Female mammals are thought to be born with a finite number of eggs, and when these eggs are reduced or of lower quality, it is called reduced reproductive potential. Although stress is part of our daily lives, it is one of the causes of this. Now, researchers are delving into the effects of stress on ovarian reserves.

To do this, scientists have been exposing rats to terrified screams, white noise, or background sounds to study stress effects on fertility. Yes, that is right… screams… for 3 weeks – poor rats! This noise was delivered through a speaker 50 centimeters (19.7 inches) above their cage for 6 hours a day: 3 in the morning and 3 in the afternoon. Their results were published in the journal Endocrinology.

Screaming is not a normal stressor used in research, so why use it?  

The chronic unpredictable mild stress (CUMS) and restraint stress model are normally accepted for psychological stress studies in rodents, but some of the stressors that are normally used – like food deprivation or light cycle modifications – may cause problems that are not stress-linked.

The normal CUMS white noise stress option was also determined to be an insufficient stress pressure, and this led the researchers to use the novel scream method (the noise for which was "kindly provided by professor Chen Huang", as the authors note). This also highlights why you should not play screamo next to your pet rat’s cage if you want them to be happy.

Once the rats had been stressed enough, the researchers analyzed the effect on the sex hormones, the ability to get pregnant and give birth after mating, and the number and quality of eggs.

“We examined the effect of stress on ovarian reserve using a scream sound model in rats,” said Wenyan Xi, PhD, of the Second Affiliation Hospital of Xi’an Jiao Tong University in Xian, China, in a statement. “We found that female rats exposed to the scream sound had diminished ovarian reserve and decreased fertility.”

It was found that the screaming sound decreases estrogen (important for growth and reproductive development) and Anti-Mullerian (Made by the ovaries and helps form reproductive organs) hormone levels. The sound also lowered the number and quality of the eggs and resulted in smaller litters.

“Based on these findings, we suggest stress may be associated with diminished ovarian reserve,” Xi said. “It is important to determine an association between chronic stress and ovarian reserve because doing so may expand our appreciation of the limitations of current clinical interventions and provide valuable insight into the cause of diminished ovarian reserve.”