Hum. Reprod. Advance Access originally published online on April 27, 2008
Human Reproduction 2008 23(7):1644-1653; doi:10.1093/humrep/den150
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Factors affecting low birthweight after assisted reproduction technology: difference between transfer of fresh and cryopreserved embryos suggests an adverse effect of oocyte collection
1 Department of Obstetrics and Gynaecology, University of Melbourne, Melbourne, Australia 2 Melbourne IVF Reproductive Services, The Royal Women's Hospital, 283 Cardigan Street Carlton, Melbourne, Australia 3 Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia
4 Correspondence address. Tel: +61-3-9344-2130; Fax: +61-3-9347-1761; E-mail: g.baker{at}unimelb.edu.au
BACKGROUND: Data show that differences exist in the birthweight of singletons after frozen embryo transfer (FET) compared with fresh transfer or gamete intra-Fallopian transfer (GIFT). Factors associated with low birthweight (LBW) after assisted reproduction technology (ART) were studied.
METHODS: Birthweight, distribution of birthweight, z-score, LBW (<2500 g), gestation and percentage preterm (<37 weeks) for singleton births >19 weeks gestation, conceived by ART or non-ART treatments (ovulation induction and artificial insemination) between 1978 and 2005 were analysed for one large Australian clinic.
RESULTS: For first births, the mean birthweight was significantly (P < 0.005) lower, and LBW and preterm birth more frequent for GIFT (mean = 3133 g, SD = 549, n = 109, LBW = 10.9% and preterm = 10.0%), IVF (3166, 676, 1615, 11.7, 12.5) and ICSI (3206, 697, 1472, 11.5, 11.9) than for FET (3352, 615, 2383, 6.5, 9.2) and non-ART conceptions (3341, 634, 940, 7.1, 8.6). Regression modelling showed ART treatment before 1993 and fresh embryo transfer were negatively related to birthweight after including other covariates: gestation, male sex, parity, birth defects, Caesarean section, perinatal death and socio-economic status.
CONCLUSIONS: Birthweights were lower and LBW rates higher after GIFT or fresh embryo transfer than after FET. Results for FET were similar to those for non-ART conceptions. This suggests IVF and ICSI laboratory procedures affecting the embryos are not causal but other factors operating in the woman, perhaps associated with oocyte collection itself, which affect endometrial receptivity, implantation or early pregnancy, may be responsible for LBW with ART.
Key words: assisted reproduction technology/low birthweight/oocyte collection
Submitted on November 29, 2007; resubmitted on March 14, 2008; accepted on March 29, 2008.