The Battle of the Sexes isn’t just a movie. According to a new study, it’s an actual biological phenomenon that starts as early as the time we’re in our mothers’ wombs. During pregnancy, our parents’ genes go to war over the amount of nutrition we must receive, scientists have found.

Published in Developmental Celllast week, the study involved genetically-engineered mice to model human pregnancies. When a baby is in its mother’s womb, it receives nourishment from the placenta — an organ that “develops in [the] uterus during pregnancy” and “provides oxygen and nutrients to [the] growing baby [while] remove[ing] waste products from [the] baby’s blood.”

The focus of the present study, however, lies only in the former function: provision of nourishment. The purpose of the research is to understand how the fetus, the placenta, and the mother’s body communicate with one another so that scientists can figure ways to facilitate the healthy development of fetuses.

During pregnancy, it’s important that the fetus receives the right amount of nutrients for its development. “As it grows in the womb, the fetus needs food from its mum, and healthy blood vessels in the placenta are essential to help it get the correct amount of nutrients it needs… We’ve identified one way that the fetus uses to communicate with the placenta [through signals called “IGF2″] to prompt the correct expansion of these blood vessels,” Ionel Sandovici from the department of obstetrics and gynecology at the University of Cambridge, who is the first author of the study, explained.

“When this communication breaks down, the blood vessels don’t develop properly and the baby will struggle to get all the food it needs,” Sandovici added. This can result in infants dying at birth, or being at a greater risk of developing diabetes or heart diseases later in life.

This “communication stage,” however, is where the “battle” begins. Basically, it’s a “food fight” between the mother’s and father’s genes.

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Sandovici explained what, essentially, takes place is that “the father’s gene drives the fetus’ demands for larger blood vessels and more nutrients, while the mother’s gene in the placenta tries to control how much nourishment she provides… There’s a tug-of-war taking place, a battle of the sexes at the level of the genome.”

The relevance of this finding is that it has helped scientists understand one of the key reasons behind 10% and 15% of babies growing poorly in their mother’s womb. The study has led them to understand that excessive IGF2, resulting from a dominant paternal gene, can cause “too much growth”; inadequate IGF2, on the other hand, due to a dominant maternal gene, can result in “too little growth.”

“[P]aternally expressed genes are greedy and selfish… They want to extract the most resources as possible from the mother — but maternally expressed genes act as countermeasures to balance these demands,” Miguel Constância, Sandovici’s colleague from Cambridge University, who co-authored the study, said.

This tussle, however, isn’t automatically “a bad thing.” The researchers explained that the balance they strike is instrumental in the birth of a healthy infant.

Moreover, insights into the communication systems between the fetus, placenta, and mother, which this study delves into, could help scientists devise ways to enable the healthy development of the fetus and intervene if things go wrong. The researchers believe measuring levels of IGF2 in the fetus, for instance, and prescribing medications to alter them so that the fetus receives the right amount of nutritional intake, could be one way of going about things.

Whether it’ll work, however, only time and further research can tell.