title: The day of embryo transfer affects delivery rate, birth weights, female-to-male ratio, and monozygotic twin rate.
abstract: OBJECTIVE
  To compare the reproductive outcomes between the transfer of cleavage-stage embryos and blastocysts in two different age groups of patients. The reproductive capacity of women decreases by age. This decrease in capacity is directly related to a lower ovarian reserve and errors in the meiotic spindle of the oocyte, which increase chromosomal abnormalities and the formation of aneuploidy embryos with lower chances of implantation.
  
  
  METHODS
  A total of 1400 intracytoplasmic sperm injection cycles were analyzed. The study patients were divided into two age groups [aged < 36 years (Group I) and aged ≧ 36 years (Group II)]. The groups were subdivided according to the day of embryo transfer (ET)-Day 3 (ET3) and Day 5 (ET5).
  
  
  RESULTS
  In both age groups, transfer of blastocysts resulted in a higher clinical pregnancy rate and deliveries. An increased twin birth rate was observed in patients who were younger than 36 years on both transfer days compared with those who were older than 36 years of age. There was an elevated percentage of newborn males on ET5 in both age groups. Monozygotic twinning (MZT) rate was observed only among younger patients (<36 years of age), specifically on ET5 compared with ET3. There was no significant difference in the mean birth weight of singleton and twins between the ET3 and ET5 subgroups in the younger group of patients except for the triplets who were significantly heavier in the ET5 group compared with the older group (≧36 years of age) where significant difference was found only on the mean birth weight of singleton.
  
  
  CONCLUSIONS
  The study suggests that if a blastocyst can be obtained in patients of advanced age (≧36 years), it improves their baby take-home rates. Younger patients (aged < 36 years) should undergo elective single blastocyst transfers to reduce multiple pregnancy rates.
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia. Electronic address: vsotiroska@yahoo.com.
authors.forename: Valentina
authors.initials: V
authors.lastname: Sotiroska
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Zorancho
authors.initials: Z
authors.lastname: Petanovski
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Gligor
authors.initials: G
authors.lastname: Dimitrov
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Makjuli
authors.initials: M
authors.lastname: Hadji-Lega
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Damjan
authors.initials: D
authors.lastname: Shushleski
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Stefan
authors.initials: S
authors.lastname: Saltirovski
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Matevski
authors.affiliation: Center for Assisted Reproduction and IVF Fertilization, General Private Hospital-Remedika, Skopje, Macedonia.
authors.forename: Simona
authors.initials: S
authors.lastname: Shenbakar
authors.affiliation: Institute for Biology, Faculty for Natural Science and Mathematics, Saints Cyril and Methodius University, Skopje, Macedonia.
authors.forename: Sasho
authors.initials: S
authors.lastname: Panov
authors.affiliation: Reproductive Centre, Women's Clinic, Academic Hospital, Uppsala, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Johansson
mesh_terms: D000328:Adult; D001723:Birth Rate; D001724:Birth Weight; D001755:Blastocyst; D002970:Cleavage Stage, Ovum; D036861:Delivery, Obstetric; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies; D017678:Sex Distribution; D020554:Sperm Injections, Intracytoplasmic; D038522:Twinning, Monozygotic
keywords: age; blastocyst; delivery rate; embryo transfer; monozygotic twinning rate