Outcome assessments

The intermediate reproductive and pregnancy outcomes of ICSI treatment, including the number of normally fertilized embryos, number of cleaved embryos, number of good-quality embryos, number of day-3 available embryos, number of embryos cultured past day-3, number of blastocysts, number of available blastocysts, biochemical pregnancy, miscarriage, clinical pregnancy and live birth were abstracted from the medical records. The perinatal outcomes, including delivery mode (natural labor or cesarean delivery), fetal sex (male or female), gestational age, and birth weight were obtained from telephone interviews after delivery. The abovementioned outcomes were also calculated for in vivo matured and R-IVM oocytes separately in women undergoing ICSI with R-IVM group.

Normal fertilization was defined as the presence of two pronuclei (2PN). The normal fertilization rate was defined as the number of 2PN oocytes divided by the number of MII oocytes. The cleavage rate was defined as the number of cleaved embryos developed from 2PN oocytes divided by the number of 2PN oocytes. Cleavage embryonic development was evaluated using Veeck systems. Good-quality embryos were defined as normally fertilized embryos with 7-9 cells, fragmentation less than 10%, and without multinucleation on day-3. The good-quality embryo rate was defined as the number of good-quality embryos divided by the number of cleaved embryos. The available embryo rate was defined as the number of day-3 available embryos divided by the number of oocytes retrieved. The blastocysts were evaluated using the Gardner system. On Day 5 or 6, blastocysts with ≥3BC grade were considered to be available for cryopreservation. The blastocyst formation rate was defined as the blastocysts divided by the number of embryos cultured past day-3. The available blastocyst rate was defined as the number of blastocysts for cryopreservation divided by the number of embryos cultured past day-3. Biochemical pregnancy was defined as a positive result of HCG measurement without ultrasonographic visualization of clinical pregnancy. Clinical pregnancy was defined as the presence of a gestational sac with fetal heart activity by ultrasound 28 days after embryo transfer. Miscarriage was defined as pregnancy loss before gestational week 28. Live birth (LB) was defined as the delivery of a live newborn after gestational week 28. Cumulative LBR was defined as the chance of having LB after fresh and frozen transfers of embryos derived from one ICSI cycle. Preterm birth was defined as delivery at <37 weeks of gestation. Low birth weight was defined as child birth weight <2500g. Macrosomia was defined as child birth weight >4000g.