Managing risk—to mother and fetuses—in a twin gestation
Begin by determining chorionicity. Discuss the risks of a multiple gestation, prepare parents for premature delivery, and monitor fetal growth as indicated.
IN THIS ARTICLE
The diagnosis of twin-to-twin transfusion syndrome (TTTS) depends on the presence of a single monochorionic placenta and abnormalities in the volume of amniotic fluid (the polyhydramnios–oligohydramnios sequence). The syndrome may have an abrupt or gradual onset, heralded by discordancy and restriction in the growth of the 2 fetuses.
The natural history of the syndrome and treatment outcome are based on a staging system described by Quintero and colleagues1:
Stage I is characterized by polyhydramnios–oligohydramnios with the bladder still visible in the donor twin
Stage II The donor bladder is no longer visible
Stage III is defined by abnormal Doppler studies showing absent or reversed flow in the umbilical artery, reversed flow in the ductus venosus, or pulsatile umbilical venous flow
Stage IV is indicated by hydrops in either twin
Stage V One or both twins die.
The prognosis for TTTS grows poorer with increasing stage and is poor if the condition goes untreated, with a reported survival rate of only 25% to 50% for 1 twin when the diagnosis is made in the second trimester.2,3 Treatment options include removal of excess amniotic fluid through serial amniocenteses (amnioreduction), fetoscopic laser coagulation of communicating vessels, selective fetocide, and perforation of the membrane that separates the twins (septostomy).
Serial amnioreduction is the most common procedure for treating TTTS. When Senat and colleagues compared the efficacy of serial amnioreduction with fetoscopic laser occlusion in a randomized control trial, however, they found that the laser group had a significantly higher likelihood of survival of at least 1 twin (76%) than the amnioreduction group (56%).4
Septostomy. A recently published randomized trial in which amnioreduction was compared with septostomy found no difference in survival between the 2 treatments.5 Septostomy often has the advantage of requiring only 1 procedure to be successful, whereas repeated amniocenteses are necessary in serial amnioreduction. Septostomy does carry the risk of creating a single amnion, as the size of the membranous defect created by the perforation is difficult to control.
Selective fetocide using US-guided cord occlusion or radiofrequency ablation has been described when there is a coexisting fetal anomaly, growth restriction, or a chromosomal abnormality in 1 twin (heterokaryotypia).6,7 Use of bipolar coagulation in this setting has been associated with a liveborn in 83% of cases and intact neurologic survival in 70%.7 Radiofrequency ablation has also been described for selective fetal termination in monochorionic placentation with an abnormality in 1 twin.6 Data presented at the 2006 annual meeting for the Society for Maternal–Fetal Medicine showed no difference in the overall complication rate between these 2 techniques of selective fetocide.8
References
1. Quintero RA, Morales WJ, Allen MH, Bornick PW, Johnson PK, Kruger M. Staging of twin–twin transfusion syndrome. J Perinatol. 1999;19:550-555.
2. Berghella V, Kaufman M. Natural history of twin–twin transfusion syndrome. J Reprod Med. 2001;46:480-484.
3. Bromley B, Frigoletto FD, Setroff JA, Benacerraf BR. The natural history of oligohydramnios/polyhydramnios sequence in monochorionic diamniotic twins. Ultrasound Obstet Gynecol. 1992;2:317-320.
4. Senat MV, Deprest J, Boulvain M, Paupe A, Winer N, Ville Y. Endoscopic laser surgery versus serial amnioreduction for severe twin to twin transfusion syndrome. N Engl J Med. 2004;351:136-144.
5. Moise KJ, Dorman K, Lamvu G, et al. A randomized trial of amnioreduction versus septostomy in the treatment of twin–twin transfusion syndrome. Am J Obstet Gynecol. 2005;193:701-707.
6. Robyr R, Yamamoto M, Ville Y. Selective feticide in complicated monochorionic twin pregnancies using ultrasound-guided bipolar cord coagulation. BJOG. 2005;112:1344-1348.
7. Shevell T, Malone FD, Weintraub J, Harshwardhan MT, D’Alton ME. Radiofrequency ablation in a monochorionic twin discordant for fetal anomalies. Am J Obstet Gynecol. 2004;190:575-576.
8. Bebbington M, Danzer E, Johnson M, Wilson RD. RFA vs cord coagulation in complex monochorionic pregnancies. Am J Obstet Gynecol. 2006;195:S192.-
Prenatal diagnosis
Given the lower detection rate of aneuploidy in twin gestations and the associated increase in aneuploidy with advancing maternal age, many patients choose to undergo prenatal diagnosis rather than relying on screening. On the basis of maternal age alone, invasive prenatal diagnosis can be offered to women who will be 31 years or older at their estimated due date.
Available diagnostic options include chorionic villus sampling (CVS) or amniocentesis. CVS is performed at an earlier gestational age (10 to 13 weeks) than amniocentesis (15 to 20 weeks). Multiples pose specific technical considerations for either procedure, and accurate fetal mapping is essential. Successful sampling with CVS can be performed in more than 99% of cases; the rate of cross-contamination is less than 1%.
Is there a risk of miscarriage?
In counseling patients about the risk of fetal death that CVS or amniocentesis may entail, the place to begin is the background loss rate, which is greater in twin than in single gestations. The reported background loss rate of twins at 24 weeks’ gestation or less ranges from 5.8% to 7.2%.20,21 In women of advanced maternal age (35 years and older), a background rate as high as 17.6% has been described.21 Once parents are aware of this, they have a context for weighing the risk of miscarriage that prenatal testing may hold.
