Developmental potential of zona pellucida free oocytes obtained following mild in vitro fertilization

Zona pellucia–free eggs could be cultured until the blastocyst stage with efficacy similar to zona intact control eggs, without adversely affecting pregnancy rates and the neonatal outcome of resulting offspring.


Satoshi Ueno, M.Sc., Daniel Bodri, M.D., M.Sc., Ph.D., Kazuo Uchiyama, M.T., Tadashi Okimura, B.Sc., Takashi Okuno, M.D., Tamotsu Kobayashi, M.D., Keiichi Kato, M.D.

Volume 102, Issue 6, Pages 1602-1607



To determine the developmental potential of oocytes in which the zona pellucida was damaged and subsequently removed, producing “zona-free” (ZF) oocytes that were cultured until the blastocyst stage.


ZF eggs from cycles with more than one oocytes retrieved (n = 97) were compared with zona-intact (ZI) oocytes originating from the same patient.


Private infertility clinic.


Infertile patients (n = 135) undergoing minimal ovarian stimulation or natural-cycle in vitro fertilization treatment during 2010–2012.


ZF oocytes undergoing intracytoplasmic sperm injection (ICSI) fertilization, blastocyst culture, elective vitrification, and subsequent single vitrified-thawed blastocyst transfer (SVBT).

Main Outcome Measure(s):

Rate of fertilization, cleavage, and blastocyst development. Live birth rate and neonatal outcome in subsequent SVBT cycles.


There were no significant differences in fertilization (77% vs. 77%), cleavage (75% vs. 75%), or blastocyst development rates (39% vs. 32%) between the internally controlled ZF and ZI groups, respectively. Survival after thawing (90% vs. 100%) and live birth rates (37% vs. 36%) per thawed blastocyst were also similar. Newborns originating from all ZF and ZI oocytes had a similar gestational age at delivery (38.3 ± 3.7 wk vs. 39.5 ± 1.5 wk) and birth weight (3,115 ± 946 g vs. 3,010 ± 441 g).


Our retrospective comparative study suggests that ZF eggs could be as successfully fertilized and cultured until the blastocyst stage as ZI control eggs without adversely affecting subsequent pregnancy rates and basic neonatal outcome.

Read the full text at: