Delay of embryo transfer to day 5 results in decreased initial serum β-human chorionic gonadotropin levels

Objective: To investigate the impact of delaying the transfer of in vitro fertilized embryos to day 5 on embryo development by comparing serum β-hCG levels in pregnancies established after day 3 embryo transfers and those after day 5 blastocyst transfers at equivalent time intervals after fertilization. Design: A retrospective analysis. Setting: Assisted reproductive technology center in an academic research environment. Patient(s): Women who had an embryo transfer procedure performed after in vitro fertilization (IVF) at Northwestern University's IVF Program between January 1999 and December 2001 were included in this study. Intervention(s): Embryo transfer was performed either on day 3 or day 5 after oocyte retrieval for IVF (day 0), depending on the availability of good-quality embryos on day 3. Main Outcome Measure(s): Serum β-hCG concentrations determined 13 and 15 days after fertilization in pregnancies established by transferring cleavage-stage embryos on day 3 or blastocysts on day 5. Result(s): In singleton pregnancies, serum β-hCG concentrations were 75 ± 54 (mean ± SD, n = 203) or 62 ± 41 (n = 109) IU/mL after day 3 or day 5 transfers, respectively. In twin pregnancies, the β-hCG concentrations were 162 ± 105 (n = 52) or 109 ± 55 (n = 49) after day 3 or day 5 transfers, respectively. The percentage increases in β-hCG concentrations between the first and second measurements were similar in the two groups (day 3: 144 ± 109, day 5: 142 ± 63, not statistically significant). Conclusion(s): Initial β-hCG concentrations in pregnancies resulting from day 5 transfers were lower than those from day 3 transfers when assessed at equivalent intervals from fertilization. This suggests that embryo development or implantation may be impaired by the additional 2 days in culture.