REPRODUCTIVE PHYSIOLOGYAND DISEASE
Early maternal serum ß-human chorionic gonadotropin (ß-hCG) levels and sex-related growth difference of IVF embryos
Efrat Esh-Broder1 & Galia Oron1 & Weon-Young Son1 & Hananel Holzer1 &
Received: 6 April 2015 /Accepted: 24 July 2015 # Springer Science+Business Media New York 2015
Purpose Maternal serum ß-human chorionic gonadotropin (ß-hCG) represents the trophoblastic cell mass and is an indirect measurement of embryo development at early implantation stage. Studies in animals and human embryos detected sex-related growth differences (SRGD) in favour of male embryos during the pre-implantation period. The purpose of our study was to correlate SRGD and maternal serum ß-hCG at 16 days after embryo transfer.
Methods We retrospectively analysed all (fresh and frozen) non-donor, single embryo transfers (SET), elective and not elective, that were performed between December 2008 and
December 2013. We included ß-hCG values from day 16 after oocyte collection of pregnancies resulting in live birth. Neonatal gender was retrieved from patient files. Male and female embryos were further grouped to cleavage and blastocyst stage transfers. Regression analysis for confounding variables included maternal age, maternal body mass index (BMI), use of micromanipulation (ICSI), embryo quality (grade), assisted hatching, day of transfer and fresh or frozen embryo transfer.
Results Seven hundred eighty-six non-donor SETs resulted in live birth. After including only day 16 serum ß-hCG results, 525 SETs were analysed. Neonatal gender was available for 522 cases. Mean maternal serum ß-hCG levels were similar, 347±191 IU/L in the male newborn group and 371±200 IU/L in the female group. The difference between ß-hCG levels remained insignificant after adjusting for confounding variables.
Conclusions Early maternal ß-hCG levels after embryo transfers did not represent SRGD in our study.
Keywords ß-hCG . IVF . Embryo . Sex related . Sex-related growth difference
Sex-related growth differences (SRGD) have been extensively studied in animals and human fetuses. More than 50 years ago, it was recognized that male offspring have a higher average birth weight . This was thought to result from a more advanced developmental rate of male fetuses compared to females at different stages of pregnancy [2, 3]. The proposed mechanism of this phenomenon during pregnancy was suggested to be the effect of secreted androgens and male hormones.
The introduction of assisted reproductive technology (ART) enabled evaluation of early embryos. Data started to accumulate showing sex-related growth differences in the preimplantation period even before the differentiation of the gonads. Early studies in animals detected SRGD in favour of male embryos during the pre-implantation period, mainly in mouse , and bovine blastocyst embryos [5, 6]. The limiting factor with human embryo studies was the ethical issue of confirming the gender prior to embryo transfer. Therefore, human studies were limited to either the use of surplus embryos that were not transferred or to correlation between pretransfer embryo cell number and the gender detected after birth.
Pergament et al.  found that a higher cleavage stage embryo cell number increased the probability of a male
Capsule Early maternal ß-hCG levels after embryo transfers did not represent SRGD in our study. * Efrat Esh-Broder email@example.com 1 Department of Obstetrics and Gynecology, McGill University,
MUHC Reproductive Center, Royal Victoria Hospital, 687 av des
Pins West, Montreal, QC H3A 1A1, Canada
J Assist Reprod Genet
DOI 10.1007/s10815-015-0550-y offspring. Ray et al.  assessed surplus embryos’ cell number and metabolic requirements at different embryo stages and correlated with embryo gender using karyotype. They reported higher average number of cells for cleavage stage male embryos compared to female. The most pronounced difference occurred at days 4–6, with a non-significant difference on day 6. Dumoulin et al.  used surplus embryos to correlate developmental rate with embryo gender determined by fluorescent in situ hybridization (FISH). They found a higher number of cells in male blastocysts fertilized by ICSI.
Another indirect evidence of a more rapid male embryo development is an altered sex ratio in favour of males observed at birth for the IVF population. There is no evidence of bias in spermatogenesis or fertilization in favour of Y sperm cells . Therefore, a possible explanation is a rapid development of male embryos, leading to a bias in selection of male embryos for transfer .
It is unknown if SRGD at advanced stages of pregnancy is a continuation of that of the pre-implantation period or a completely separate phenomenon affected by a different mechanism. It is difficult to directly assess embryo developmental rate in the time frame between implantation and the sonographic detection of a fetal pole.
Maternal serum beta human chorionic gonadotropin (ßhCG) is a subunit of HCG dimer, secreted by the embryonic trophoblastic cells and represents the trophoblastic cell mass . It is not a direct measurement of embryonic growth but is one of the earliest methods to assess pregnancy progression and correlates well with pregnancy outcome as early as 2 weeks after embryo transfer [13–15]. Previous studies found the influence of fetal gender on maternal serum ß-hCG, and women carrying female fetus had higher ß-hCG levels than those with male fetus in late first, second and third trimesters of pregnancy. This is most probably related to the differences in the activity of the fetal hypothalamic-hypophyseal-gonadal axis. [16–19]. Yaron et al.  found higher levels of maternal serum ß-hCG in female fetus in pregnancies that resulted from the transfer of both single and multiple embryos in IVF patients.
In order to assess whether embryonic sex-related growth differences persist after the pre-implantation period stage, we evaluated maternal serum ß-hCG from single embryo transfers resulting in male and female neonates.