Objective: To compare pregnancy outcomes between pregnancies following day 2, day 3, and days 5/6 fresh embryo transfer (ET).
Methods: A retrospective cohort study including all pregnancies following fresh IVF/intracytoplasmic sperm injection (ICSI) ET cycles performed between January 2014 and December 2015 at Fertility and In Vitro Fertilization (IVF) Unit of the tertiary Soroka University Medical Center. The study groups consisted of 48, 72, 120, and 144 hours embryos. Pregnancies were confirmed by a serum beta-human chorionic gonadotropin measurement. Data regarding patients' medical history, infertility workup, fertility treatment characteristics, and outcome, as well as obstetrical outcome, were collected from patients' medical records and IVF Laboratory database. Multiple regression models were constructed to control for confounders. Patients who underwent fertility preservation treatment, cycles of oocyte donation or in vitro maturation oocytes, and cases of preimplantation genetic testing were excluded.
Results: A total of 534 pregnancies following fresh IVF/ICSI ET on day 2 (n = 189, 35.4%), day 3 (n = 200, 37.5%), and days 5 or 6 (n = 145, 27.2%) were included. Live birth rate demonstrated a linear association to the developmental stage at ET with the highest rates in blastocysts and gradually lower in day 3 and day 2 ET (79.2, 65.8, and 60.6%, respectively, p = .001). A positive linear association was also observed between ET age and clinical pregnancy rate (77.3, 87.5, and 90.3% for days 2, 3, and 5/6, respectively, p = .002), as well as with combined pregnancy complication rate (29, 37.3, and 43.3%, p = .026). However, using multivariate logistic regression model controlling for ET age, maternal age, smoking, obesity, initial HCG level and peak E2 level, live birth rate was comparable between the study groups regardless of ET age. Pregnancy complications were comparable between the groups; however, a composite pregnancy complications variable was higher in the blastocyst pregnancies compared to cleavage embryos pregnancies.
Conclusions: The common approach of blastocyst transfer, as high quality of the embryo, has not proven beneficial in terms of live birth rate. Moreover, cleavage stage embryos were not associated with adverse perinatal outcomes. The current data suggest maternal age has an independent effect on live birth.
Keywords: Blastocyst; cleavage stage; embryo transfer; pregnancy outcome.