Serotonin is widely known as one of the human body’s “happiness hormones.”
But Dr. Harvey Kliman, director of the Reproductive and Placental Research Unit at Yale, said serotonin is also a growth hormone — and it works in ways that can result in bigger or smaller babies in utero.
Serotonin “causes the placenta to grow up until 20 weeks, and then in the second and third trimester, most of the serotonin ends up going into the fetus to cause the fetus to grow,” he said.
A physician scientist who has studied the placenta for 40 years, Kliman published a study Sept. 3 showing it’s the placenta that regulates how much serotonin gets into the fetus, and too much of it results in a larger fetus.
“Serotonin equals cell proliferation, more cells, more growth,” he explained.
“And it's known that children with autism have larger brains and heads, and their brains are more folded,” he said. “So we said in this paper, it's very hard to prove this, but we hypothesized that the increased serotonin going through the placenta of somebody that is going to have a child with autism, is that their placenta had more transport of serotonin.”
‘This is not something caused by vaccines’
The research, published in the journal “Endocrinology,” is another study adding to the list of scientific papers debunking the messaging that autism is caused by vaccines.
“This is not something caused by vaccines, this is pre-ordained and preset in utero and being, I think, controlled by the amount of serotonin that’s been delivered through the placenta of this particular child, and then ultimately into their body and brain,” Kliman said.
He emphasized that more research is needed to determine what can be done with these findings from a pharmacological standpoint to help reduce the rates of autism in utero.
There is no clinical data currently to support medical intervention, but Kliman said in the future, parents at a higher risk of giving birth to a child with autism could get a prescription for a class of antidepressants known as selective serotonin reuptake inhibitors (SSRIs) during pregnancy.
If a parent has a child with autism, it puts them at a higher risk of giving birth to another child with autism. And so an SSRI might be able to “dampen down the amount of serotonin that is being delivered through the placenta to the next child.”
Decades of research
Some 20 years ago, Kliman said a group of lawyers contacted him about what the placentas of parents giving birth to children with autism looked like. The lawyers wanted to know if autism could have origins in utero, and not after vaccinations in early childhood. That got Kliman started down the path of serotonin’s role in autism, and the placenta’s role in delivering it to the fetus.
But serotonin is somewhat of a Goldilocks, he said, pointing to illustrations and charts presented to Connecticut Public’s health reporter over Zoom. At age 72 with a Ph.D in addition to a medical degree, Kliman has spent decades educating students and patients.
When the fetus gets too little serotonin, the babies are smaller, but there was no indication that they failed to thrive, he said.
“What we don't want is a patient who's pregnant to be so depressed that they potentially end their life because they're depressed,” he said. “And if there's a way to prevent that, by taking antidepressants, SSRIs in particular, that is a gift to them.”
Role of SSRI use during pregnancy
Kliman’s findings come on the heels of a Food and Drug Administration expert panel meeting in July that raised concerns about SSRI use in pregnant people, and stated that doctors do not adequately counsel patients on the risks.
In response, Dr. Steven J. Fleischman, president of the American College of Obstetricians and Gynecologists, said in a statement “robust evidence has shown that SSRIs are safe in pregnancy and that most do not increase the risk of birth defects. However, untreated depression in pregnancy can put our patients at risk for substance use, preterm birth, preeclampsia, limited engagement in medical care and self-care, low birth weight, impaired attachment with their infant, and even suicide.”
Data shows SSRIs are not without risks to the fetus, like many other medications during pregnancy.
“The risks listed include primary pulmonary hypertension — I have never seen this — preeclampsia and neonatal adaptation syndrome,” said Dr. Kate Pascucci, an OB-GYN in West Hartford. “We choose SSRIs because they are the better studied group of medications in pregnancy.”
Pascucci said she took SSRIs during her three pregnancies.
“But for some women, another drug may be more appropriate and each patient's risk needs to be assessed individually. The most important thing for a healthy fetus is a healthy mother,” she said. “Suicide is a leading cause of preventable maternal mortality in the United States.”
