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. 2016 Jan;33(1):19-26.
doi: 10.1007/s10815-015-0616-x. Epub 2015 Nov 18.

Clustering of monozygotic twinning in IVF

Denis A Vaughan  1 , Robin Ruthazer  2 , Alan S Penzias  3   4 , Errol R Norwitz  5 , Denny Sakkas  3
Affiliations

Clustering of monozygotic twinning in IVF

Denis A Vaughan et al. J Assist Reprod Genet. 2016 Jan.

Abstract

Purpose: The aim of this analysis was to study whether monozygotic twinning (MZT) events occur in clusters after IVF and, if so, to explore possible explanations for this clustering.

Methods: This is a retrospective cohort study carried out in a single, large university-affiliated reproductive medicine practice. Medical records of all patients who had undergone fresh IVF cycles, resulting in a viable clinical pregnancy, from Jan 2002 to Dec 2013 were reviewed. The incidence of MZT in 6-month intervals and the association with independent risk factors such as maternal age, extended embryo culture, PGD/intracytoplasmic sperm injection (ICSI)/assisted hatching performed were analyzed.

Results: Over the 12-year study period, 25,502 fresh IVF cycles were performed, resulting in 8598 clinical pregnancies. Ninety-five cycles (1.1 %) resulted in MZ twins. The percentage of MZT was >2 standard deviations (SD) higher than the overall percentage of MZT in 4 of the 24 6-month intervals. PGD, extended embryo culture (≥4 days), and more recent cycles (2005 or later) were independent risk factors for MZT. The use of multivariable logistic regression modeling to control for risk factors for MZT did not correct for this clustering effect, with both high-risk interval (clustering) and extended embryo culture remaining significant.

Conclusion: This study supports our hypothesis that MZT occurs in clusters and that this clustering effect could not be explained by demographics and cycle characteristics alone. Although we are unable to explain the clustering phenomenon, this study is important as it highlights high-risk intervals for MZT and opens the door to performing a more detailed investigation, to identify the mechanisms responsible for the spikes of MZT incidence.

Keywords: In vitro fertilization; Monozygotic twins; Risk factors; Trends.

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Figures

Fig. 1
Fig. 1
A U-chart displaying 6-month MZT rates over time with reference to standard deviation. High-risk intervals >2 SD are indicated by an asterisk
See this image and copyright information in PMC

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