The study shows glands in the lining of the uterus store and deliver glycogen to the placenta during early embryo growth.
The study is the work of researchers from the University of Manchester in the UK, who describe their findings in the journal Placenta.
As the single-celled fertilized egg travels along the fallopian tube, it divides repeatedly so that by the time it reaches the womb or uterus it is an embryo - a mass of over 100 cells.
The newly arrived embryo burrows into the wall of the womb - it implants itself into the lining of the uterus.
There, it grows and develops into a fetus, in tandem with the placenta, through which it will eventually receive nutrients via the mother's blood supply.
But exactly how essential glucose and other nutrients reach the early embryo as it becomes a fetus - before it is large enough to link up to the mother's blood supply - has not been clearly understood before.
This stage of development is crucial, note the researchers, and other studies have shown that poor nourishment of embryos in these early weeks can affect children's health for the rest of their lives.
For example, research of children born to Dutch women who were in their first trimester at the end of World War II when there was a food shortage shows they were more likely to develop diabetes and heart problems, compared with those whose mothers enjoyed a good diet.
Glands in the lining of the uterus store and deliver glycogen to the placenta
In their paper, the researchers describe how they found gland cells in the lining of the uterus store glucose in the form of glycogen - a form of glucose that is readily mobilized, rather like starch in plants.
The glycogen is delivered to the placenta along with glycoproteins. These are used for energy and converted into the amino acids that help form the growing embryo.
Toward the end of the first trimester, the mother's blood supply to the placenta takes over the job of nourishing the fetus and the supply from the glands in the uterus tails off.
One of the authors, John Aplin, a professor of reproductive biomedicine at Manchester, says the discovery is a "leap forward" in our understanding of how the mother delivers nutrients to the child in the womb, because:
"A newly created embryo could not survive the full force of arterial blood from the mother. Although it has been known for some time that uterine secretions nurture the tiny embryo, the mechanism whereby the nutrients leave maternal cells and are delivered to the placenta has not been understood."
The study shows that it is not only good maternal nutrition in the early weeks that matters, but also what the mother eats before conception - as this is when the nutrients are stored in the gland cells.
Prof. Aplin says we are only just beginning to understand how nutrients reach the early embryo, so it is too early to give specific advice about what mothers-to-be should be eating based on this knowledge, beyond the general advice given to women. He concludes:
"However, as the study shows, the mechanism for nutrient delivery is quite different at this stage of development and making sure that a good supply of energy is in the gland cells is an important part of ensuring a healthy embryo."
Meanwhile, Medical News Today recently reported how eating fruits and vegetables with high pesticide residue may affect sperm quality. Compared with men who ate less than half a serving a day, those who ate more than one and a half servings a day of fruits and vegetables high in pesticide residue had lower sperm counts and lower percentage of normal sperm, researchers found.