Iris de Nie

62 C H A P T E R 4 problems, which might have been underestimated in the retrospective cohort study. 96 When assessing the influence of these factors on the different semen parameters, none of the characteristics were able to explain the overall reduced semen quality in our cohort. Although drinking alcohol was associated with having a normal semen volume, sperm concentration, total sperm number and total motile sperm count, both the percentage of current drinkers in our cohort and the consumed units of alcohol per week, are lower than in the general population of similar age. 74 In this study we collected detailed data on habitual behavior more typically observed in transgender women. Many transgender women socially transition before starting medical treatment, and combined with the long waiting period for genital GAS, transgender women may feel the need to hide their external genitalia in order to express themselves more feminine by wearing tight-fitting clothes. However, until now it remained unclear how often tucking is performed by transgender women and what the consequences are. In our cohort, 14.1% of transgender women reported to perform tucking sometimes whereas 8.9% does it often. A study from 1985 assessed the influence of tucking in a cohort of cisgender men and observed the most dramatic decline in TMSC with a drop of 98% after more than 6 consecutive months of daily tucking. 89 This is in line with our observation that extensive tucking is associated with a low TMSC in transgender women (OR 7.95, 95% CI 1.66-37.99) and confirms the significant negative influence on semen quality. Another way to hide the external genitalia is wearing tight undergarment which may increase scrotal temperatures. The scrotal temperature is regulated by blood flow and the position of the testicles - towards and away from the body - through a collaboration between the cremaster muscle and the dartos muscle. Wearing tight undergarment may disrupt this system. Half of the transgender women in this study reported to regularly wear female underwear, stockings or special transgender underwear to press the genitals tight against the body. In cisgender men several studies have been conducted to evaluate the influence of tight undergarment on semen quality with varying results. 91,97,98 In our cohort, we found a negative impact of always wearing tight undergarment on TMSC, which is similar to what was observed in two other studies on this subject. 91,97 However, the odds ratio was slightly lower for the corrected model (OR 2.79, IQR 0.92-8.43) than for the crude analysis (OR 3.06, IQR 1.11-8.49). Lastly, we assessed ejaculation frequency in transgender women and hypothesized that it might be low due to genital dysphoria and hereby impair progressive motility. Indeed, when comparing those with the lowest ejaculation frequency with those with an average ejaculation frequency in our cohort, a negative impact on progressive motility was observed. However, no association with TMSC was found. Previously conducted studies in cisgender men suggest that daily ejaculation, resulting in a short abstinence time, may cause a decline in semen volume and sperm concentration but at the same time improves progressive motility. 99,100 Reversely, studies assessing the effect of abstaining from ejaculation for 11-21 days showed a significant decrease in the percentage progressive motility and normal morphology but an increase in semen volume and sperm