SEX SELECTION MAY BE INADVERTENTLY PERFORMED IN IN-VITRO FERTILIZATION-EMBRYO TRANSFER PROGRAMS

The present study aims to ascertain whether sex selection may be inadv ertently performed in human in-vitro fertilization (IVF) and embryo tr ansfer (IVF-embryo transfer) programmes when selecting for high qualit y embryos (those with the fastest cleaving rates and/or the best morph ology) at the fresh transfer cycle, All patients entering into the stu dy were treated with gonadotrophins after pituitary suppression with g onadotrophin-releasing hormone agonists (GnRHa) and had intrauterine e mbryo transfer on day 2 post-insemination, These patients were retrosp ectively divided into three groups according to whether the difference in mean number of cells between embryos transferred and all embryos a vailable for transfer in a given cycle was less than (negative selecti on), equal to (no selection) or greater (positive selection) than zero , In cycles resulting in singleton births, the sex ratio of the result ing babies was significantly (P less than or equal to 0.005) shifted t oward the female (88.8%) and to the male (90.0%) in the negative and p ositive selection groups respectively, No shift in sex ratio was obser ved in cycles resulting in multiple births, Maternal age was another i ndependent factor affecting sex ratio at birth, Sex ratio was signific antly (P less than or equal to 0.05) skewed in favour of males (62.7%) and females (71.4%) in women <35 and greater than or equal to 35 year s of age respectively, Maternal age, number of embryos transferred and the event of selecting or not selecting the slowest cleaving embryos for transfer were entered automatically in a three-group discriminant model for distinguishing cycles resulting in only boys, both boys and girls, and only girls, These data suggest that (i) sex selection may b e inadvertently performed in IVF-embryo transfer programmes when selec ting for high quality embryos at the fresh transfer cycles; (ii) human endometria may be favourable, indifferent or hostile to either fast c leaving or slow cleaving embryos depending on maternal age; and (iii) 'natural' sex selection may be performed for social, psychological or medical reasons.