TUESDAY, Oct. 11 (HealthDay News) -- Preeclampsia, a potentially
dangerous spike in blood pressure during pregnancy, may be due to a
microscopic battle going on within the placenta between cells
directed by the father's genes and those directed by the mother, a
new study suggests.
Though not the first research to link preeclampsia with the
activity of cells in the placenta, the new report adds more details
about the underlying mechanism that may be causing the problem.
During prenatal growth, certain genes are expressed or
repressed, depending on their parental origin. In the placenta, the
father's gene expression dominates.
In a normal pregnancy, trophoblasts, a father-directed cell,
invade and attack the blood vessels that bring blood from the
mother into the placenta. The trophoblasts attach to the walls of
blood vessels, increasing the flow of blood and enabling the baby
to grow and receive the nutrients it needs to thrive, explained
study author Dr. Harvey Kliman, a research scientist in the
department of obstetrics, gynecology and reproductive sciences at
Yale University School of Medicine.
But at the same time, the mother's immune system cells
(lymphocytes) rush to kill the invasive trophoblasts. If the
lymphocytes succeed in killing the trophoblasts, then there isn't
enough blood flow to the placenta -- causing blood pressure to
"The placenta is responsible for keeping the fetus alive. It will do whatever is necessary to do that," Kliman said. "The placenta has a sensor, a molecular mechanism that senses how much blood is flowing into the placenta. If there's not enough blood, you will become hypertensive."
Though his research didn't investigate that mechanism
specifically, it's well known that an obstruction to blood flow to
another organ, the kidney, leads quickly to primary renal
hypertension, a type of high blood pressure. The placenta, he says,
has a similar internal thermostat. If it's not getting enough
blood, blood pressure goes up in an attempt to get more blood into
the organ and prevent the fetus from dying.
So, to outwit the mother's lymphocytes, the father's
trophoblasts create a diversion. Trophoblasts make a protein
(PP13), which exits the blood vessels and travels into the lining
of the uterus.
The lymphocytes rush to deal with that inflammation, ignoring
"All of the mother's soldiers are being diverted and focusing on the PP13 instead of going after the trophoblasts," Kliman said. "It's very sneaky."
The findings are published in the Oct. 11 online issue of
In the study, researchers used placental tissue from women in
the United States and Israel.
Prior research had found that when levels of the PP13 protein
are low early in pregnancy, women were more likely to develop
preeclampsia several months later, but why PP13 contributed to that
Kliman said the molecular battle is driven by the
father-directed trophoblasts, which are trying to create conditions
for a big, healthy baby, while mother needs to tamp down on growth
so that the fetus is small enough to get through the birth
"The mother does not want to die. The father wants a big baby. So they compromise," he said. "If the invasive trophoblasts are killed, the blood vessels wouldn't open up, and the baby would die. If the father wins the battle and the trophoblasts are able to go into the uterus, the baby would grow too big and the woman would die."
Dr. Jill Rabin, chief of ambulatory care in the obstetrics and
gynecology department and head of urogynecology at Long Island
Jewish Medical Center in New Hyde Park, N.Y., said the research
adds "teeth" to the theory of the role of trophoblasts in
"It makes a lot of sense that the mother's immune system had to be tricked somehow, otherwise how would this happen that a placenta or a fetus could set up housekeeping inside the mother?" Rabin said. "The placenta is very smart."
Eventually, the hope is that understanding the underlying
biological mechanism that causes preeclampsia will lead to
treatments, Rabin said, adding that more studies are needed to
confirm the findings.
Preeclampsia usually shows up in the latter half of pregnancy.
Many cases are mild, but it can progress to eclampsia, or severely
elevated blood pressure and protein in the urine that can lead to
seizures and puts a woman at risk of stroke or organ damage. The
only cure for it is to deliver the baby, experts said.
American Academy of Family Physicians has more on