Scientists have discovered a way to pause the growth of human embryos in a potential medical breakthrough.

The team found that by reducing activity in particular certain chain of biological reactions involved in fetal growth, they were able to temporarily halt a fertilized embryo from implanting in the uterine wall until conditions were optimal.

By slowing down the production of a protein involved fetal growth, they were able temporarily halt the fertilized embryo from growing at its earliest stage - about a week after conception.  

The researchers were able to maintain the embryos in this dormant state for 18 days, after which they reversed the pause to resume normal growth.

Researchers said the technique could be used to increase the success of IVF by creating a bigger time window to assess embryo health and improve chances of implantation in the uterus.

Over 130 species of mammals - from bears to mice - have the ability to temporarily pauses embryo development in a process called embryonic diapause. 

It typically occurs during the blastocyst stage - when a fertilized egg has rapidly divided into a ball of cells called a blastocyst. This early phase of development begins roughly five or six days after fertilization.

A team of researchers from the Max Planck Institute in Berlin and the Institute of Molecular Biotechnology (IMBA) of the Austrian Academy of Sciences in Vienna has discovered a way to artificially trigger a diapause-like-state in human stem cells and blastoids, which are lab-grown blastocysts.

In both stem cells and blastoids, the researchers altered the activity of a particular chain of reactions, also known as a molecular cascade.

A molecular cascade is when the motion of one molecule triggers the motion of another, and so on. This initiates a cascading series of chemical reactions. 

It works similarly to a row of toppling dominoes, where each falling domino causes the next one to fall.

The pathway that the researchers targeted is called the mTOR signaling pathway. It regulates cell metabolism, growth, proliferation and survival, and also plays an important role in fetal growth and development.

When the researchers inhibited the mTOR signaling pathway, stem cells and blastoids entered a dormant state similar to diapause. 

The study's findings show that the ability to enter dormancy is active in human cells around the blastocyst stage, the researchers wrote in their report.

In addition, they found they were able to reverse this AFTER HOW LONG, allowing blastoids to resume normal development. 

And when they enhanced mTOR pathway activity, they found that embryo development sped up.

They published their study this month in the journal Cell.

This research has uncovered a new way to control the growth of human pregnancies. 

'Although we have lost the ability to naturally enter dormancy, these experiments suggest that we have nevertheless retained this inner ability and could eventually unleash it,' said study co-author Nicolas Rivron of the Institute of Molecular Biotechnology (IMBA) of the Austrian Academy of Sciences in Vienna, in a statement. 

Learning how to tap into this hidden ability within our cells could have major implications for reproductive health treatments like IVF.

'On the one hand, undergoing faster development is known to increase the success rate of in vitro fertilization, and enhancing mTOR activity could achieve this,' Rivron explained. 

'On the other hand, triggering a dormant state during an IVF procedure could provide a larger time window to assess embryo health and to synchronize it with the mother for better implantation inside the uterus,' he added.

It will take further research to hone our ability to control this mechanism and safely induce diapause during IVF, but the researchers are optimistic that this work could lead to advancements in reproductive health treatments.