Impact of blastocyst transfer on offspring sex ratio and the monozygotic twinning rate: a systematic review and meta-analysis.
OBJECTIVE
To determine the sex ratio and risk of monozygotic twinning (MZT) after blastocyst transfer compared with cleavage-stage embryo transfer (ET) in fresh IVF cycles.


METHODS
Systematic review and meta-analysis.


METHODS
University hospital center for reproductive medicine and IVF.


METHODS
Results of all reports from January 1995 to November 2007 with women undergoing nondonor fresh IVF. The sex ratio of 2,587 offspring and MZT rate in 40,917 cycles were included.


METHODS
Cleavage or blastocyst stage for embryo transfer.


METHODS
Sex ratio and rate of MZT.


RESULTS
A meta-analysis was performed using four studies for sex ratio and nine studies for MZT. The results of the meta-analysis using a fixed effect model demonstrated a higher male-female ratio after blastocyst transfer compared with cleavage-stage ET (odds ratio [OR] 1.29, 95% confidence interval [CI] 1.10-1.51), and this difference was statistically significant. The risk of MZT after blastocyst transfer was significantly higher compared with cleavage-stage ET (OR 3.04, 95% CI 1.54-6.01).


CONCLUSIONS
The combined data presented in this meta-analysis suggest that blastocyst transfer appears to be associated with a sex ratio skewed in favor of males and an increased risk of MZT. The clinicians should provide this information to their infertility patients awaiting blastocyst transfer.
Chang
Hye Jin
HJ
Department of Obstetrics and Gynecology, Seoul National University Bundang Hospital, Seongnam, South Korea.
Lee
Jung Ryeol
JR
Jee
Byung Chul
BC
Suh
Chang Suk
CS
Kim
Seok Hyun
SH
D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods; D006801:Humans; D007231:Infant, Newborn; D010062:Ovulation Induction / Q000379:methods; D011247:Pregnancy; D011256:Pregnancy Outcome; D016032:Randomized Controlled Trials as Topic / Q000379:methods; D012189:Retrospective Studies; D012744:Sex Ratio; D014430:Twins, Monozygotic