Abstract
To determine if prolonged time in embryo culture has an effect on the rate, sex ratio, and perinatal outcomes of monozygotic twins (MZT) following either cleavage stage or blastocyst embryo transfer after assisted conception. This is a retrospective study of 2,316 consecutive clinical pregnancies resulting from cleavage stage transfer (CT) and blastocyst transfer (BT). Criteria examined included (i) incidences (ii) sex ratios (iii) gestational age and birth weight; (iv) perinatal outcomes of these pregnancies from cleavage stage and blastocyst transfer procedures. Monozygotic twin pregnancies were identified by (i) presence of a gestational sac containing more than one fetal pole with cardiac activity, (ii) the number of gestational sacs or fetal hearts exceeds the number of embryos transferred and (iii) twin pregnancies following a single embryo transfer. Overall the incidence of twinning was 1.64% (38 out of 2,316 pregnancies). The frequency of twinning was 2.3 × higher following BT (18 out of 649) compared to CT (20 out of 1,667). IVF techniques skewed the sex ratio in favour of males while ICSI significantly favoured females. There was no statistically significant difference between transfer type and gestational age, birth weight and perinatal outcome. All pregnancies resulted in the birth of 86 infants. In our experience, BT more than doubles the chances of conceiving a monozygotic twin pregnancy, however IVF techniques lead to a greater likelihood of male birth(s) if twins are conceived. Appropriate pre-conception counselling should be given to advise the potential risks associated with both types of transfer as well as using alternative methods such as single embryo transfer to reduce the risk of multiple gestations.
Highlights
The manner by which division of a single fertilized embryo during the premature phases of embryonic development (monozygotic twinning (MZT)) leads to the formation of two separate individuals is dependent on the timing of embryonic cleavage after conception [1]
In the blastocyst group ICSI did not increase the incidence of monozygotic twins (MZT) either (11 of 1,314, 0.83% for ICSI and 7 of 1,002, 0.69% for IVF). (iii) Sex ratio: By comparing sex ratios between IVF and ICSI pregnancies, we identified that IVF skewed the sex ratio in favour of males
MZT births developed in both groups by using ICSI and IVF were comparable and suggestive that zona manipulating techniques do not have any effect on the incidence
Summary
The manner by which division of a single fertilized embryo during the premature phases of embryonic development (monozygotic twinning (MZT)) leads to the formation of two separate individuals is dependent on the timing of embryonic cleavage after conception [1]. The clinical consequences of multiple pregnancies play an important role in society in part because of the economic burdens but due to both maternal and fetal complications that can arise. The purpose of this study was to test the hypothesis that there is a differential rate of twinning, a differential sex ratio, different gestational ages at birth, different birth weights and different clinical outcomes of MZT depending on whether embryos were transferred at cleavage or blastocyst stage
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