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.
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.