Incidence of twins, triplets or multiple gestations has increased in present times due to the increased use of assisted reproductive technologies. However, the incidence of uniovular twining has remained unchanged. Plural pregnancies are high risk as the mother is at an increased risk of obstetric hemorrhages, preterm premature rupture of membranes, anemia, preeclampsia and operative interventions. Maternal factors increase the risk to the growth restricted and premature fetuses. Permutation and combinations of abnormal presentations increases the chances of cesarean sections or intrauterine manipulations for the last fetus. Besides these common problems uniovular twins, either monochorionic diamniotic or monochorionic monoamniotic, face unique peril. In monoamniotic twins almost 70% twins will have chronic cord entanglement. Twin to twin transfusion (TTTS) and the other rare (incidence of about 1 in 100,000) but dramatic jeopardy is the conjoined twin.
Twin to twin transfusion syndrome occurs in about 15% of all monochorionic twins wherein the shared placenta has usually an arterial to venous communication. This is usually unidirectional. Rarely bidirectional arterial to arterial anastomoses may be present. The artery to vein anastomosis results in discordant growth as the donor becomes anaemic, oliguric, growth retarded and may die in utero due to exsanguination and the recipient becomes macrososmic, polycythemic, polyuric leading to polyhydramnios, and may die due to circulatory overload. Death of one twin usually results in a better outcome for the survivor. Chorionicity and TTTS are best diagnosed by ultrasonography (USG) before 14 weeks of gestation. The presence of the Lambda sign or the “T” image at the interface between the amniotic membrane and the placenta differentiates the dichorionic placenta from the monochorionic placenta respectively. TTTS can be diagnosed by the presence of growth discordance, same gender of the fetuses and presence of oligohydramnios (< 2 cm maximum vertical liquor pocket) in one amniotic sac and polyhydramnios (> 8 cm maximum vertical liquor pocket) in the other sac. Circulatory overload features may also be seen in severe cases of TTTS. The management of TTTS can be expectant or interceptive. Expectant management includes fortnightly serial USG for discordance in abdominal and head circumferences and amniotic fluid depth in each sac. Severity of the TTTS is assessed by Quintero’s criteria and fetal 2D echo. Severe TTTS requires either fetoscopic guided laser ablation of vascular anastomoses, septostomy and amnioreduction or umbilical cord clamping. Umbilical cord clamping of one twin is done to deliberately save one of the twins when the survival chances for both twins are dismal. Laser ablation of the anastomosis is the best treatment option for severe TTTS.
Conjoined twins are extremely rare. They should be prenatally diagnosed by the sonologist when a monochorionic, monoamniotic placenta is detected. Once diagnosed pregnancy may be terminated, or delivery should be planned by cesarean section to prevent dystocia, obstructed labor and catastrophic uterine rupture. Vaginal birth of undiagnosed conjoined twins has been reported not only in the past but also recently.
We bring one such case of conjoined twins in this issue and one case of TTTS. We hope our readers would gain experience from the cases presented in this November issue of our journal.