Monozygotic twins increase in (compared to IVF), Blastocyst transfer(compared to D2/3 transfer)

 Courtesy : Sarabjeet Singh

….Does Monozygotic twins increase in (compared to IVF), Blastocyst transfer(compared to D2/3 transfer)

Incidence otherwise:

DZ: 70%
MZ: 30%- Split @ < 3 Days: DCDA: 09 %
Split @ 4-7 Days: MCDA: 20%
Split @ 8 Days: MCMA: 01%
Split @ > 12 Days: CONJOINT: 0.3%

Factors associated with MZ twinning:

1. Artificial breach of zona pellucida
† ICSI
† Hatching
† Embryo biopsy

There is a belief (at least theoretically) that an inner mass when forms could potentially herniate through the defect created by ICSI/HATCHING/BIOPSY/PGD needle puncture…so that hour glass (figure of eight) created could split to form monozygotic twins. So in that case chances of MZ twins should be more in assisted hatching compared to ICSI as Zona opening formed by assisted hatching is _25–30 um in diameter, while the puncture site following ICSI is much smaller (7–8 um in diameter).paradoxically meta-analysis found a higher incidence of monozygotic twinning after ICSI than after assisted hatching.

2. Transfer of Day 5 blastocyst stage embryos compared with transfer of Day 3 cleavage stage embryos

The justification of increased incidence of MZ twins after blastocyst transfer is one that prolonged culture leads to hardening of zona pellucida which forces inner cell mass to divide before time to make two fetal poles and second Changes in the culture media like absence of growth factors or cytokines and presence of high level free radicals can induce apoptosis leading to disruption of the inner cell mass at the time of hatching resulting in zygotic splitting.

3. Embryo culture conditions (culture media and time)
† Hardening of zona pellucida
† Apoptosis with changes in inner cell mass

4. Ovulation induction with gonadotrophins or clomiphene citrate

Ovarian stimulation may increase the number of available splitting-prone oocytes and consequently increase the risk of monozygotic twins also there is an evidence for Medication-induced structural alterations of zona pellucida

5. Inherited defects in zona pellucida like 
† Hardening of zona pellucida
† Failure or delay of cell-to-cell recognition and adhesion

So in a nutshell we should discuss the possibility of MZ twinning in cases where ICSI/AH/PGD is applied and also where blastocysts are transferred. There are reports that MZT chances increase in older oocytes and this tendency is inherited in some families (so ask for any twins in the house