While studying pre-eclampsia, a disease that affects pregnant women, researchers at the University of Missouri happened upon a new type of human embryonic stem cell.

They say the previously unknown type of transitional stem cell will help advance research on pre-eclampsia and other little-understood reproductive disorders.

"These new cells, which we are calling bone morphogenetic protein (BMP) -primed stem cells, are much more robust and easily manipulated than standard embryonic stem cells," lead researcher R. Michael Roberts, a professor of biochemistry at Missouri, said in a press release. "BMP-primed cells represent a transitional stage of development between embryonic stem cells and their ultimate developmental fate, whether that is placenta cells, or skin cells or brain cells."

Roberts and his colleagues discovered the new stem cells while attempting to grow placenta cells in order to better understand the causes of pre-eclampsia -- a disease that causes mother and child to experience dangerously high blood pressure and urine overloaded with protein. The disease can lead to a number of complications and if not treated properly can require an emergency Caesarean sections early in pregnancy.

While trying to coax embryonic stem cells into the pluripotent state, whereby they are more easily transformed into different types, researchers discovered a transitional state.

"Previously, the common thought was that embryonic stem cells transitioned straight from stem cells to their end products," Roberts said. "These new stem cells made us realize that embryonic stem cells exist in a number of different transitional states, which likely resemble those encountered in the early stages of embryos."

The researchers found the newly identified BMP-primed cells to be easier to work with in the lab setting, as they were easier to grow and more uniform in behavior -- each cell responding to manipulation in similar ways.

"This should open the door for future stem cell research that is much more efficient," Roberts added. "We now have new stem cells that are easier to manipulate since they are already at the key transitional precipice before changing into placenta cells, skin cells or any other kind of cell that makes up the human body."

The research was published in the science journal PNAS.