OBJECTIVE: To investigate the impact of delaying the transfer of in vitro fertilized embryos to day 5 on embryo development by comparing serum beta-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. @entity1 (S): @entity1 who had an embryo transfer procedure performed after @entity52 ( @entity52 ) at Northwestern University's @entity52 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 @entity52 (day 0), depending on the availability of good-quality embryos on day 3. MAIN OUTCOME MEASURE(S): Serum beta-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 beta-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 beta-hCG concentrations were 162 +/- 105 (n = 52) or 109 +/- 55 (n = 49) after day 3 or day 5 transfers, respectively. The percentage increases in beta-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 beta-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.

Delay of embryo transfer to day 5 results in decreased initial serum beta- XXXX chorionic gonadotropin levels.

@entity1 :: ('9606', 'Species') :: ['PATIENT', 'Women'] @entity52 :: ('MESH:C566179', 'Disease') :: ['IVF', 'in vitro fertilization']
@entity1 :: (9606,Species) :: ['human']
