Conjoined Twins

Conjoined twins are monozygotic twins whose bodies are united, resulting from incomplete splitting of the embryo after day 13 after fertilisation. They are rare and are more often female. Types are named by the site of union: thoracopagus (chest), omphalopagus (abdomen), pygopagus (buttocks), ischiopagus (pelvis), craniopagus (head), parapagus (side) and cephalopagus (face and chest). It matters because survival depends on shared organs (especially the heart), and counselling, place of birth and surgical planning need early detail.

• Risk factors: none known; not inherited.
• Always monochorionic monoamniotic.
• Many are stillborn or die soon after birth.

Women are usually well, with a uterus larger than dates, polyhydramnios in many and fetal parts that appear fixed together. In late pregnancy the twins cannot change relative position.

• Fixed relative position of the two fetuses.
• Polyhydramnios.
• Differential diagnosis: monochorionic monoamniotic twins with entanglement, twin to twin transfusion syndrome, fetus in fetu, teratoma, single fetus with duplicated structures.
• Complications: heart failure, stillbirth, obstructed labour, uterine rupture, preterm labour, neonatal death, difficult birth, postpartum haemorrhage, psychological harm to the parents.

The approach is detailed ultrasound at 11 to 14 weeks, with MRI and echocardiography.

• Ultrasound at 11 to 14 weeks: twins that do not move apart, bodies in constant contact at one level, heads in a fixed position, a single shared yolk sac or sac; transvaginal and three dimensional scans.
• Detailed anomaly scan to define the union and shared organs; fetal echocardiography to define the heart, which decides survival; fetal MRI for shared brain, liver, bowel and kidneys.
• Karyotype if amniocentesis is accepted.
• Where ultrasound is unavailable, suspect the diagnosis in an obstructed labour or in a twin pregnancy with unusual fetal positions, and refer for caesarean section.

The principle is early diagnosis, counselling on options and outlook, delivery by caesarean section in a tertiary centre and neonatal surgical planning.

• Supportive: refer at once to a fetal medicine unit with paediatric surgery; multidisciplinary counselling with the parents on prognosis, the option of termination within the law (offered when the heart is shared or the anomalies are not compatible with life), comfort care and the option of continuing the pregnancy; psychological and social support; birth in a unit with neonatal intensive care and paediatric surgery.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if preterm delivery is planned; cefazolin 2 g IV before caesarean section; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks if delivered before 32 weeks; oxytocin 10 IU IM at birth then infusion of 20 IU in 1 litre sodium chloride 0.9 percent at 125 mL per hour for 4 hours; carboprost 250 micrograms IM every 15 minutes (maximum 8 doses) for atony, avoided in asthma; tranexamic acid 1 g IV over 10 minutes for bleeding above 500 mL.
• Procedures: termination of pregnancy where requested before viability and allowed by law, using mifepristone 200 mg oral then misoprostol 400 micrograms vaginal or sublingual 3-hourly (maximum 5 doses) 24 to 48 hours later; planned classical caesarean section at 34 to 36 weeks, or earlier for contractions, rupture of membranes or fetal compromise; vaginal birth is not safe except for very early stillbirth or severe pre-viable anomalies; newborn resuscitation and staged or emergency separation by paediatric surgeons at 2 to 6 months or earlier for emergency.
• Special groups: twins with a shared heart or severe untreatable anomalies carry a very poor outlook, and the family is offered counselling about comfort care and about timing of delivery; twins with separate hearts and shared lower body structures have a good outlook after staged separation.
• Red flags: contractions, polyhydramnios, hydrops, reduced fetal movements, bleeding, obstructed labour.
• Follow-up: scans every 2 weeks; neonatal intensive care and surgical planning after birth; psychological support for the family; genetic counselling for the next pregnancy.