This previously unknown connection - discovered by scientists at the University of Aberdeen and Witten/Herdenke University in Germany - has paved the way for a new technique to detect development problems during pregnancy.
The findings show that synchronisation between the heartbeats of a mother and foetus only occurs when the mother breathes rhythmically. If this synchronisation does not occur, it signals that something may be wrong with the development of the foetus.
This opens up the potential for early medical intervention to be taken whilst the child is still in the womb.
Dr Marco Thiel - one of a team of physicists from the University of Aberdeen who worked on the study said: "Pregnant mothers often report an awareness of a bond with their child, but until now there has been no hard evidence to suggest this bond is reflected in the interaction of their heartbeats. Our findings reveal that synchronisation between the heartbeat of a mother and foetus does actually occur - but only when the mother is breathing in a rhythmical fashion. The foetus can sense the rhythmical shift in the mother's heartbeat and adapts its own heartbeat accordingly."