Congenital MalformationsThe incidence of congenital malformations is appreciably increased in twin and higher-order multiple gestation compared with singletons. Major malformations develop in 2% and minor malformations in 4% of twins.
Anomalies in monozygotic twins generally fall into one of three categories.
- Defects resulting from twinning itself: This category includes conjoined twinning, acardiac anomaly, sirenomelia, neural tube defects, and holoprosencephaly
- Defects resulting from vascular interchange between monochorionic twins: Vascular anastomoses can give rise to reverse flow with acardia in one twin. Alternatively, if one twin dies and intravascular coagulation develops, these connections can allow emboli to reach the living twins. Vascular connections may also conduct dramatic blood pressure fluctuations, causing defects such as microcephaly, intestinal atresia, aplasia cutis, or limb amputation.
- Defects that occur as a result of crowding: Examples include talipes equinovarus (clubfoot) or congenital hip dislocation. Dizygotic twins are 'also subject to this.
Approximately 1% of monozygotic twins are monoamnionic.
A high fetal death rate is associated with this rare variety of monozygotic twinning. Intertwining of their umbilical cords, a common cause of death, is estimated to complicate at least half of cases.
Conjoined twins (TOPIC) (in descending order of frequency):
- Thoracopagus (joined at thorax), MC variety
- Omphalopagus (abdomen)
- Pygopagus (buttocks)
- Ischiopagus (ischium)
- Craniopagus (head), least common variety
- Twin-to-twin transfusion syndrome (occurs in monochorionic twins only):
- In this syndrome, blood is transfused from a donor twin to its recipient sibling such that the donor becomes anemic and oligohydramnios, and its growth may be restricted, whereas the recipient has polyhydramnios and becomes polycythemic and may develop circulatory overload manifest as hydrops. Similarly, one portion of the placenta often appears pale compared with the rest of the placenta.
- This is due to deep arteriovenous anastomosis.
- Antenatal criteria recommended for defining the twin-to-twin transfusion syndrome include the following: same sex fetuses, monochorionicity with placental vascular anastomoses, weight difference between twins greater than 20%, polyhydramnios the larger twin, oligohydramnios in donor twin, and hemoglobin difference greater than 5 g/ dL.
- The donor twin has better prognosis.
- Acardiac twin: Twin reversed arterial perfusion (TRAP) sequence is a rare (1 in 35,000 births) but serious complication of monochorionic, monozygotic multiple gestation. In the TRAP sequence, there is usually a normally formed donor twin that has features of heart failure as well as a recipient twin that lacks a heart (acardius) and various other structures.
- Discordant growth (can occur in DZ and MZ twins): There is difference in weights of twins and is expressed as % of larger twin's weight:
- Route of delivery is decided by the position of first baby.
- Only if the first fetus is in vertex position, then normal vaginal delivery is possible.
- Twins with first fetus in nonvertex position (breech, transverse, oblique, ...) are to be delivered by LSCS.
- MC, MA twins are always to be delivered by LSCS (even if the first fetus is in vertex position) because of very high risk of cord prolapse and cord entanglement.