A recent study posted on the preprint server Research Square* under review for publication in a Nature Portfolio journal reports that coronavirus disease 2019 (COVID-19) vaccines administered through the first follicular phase of the menstrual cycle can temporarily increase the duration of the menstrual cycle.

Study: Timing of COVID19 vaccination drives menstrual cycle changes. Image Credit: Trismegist san / Shutterstock.com

*Necessary notice: Research Square publishes preliminary scientific reports that aren’t peer-reviewed and, due to this fact, shouldn’t be thought to be conclusive, guide clinical practice/health-related behavior, or treated as established information.

Background

Menstrual health, including menstrual cycle and menses duration, regularity, and volume, is a vital indicator of general health and fertility in women. Nearly half of the feminine population, which accounts for roughly 26% of the worldwide population, are of reproductive age. On average, a girl menstruates for a duration of seven years of her life.

Despite the numerous association with overall quality of life and fertility, menstrual health outcomes aren’t routinely investigated in clinical trials. In truth, only a small variety of studies conducted through the COVID-19 pandemic have reported temporary menstrual disturbances following COVID-19 vaccination. This may be resulting from the results of vaccine-related immune responses on the hypothalamic-pituitary-ovarian (HPO) axis, which regulates menstrual cycle timing.

The menstrual cycle comprises the follicular and luteal phases. Throughout the follicular phase, which is the primary a part of the menstrual cycle, the ovary prepares for and executes ovulation. The follicular phase primarily determines the menstrual cycle length, whereas the luteal phase starts after ovulation, during which the uterus prepares for a possible pregnancy.

In the present study, scientists investigate the association between COVID-19 vaccination timing and its role in affecting the duration of the menstrual cycle.

Concerning the study

The present study analyzed menstrual cycle tracking data collected from 19,497 reproductive-aged women who used a digital fertility-awareness application called “Natural Cycles.” The information was used as a proxy to find out the timing of the follicular and luteal phases.

The duration of the menstrual cycle was compared between 9,279 and 5,532 women who were vaccinated either during either the follicular or luteal phases, respectively. A complete of 4,686 unvaccinated women were also included within the study as controls.

COVID-19 vaccination during follicular phase extends menstrual cycle duration

A complete of 19,497 participants from america, Canada, continental Europe, and the UK were included within the study. About 80% of the study cohort were under the age of 35 years, with about 64% having received a messenger ribonucleic acid (mRNA)-based COVID-19 vaccine.

As in comparison with vaccinated study participants, unvaccinated women were more prone to be under the age of 25 years, have a low educational background, and be residents of america or Canada.

As in comparison with pre-vaccination menstrual cycle duration, the post-vaccination cycle length increased by sooner or later in women who received the primary vaccine dose through the follicular phase. Comparatively, the cycle duration remained unchanged in those vaccinated through the luteal phase and unvaccinated individuals. Similar findings were observed for participants who received the second vaccine dose.

For each the primary and second vaccine doses, the proportion of participants experiencing a clinically significant increase within the duration of their menstrual cycle, which is reflected by a menstrual cycle duration exceeding eight days, was significantly higher in those vaccinated through the follicular phase as in comparison with those vaccinated through the luteal phase and unvaccinated controls.

Study significance

The impact of COVID-19 vaccination on menstrual cycle duration primarily depends upon the timing of vaccination. The present study reports that ladies vaccinated through the follicular phase may experience a rise within the duration of their menstrual cycle. Nevertheless, vaccination performed through the luteal phase was not found to affect menstrual cycle duration.

The HPO axis regulates the recruitment of the dominant follicle through the follicular phase. Vaccine-induced immune responses can modulate the activity of the HPO axis, thereby resulting in disruption of the timing of the luteinizing hormone surge and subsequent alteration within the timing of ovulation.

Thus, changes within the interaction between the immune and reproductive systems through the follicular phase resulting from vaccine-induced immune response may be accountable for the temporary alteration in menstrual cycle duration. For the reason that luteal phase length doesn’t rely on the HPO axis, vaccination performed during this phase has no effect on cycle duration.

*Necessary notice: Research Square publishes preliminary scientific reports that aren’t peer-reviewed and, due to this fact, shouldn’t be thought to be conclusive, guide clinical practice/health-related behavior, or treated as established information.