Israel Medical Association Journal

Background: While the ratio of male to female births (sex-ratio at birth [SRB]) in humans is remarkably stable on the population level, there are many families with multiple same-sex offspring.

Objectives: To identify a putative sub-population with skewed SRB and explore potential factors affecting the SRB.

Methods: A retrospective cohort study including 66,054 families with up to nine same-sex offspring evaluated between 2003 and 2015 at Hadassah-Hebrew University Medical Center. Outcome measures were observed prevalence and SRB of families with up to nine same-sex offspring in a single family. Analyses included the effect of parity, month and year of delivery, inter-delivery interval, and presence of a sequence of previous same-sex offspring on the SRB.

Results: The study comprised 193,411 live-born babies with SRB of 1.057 in favor of males. The proportion of SRB in families with up to nine same-sex offspring did not differ from the calculated presumed proportion. Furthermore, none of the tested factors (parity, month and year of delivery, inter-delivery interval, and the sequence of previous same-sex offspring) were significantly associated with SRB.

Conclusions: SRB was not associated with any of the tested demographic characteristics. We could not identify a skew in SRB even in families with up to nine consecutive same sex offspring. This finding suggests that in the majority of the population the chance of a male or female fetus in each pregnancy remains similar in every pregnancy, regardless of any of the tested variables.

Background: Studies suggest that global semen quality is declining, but the debate remains open owing to geographic variation.

Objectives: To evaluate temporal trends of sperm parameters – namely concentration, motility and total motile sperm count – in sperm donated during the period 1995–2009.

Methods: In a retrospective longitudinal cohort study we analyzed the sperm count and motility of 2182 semen samples provided on a weekly basis by 58 young, healthy, fertile, university-educated, paid donors.

Results: Despite the lowering of criteria for sperm parameters satisfactory for donation that were implemented in 2004, 38% of applicants for sperm donation are now rejected based on semen quality as compared to a third of applicants 10–15 years ago (P < 0.001). If the old strict criteria were in place 88% of candidates would be rejected today (P < 0.0001). Over the study period, the average sperm parameters dropped from a concentration of 106 ± 25 million spermatozoa/ml with 79% ± 4.3% motility to 68 ± 14 million/ml with 66% ± 4.5% motile sperm (P < 0.0001, P < 0.0001, respectively). The total motile sperm count per ejaculate also decreased, from 66.4 ± 18.2 million to 48.7 ± 12 million (P < 0.005). When the previous criteria were implemented for the analysis of the latest group of sperm donors, only 18% of donors had an acceptable sperm quality, with an average concentration of 87 ± 12 million spermatozoa/ml, 73% ± 2.6% motile sperm and total motile sperm count of 53.1 ± 3.8 million per ejaculate – still significantly lower than 15 years ago (P = 0.01, P = 0.003, P = 0.058 respectively).

Conclusions: The rapid deterioration of sperm quality among fertile semen donors is alarming and may lead to cessation of sperm donation programs.