Deliveries of normal healthy babies from embryos originating from oocytes showing the presence of smooth endoplasmic reticulum aggregates.

STUDY QUESTION: Should oocytes showing the presence of smooth endoplasmic reticulum aggregates (SER) be considered for embryo transfer?

SUMMARY ANSWER: The present study shows that embryos derived from metaphase II oocyte with visible SER (SER+MII) have the capacity to develop normally and may lead to newborns with no major malformations.

WHAT IS KNOWN ALREADY: It has been reported that the presence of SER in the cytoplasm of oocytes has a negative impact on embryo development, and is associated with a decreased clinical outcome and an increased risk of congenital anomalies. Therefore, it has been recommended that embryos derived from SER-positive oocytes should not be transferred.

STUDY DESIGN, SIZE, DURATION: Consecutive ICSI cycles with at least one SER+MII oocyte were retrospectively analyzed regarding embryological and pregnancy outcome and compared with ICSI cycles showing only oocytes without SER (SER-MII).

PARTICIPANTS/MATERIALS, SETTING, METHODS: In total, 394 SER-positive (SER+) cycles and 6845 SER-negative (SER-) cycles were analyzed. The Student's t-test, one-way analysis of variance test and χ(2) test were used for statistical analysis. P value of <0.05 was considered statistically significant.

MAIN RESULTS AND THE ROLE OF CHANCE: Comparable fertilization rates were observed in SER+ (76.2%) and SER- (73.5%) cycles. In case of blastocyst culture, the cycle efficiency was lower in SER+ than in SER- cycles (mean 42.2 versus 62.8%, P < 0.001). The pregnancy and clinical pregnancy (CP) rates per embryo transfer (ET) were comparable for SER+ and SER- cycles (37.6 versus 37.8% and 33.0 versus 32.4%, respectively). In the SER+ cycles, the fertilization rates of SER+MII and SER-MII (72.9 versus 77.0%), as well as the capacity to develop into good-quality embryos on Days 3 (62.3 versus 63.7%) and 5 (45.4 versus 47.4%), were similar. In the 364 SER+ cycles, the ETs were subdivided in: ET with only SER+MII (n = 31; 8.5%), ET with only SER-MII (n = 235; 64.5%) and ET with mixed SER+ and SER-MII (n = 98; 26.9%). The pregnancy (25.8, 37.4 and 41.8%, respectively) and CP rates (22.6, 32.4 and 37.9%, respectively) were not different between the three subgroups. Among the cycles with known outcome, there was no difference in the rate of major malformations between SER+ cycles (5.3%) and SER- cycles (2.1%). Moreover, no major malformations were reported from the live borns definitely originating from SER+MII embryos. In addition, three newborns, from single ET with frozen-thawed embryos originating from SER+MII oocytes, were delivered and presented no major malformation.

LIMITATIONS, REASONS FOR CAUTION: Taking into account the previous publications and our neonatal data, a follow-up of the children born after ET with embryos originating from SER+ cycles is encouraged.

WIDER IMPLICATION OF THE FINDINGS: More studies should be performed to investigate the origin and effect of SER aggregates on the molecular status of oocytes and embryos.

STUDY FUNDING/COMPETING INTEREST(S): No external funding was either sought or obtained for this study and there are no potential competing interests.

TRIAL REGISTRATION NUMBER: Not applicable.