The effect on human sex ratio at birth by assisted reproductive technology (ART) procedures – an assessment of babies born following single embryo transfers, Australia and New Zealand, 2002–2006

Abstract

Objective To assess the effect on the human sex ratio at birth by assisted reproductive technology (ART) procedures.Design Retrospective population-based study.Setting Fertility clinics in Australia and New Zealand.Population The study included 13 368 babies by 13 165 women who had a single embryo transfer (SET) between 2002 and 2006.Methods Logistic regression was used to model the effect on the sex ratio at birth of ART characteristics [in vitro fertilisation (IVF) or intracytoplasmic sperm insemination (ICSI) SET, cleavage-stage or blastocyst SET, and fresh or thawed SET] and biological characteristics (woman's and partner's age and cause of infertility).Main outcome measures Proportion of male births. ResultsThe crude sex ratio at birth was 51.3%. Individual ART procedures had a significant effect on the sex ratio at birth. More males were born following IVF SET (53.0%) than ICSI SET (50.0%), and following blastocyst SET (54.1%) than cleavage-stage SET (49.9%). For a specific ART regimen, IVF blastocyst SET produced more males (56.1%) and ICSI cleavage-stage SET produced fewer males (48.7%).Conclusions The change in the sex ratio at birth of SET babies is associated with the ART regimen. The mechanism of these effects remains unclear. Fertility clinics and patients should be aware of the bias in the sex ratio at birth when using ART procedures.Keywords ART births, blastocyst, cleavage-stage embryo, ICSI, IVF, logistic regression, sex ratio at birth, single embryo transfer.Please cite this paper as: Dean J, Chapman M, Sullivan E. The effect on human sex ratio at birth by assisted reproductive technology (ART) procedures -an assessment of babies born following single embryo

Effects of assisted reproductive technologies on human sex ratio at birth

“…The apparent lack of risk of SSR alteration under IUI may reflect a genuine lack of effect of it could be due to the relatively small sample size recorded for IUI. Overall, these results are qualitatively consistent with previous observations of lower SSR after ICSI and higher SSR following IVF (8,(27)(28)(29)(30)(31).…”

“…For both ICSI and IVF, transferring embryos at a later stage of development (days 4-7) result in sex ratios up to 6% higher than after early transfer (days 1-3); this also accords with prior reports (8,10,30,32). It is also notable that single embryo transfer at the blastocyst stage results in significantly higher SSR (RR= 1.056, C.I.…”

“…We used backward elimination procedures and aggregation of factor levels to obtain the parsimonious 'minimal adequate model' by model simplification (8,(23)(24)(25). We report the percentage of deviance explained (%Dev) as an approximate analogue of r 2 .…”

“…In contrast, the secondary sex ratio, SSR, which may be defined as the proportion of live-born males out of all live births (13), is straightforward to assess and it is the SSR that most population censuses report in public databases (14)(15)(16). At reproductive age, sex ratio bias has the potential to generate substantial public health concerns (8,12,17), leading, for instance, to increased socially disruptive behaviour, transmission of sexually transmitted diseases and mental health problems (18)(19)(20)(21). …”

“…Not only do these three ART methods differ technically, they may differentially affect the sex ratio at birth (8)(9)(10)(11), with a general tendency for more males being produced compared to among naturally born offspring. The sex ratio at conception (primary sex ratio), defined according to the numbers of oocytes fertilized by X-or Y-bearing spermatozoa, is difficult to assess (12) and is thus usually unknown.…”