Treatment
To qualify for treatment, generally the following conditions must be met.
Inclusion Criteria
- Gestational age 16-26 weeks.
- Sonographic evidence of monochorionicity (shared placenta).
- Diagnosis of IUGR present in one twin (fetal weight at or below the 10th percentile for gestational age -Hadlock et al 1991).
- Absent or reverse-end diastolic flow in the umbilical artery in the SIUGR twin.
General Exclusion Criteria
- Presence of twin-twin transfusion syndrome defined as a maximum vertical pocket (MVP) of ≤2 cm in one sac and MVP of ≥8 cm in the other sac.
- Presence of major congenital anomalies (anencephaly, acardia, spina bifida) or intracranial findings in either twin: IVH, porencephalic cysts, ventriculomegaly or other findings suggestive of brain damage.
- Unbalanced chromosomal complement.
- Ruptured or detached membranes.
- Placental Abruption.
- Chorioamnionitis (infection in the uterus).
- Triplets
Details of Surgical Procedure
Most surgeries are performed under local anesthesia with some intravenous sedation. A small incision (3 millimeters or about 1/10th of an inch) will be made and a trocar (small metal tube) will be inserted into the amniotic sac of the normally grown twin. Amniotic fluid may be sent for genetic and microbiology studies. An endoscope (medical telescope) will be passed into the uterus. The blood vessels, which are visible on the surface of the placenta, will be analyzed, and all communicating vessels will be sealed off with laser energy. A second trocar may have to be inserted to complete the surgery, particularly if the placenta is anterior. You will be given antibiotics before and after surgery.
Postoperative Care
Typically, you will remain in the hospital for 1 to 2 days after surgery. You will then be sent home to the care of your primary obstetrician and perinatologist. Follow-up ultrasounds will be scheduled every week for the first month to detect possible intrauterine fetal demise, and monthly thereafter. Delivery will be decided based on obstetrical indications (however it is the recommendation of Fetal Health to have weekly monitoring via ultrasound, NST’s, or other appropriate means.).
Selective Intrauterine Growth Restriction (SIUGR): Intrauterine growth retardation (IUGR) occurs in approximately 10% of monochorionic twins. IUGR in monochorionic twins typically affects only one of the fetuses (selective IUGR, SIUGR). The definition of SIUGR, as it pertains to this discussion, is as follows: (1) one twin measures less than the 10th percentile for the given gestational age, (2) the SIUGR twin has persistent absent or reversed flow in the umbilical artery. Note that amniotic fluid discordance plays no role in the diagnosis of this condition. SIUGR appears to be a distinct condition from TTTS, albeit there may be significant overlap. It is believed that SIUGR develops because of unequal placental share, with SIUGR fetus utilizing a minority portion of the common placenta.
Although the vascular communications of the monochorionic placenta are not involved in the etiology of SIUGR, they still play an important role in regards to perinatal outcome. There is a relatively high likelihood of spontaneous demise of the SIUGR twin, which may result in concomitant demise or severe neurological handicap of the other twin. These complications occur from exanguination of the appropriately grown (AGA) twin into the demised SIUGR twin through placental vascular communications. A recently published observational study monitored 84 consecutive monochorionic twins with discordant amniotic fluid that did not meet criteria for twin-twin transfusion syndrome.1** A subgroup of 19 did meet criteria for SIUGR. The overall survival rate in this subgroup was 60% (23/38 fetuses). The neurological injury rate was not described. In another study, 17 patients with SIUGR were managed expectantly.2 The survival rate of the SIUGR twin was 59%. The rate of short-term neurological complications (includes periventricular leukomalacia, intraventricular hemorrhage, and ventriculomegaly) was 14%.
At this time, the standard of care in treating monochorionic pregnancies complicated by SIUGR is to monitor the pregnancy with ultrasound and/or fetal heart rate monitoring, often in the hospital from 24 weeks gestation until delivery, with the plan to attempt to deliver the twins prior to the demise of the growth restricted fetus. This leads to a virtually 100% prematurity rate, with the ever-present risk of neurological injury to the AGA twin. Are there any other management options for the treatment of this condition aside from selective feticide or pregnancy termination? One possible therapeutic modality is to perform operative fetoscopic ablation of the vascular communications to “unlink” the fates of the twins. In other words, should the growth restricted fetus die, the appropriately grown fetus would not be directly affected. These pregnancies may be managed as an outpatient similar to dichorionic twins complicated by intrauterine growth restriction of one fetus. Quintero et al performed a feasibility study that showed a trend towards decreased rate of neurological deficits in the AGA twin, with 14% rate of neurological injury in the expectantly managed group versus 0% in the laser group.2 A randomized study to compare laser surgery versus standard treatment is currently being conducted in the United States by the USFetus Consortium.
References
1. 44Huber A, Diehl W, Zikulnig L, Bregenzer T, Hackeloer BJ, Hecher K. Perinatal outcome in monochorionic twin pregnancies complicated by amniotic fluid discordance without severe twin-twin transfusion syndrome. Ultrasound Obstet Gynecol 2006;27(1):48-52.
** This is an important paper that describes the natural history of monochorionic twins with amniotic fluid discordance that does not meet criteria for TTTS. A subgroup of patients in this study met criteria for SIUGR, and the perinatal outcomes are reviewed.
2. 45Quintero RA, Bornick PW, Morales WJ, Allen MH. Selective photocoagulation of communicating vessels in the treatment of monochorionic twins with selective growth retardation. Am J Obstet Gynecol 2001;185(3):689-696.
