Obstetric and perinatal outcomes after either fresh or thawed frozen embryo transfer: an analysis of 112,432 singleton pregnancies recorded in the Human Fertilisation and Embryology Authority anonymized dataset.
OBJECTIVE
To explore obstetric and perinatal outcomes in singleton pregnancies occurring as a result of fresh and thawed frozen embryo transfer using anonymized Human Fertilisation and Embryology Authority data.


METHODS
Retrospective cohort study.


METHODS
Not applicable.


METHODS
Singleton births after IVF/intracytoplasmic sperm injection cycles in the United Kingdom (1991-2011).


METHODS
A total of 112,432 cycles (95,911 fresh and 16,521 frozen) were analyzed using multivariate logistic regression to explore associations between type of embryo transferred (frozen vs. fresh) and obstetric and perinatal outcomes. Relative risks (RRs) and their 99.5% confidence intervals (CIs) were calculated using Stata 14 MP, adjusting for potential confounders.


METHODS
Birth weight.


RESULTS
The adjusted RR (99.5% CI) of low birth weight [0.73 (0.66-0.80)] and very low birth weight [0.78 (0.63-0.96)] were all lower after frozen embryo transfer; however, RR of having a high birth weight baby was higher [1.64 (1.53-1.76)]. There was no difference in RR of preterm birth [0.96 (0.88-1.03)], very preterm birth [0.86 (0.70-1.05)], and congenital anomalies [0.86 (0.73-1.01)].


CONCLUSIONS
The findings of low birth and very low birth weight after thawed frozen embryo transfer are consistent with the literature and provide reassurance regarding the outcome of pregnancies after frozen embryo transfers. However, they highlight the possibility of high birth weight in these babies. Because these results are based on observational data, further evidence from randomized, controlled trials is needed before elective cryopreservation of all embryos is practiced in preference to the current practice of transfer of fresh embryos.
National Health Service Grampian, Aberdeen, United Kingdom. Electronic address: abha.maheshwari@abdn.ac.uk.
Abha
A
Maheshwari
Institute of Applied Health Sciences, University of Aberdeen, Aberdeen, United Kingdom.
Edwin Amalraj
EA
Raja
Institute of Applied Health Sciences, University of Aberdeen, Aberdeen, United Kingdom.
Siladitya
S
Bhattacharya
D000293:Adolescent; D000328:Adult; D001724:Birth Weight; D000013:Congenital Abnormalities / Q000209:etiology; D015925:Cryopreservation; D016208:Databases, Factual; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000009:adverse effects; D005260:Female; D005298:Fertility; D005307:Fertilization in Vitro / Q000009:adverse effects; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight; D019102:Infant, Very Low Birth Weight; D007246:Infertility / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D050498:Live Birth; D016015:Logistic Models; D015999:Multivariate Analysis; D016017:Odds Ratio; D011247:Pregnancy; D018873:Pregnancy Rate; D047928:Premature Birth / Q000209:etiology; D012189:Retrospective Studies; D012307:Risk Factors; D020554:Sperm Injections, Intracytoplasmic; D013997:Time Factors; D016896:Treatment Outcome; D006113:United Kingdom; D055815:Young Adult
Frozen replacement cycles; ICSI; IVF; obstetric outcomes; perinatal outcomes