PRC Doctors Create Preterm Birth Blood Test

In an exciting development, scientists at the March of Dimes Prematurity Research Center (PRC) at Stanford have developed a promising blood test that may accurately identify women at risk of spontaneous preterm birth.

If further validated, the test, which detects elevation across three crucial pregnancy proteins, could be given in the first trimester, allowing doctors to red flag women at risk of preterm birth and intervene early, thereby reducing the chances of preterm delivery — one of the leading causes of infant death worldwide.

The test, recently detailed in the journal BMC Medicine, works by measuring levels of GPX3, NID1, and PAPPA2, three placenta-linked proteins Stanford researchers found to be both detectable in blood and elevated at early gestations in women who delivered preterm. Not only did the Stanford test outperform a clinically available preterm birth blood test, but it also identified preterm birth risk much earlier than the competition — as early as 5 weeks’ gestation. Though due to a small sample size at that gestation, further validation is necessary.

Study findings showed that the test predicted preterm birth with promising accuracy in a cohort of 25 women at the University of Alabama, as well as in three additional validation cohorts.

Senior study author and Stanford PRC investigator Dr. Bruce Xuefeng Ling called the research a “significant step forward.”

“The potential here is immense,” Dr. Ling said. “Early identification is a major breakthrough because preventative treatment, such as low dose aspirin and progesterone therapy, are most effective when started early — ideally before 16 to 18 weeks. By identifying high-risk pregnancies within this first trimester window, we could enable clinicians to move into a proactive care model, allowing more medical intervention before irreversible placental maladaptation occurs.”

Dr. Ling said the trio of biomarkers, which emerged as “golden nuggets” from 21 promising candidates, play important roles in pregnancy maintenance and can warn of a pregnancy that may be undergoing premature changes.

GPX3 is an antioxidant enzyme whose job is to defend the mother against inflammation and oxidative stress; this protein’s elevation indicates these processes, two of the key triggers of preterm birth, may be overactive. NID1, Dr. Ling said, is part of a biological “glue” that holds cells together at the maternal-fetal interface, or the area inside the uterus where maternal cells meet fetal cells. Elevation of this protein can signal an unraveling of the physical bond between mom and baby. Finally, PAPPA2, the scientist said, is a placental enzyme that elevates when problems arise in the placenta — or the placenta reacts to other pregnancy issues.

“In short, these proteins represent oxidative stress, tissue remodeling and placental invasion,” said Dr. Ling. “While our current paper focuses on using these as a predictive ‘early warning system’ in maternal blood, our next phase of research will involve deep genome and RNA sequencing. We want to map exactly which genetic ‘switches’ are flipping to cause these protein levels to rise so early in pregnancy.”

Dr. Ling is referring to the link between the three “golden nugget” proteins that make up the test, or panel, and their associated genes. That’s because getting to the panel required starting with a genomic screen after deciding on a hypothesis.

First, the team, which includes Stanford PRC principal investigator Dr. David Stevenson, theorized that women who end up delivering preterm are harboring biological signs of this outcome long before they go into labor. So, the team set sights on a biological sign, or biomarker, that could indicate the risk of preterm birth. They figured that proteins, some easily detectable in blood, could fit the bill. If some proteins behave differently in women who deliver preterm, measuring those proteins during pregnancy can identify women who may be headed for preterm birth long before they get there, giving doctors a chance to intervene.

Armed with their hypothesis, the team consulted a public database containing gene expression information linked to the placentas of women who delivered term and preterm. Once they found genes that were behaving differently in preterm placentas compared to term, they identified thousands of proteins that were associated with those misbehaving genes. Next, they identified which of those associated proteins were detectable in blood and came up with a short list of 21 candidates. From there, the team analyzed the Alabama blood samples for elevation in the 21 key proteins. And that’s when the three “golden nuggets” emerged as the strongest combined predictors of preterm birth.

“They were the only markers that showed a consistent, significant elevation in the blood of women who eventually delivered preterm,” Dr. Ling said.

He added that creation of the panel required “a rare convergence of multi-omics data mining, high-resolution mass spectrometry, and deep clinical expertise” made possible by “years of institutional memory at Stanford PRC headed by Dr. Stevenson in handling complex biological data to ensure that what we find in the lab will actually work for a patient in the clinic.”

To ensure the findings were reproducible and “not just a fluke of one population,” Dr. Ling said the team validated the panel in three independent cohorts — one from Stanford University and two from China — totaling 456 women and 1,048 blood samples. The validation found the panel to be predictive of preterm birth across all cohorts of diverse populations, and as early as 5 weeks’ gestation.

“Currently, the leading commercially available protein-based blood test for preterm birth risk offers its strongest predictive performance in mid-gestation, around 18 to 20 weeks, but with inconsistent performances across populations with different ethnic backgrounds,” Dr. Ling said. “In contrast, our Stanford three protein panel retains strong predictive accuracy much earlier and is robust across different ethnic groups.”

The team also showed the test is reproducible on the leading technology used in hospitals today, moving the panel “from ‘a promising laboratory finding’ to a ‘clinically robust predictor,’” Dr. Ling said.

Further validation of the test and a deeper dive into the cause of protein elevation in women heading toward early labor is already underway.

Dr. Ling and colleagues are simultaneously working on a three-pronged path: first, preparing to test the panel in larger, more diverse cohorts; second, working to ensure it can integrate seamlessly into clinic; and third, conducting deep genetic/phenotypic analysis to illuminate what placental mechanism is causing the proteins to rise in women at risk of preterm birth.

“By understanding the ‘why’ behind the markers,” Dr. Ling said, “we can come closer to our ultimate goal: enabling more effective, personalized prevention of preterm birth for families globally.”