Some embryos derived from 1PN zygotes after conventional IVF procedures (cIVF-1PN) have been known to be diploid and have the potential to develop into healthy babies. In contrast, most embryos derived from 1PN zygotes after ICSI procedures (ICSI-1PN) have been reported to contain abnormal chromosome configurations. In this study, we analyze the clinical outcomes of cIVF-1PN and ICSI-1PN and investigate why ICSI-1PN zytotes failed to produce pregnancy.
A retrospective study involving 7497 frozen-thawed single blastocyst transfers. All patients received HRT and the study spanned from January 2011 to December 2014. Time-lapse observations were made on 79 1PN zygotes from January 2013 to February 2015.
Clinical pregnancy rates, miscarriage rates, live birth rates and malformation rates resulting from blastocysts derived from cIVF-1PN and ICSI-1PN were compared with blastocysts derived from cIVF-2PN and ICSI-2PN. Blastocysts derived from 1PN zygotes were transferred when there were no embryos derived from 2PN zygotes. Among 79 1PN zygotes, which were observed by a time-lapse system, the size of the single pronucleus from 40 ICSI-1PN zygotes were compared with those from 39 cIVF-1PN zygotes immediately before the breakdown of their pronuclear membranes.
A total of 7497 frozen-thawed single blastocyst transfers resulted in 3058 (40.8%) clinical pregnancies. Clinical pregnancy rates in cIVF-1PN, cIVF-2PN, ICSI-1PN, ICSI-2PN were 36.1% (26/72), 42.1% (2244/5332), 0% (0/20), 37.6% (814/2165) respectively. Among the 26 pregnancies derived from cIVF-1PN, 21 babies were born, 4 women miscarried and 1 case lost contact. A minor malformation (pneumothorax) was reported in 1 baby among the 21 postpartum babies. Among the 2244 pregnancies derived from cIVF-2PN, 1681 babies were born, 528 women miscarried and 35 cases lost contact. Malformations were reported in 30 babies among the 1681 postpartum babies. There were no statistical differences in clinical pregnancy rates, miscarriage rates, live birth rates and malformation rates between cIVF-1PN and cIVF-2PN. In contrast, the pregnancy rate from ICSI-1PN zygotes was zero, which was significantly lower than that in ICSI-2PN. The average size of ICSI-1PN was 666.4µm2 (±105.2) and was significantly less than that of cIVF-1PN 720.8µm2 (±114.4) (p=0.028). Student’s t-test or the chi-square test was used for statistical analyses where appropriate.
Zygotes derived from ICSI-1PN produced blastocysts but no pregnancies, while healthy babies were born from cIVF-1PN zygotes. There was no statistical difference in pregnancy rates between blastocysts derived from cIVF-1PN and cIVF-2PN. The smaller size of single pronuclei after ICSI compared with single pronuclei formed after IVF may be related to the disruption of microfilaments within the ooplasm caused by the penetrating micropipette.