August 25, 2022 | The placenta—a transient organ that develops during pregnancy—supplies oxygen, replenishes nutrients, and removes waste from the fetal environment. In a dysfunctional state, the organ causes severe issues in fetal development, preterm labor, lifelong health issues, and morbidity.
Scientists have long recognized that early detection of placental dysfunction increases the chances of a healthy pregnancy. However, no reliable diagnostic tool anticipates these complications throughout gestation.
Currently, obstetric imaging is primarily conducted via ultrasound. While still a valuable tool for identifying existing issues, it is not a predictive or preemptive device. Specialized methods such as uterine artery Doppler velocimetry—a technique determining maternal blood flow quality as a predictor of placental attachment—can predict preeclampsia and fetal growth restriction but not in cases associated with late-onset morbidity.
Fulfilling a need in obstetric care, Oregon Health & Science University (OHSU) researchers created a new magnetic resonance imaging (MRI) technique to quantify placental blood oxygen levels and predict pregnancy complications across gestation. Since 2015, the team has received two major funding awards from the National Institutes of Health’s Human Placenta Project for their research.
“Any research that helps us find ways to improve prenatal care is crucial,” said Victoria H. J. Roberts, Ph.D., study co-lead and OHSU’s Oregon National Primate Research Center Division of Developmental and Reproductive Sciences research associate professor, in a press release. “Pregnancy can be extremely taxing, both emotionally and physically, especially for someone who is experiencing a complicated pregnancy. It’s exciting that this research has identified a more effective way to detect complications early in pregnancy, so clinicians are able to provide the best care to the mother and developing baby.”
Predictive Diagnostic Imaging
Published in PLoS One (DOI: 10.1371/journal.pone.0270360), Roberts and co-lead Antonio Frias, M.D., OHSU School of Medicine Obstetrics and Gynecology professor, monitored 316 women between 11 and 38 weeks gestation with low- and high-risk for pregnancy complications. The dual-site longitudinal study examined each patient no more than three times, totaling 797 imaging studies between OHSU and the University of Utah Health Services Center.
Each patient fell into one of three categories: uncomplicated (UN), primary adverse (PA), or secondary abnormal (SA) pregnancy. PA pregnancies included hypertension-related complications such as preeclampsia as well as low birth weights and stillbirths. The SA group comprised high-risk patients that did not fit the PA category, such as those that experienced spontaneous preterm births and fetal anomalies.
The team used placental MRIs to extract T2* measurements as part of the imaging study. T2 stands for transverse relaxation time, which marks how long it takes excited protons to reach equilibrium during an MRI. T2*, or T2-star, is considered the “observed” T2 measurement and accounts for inhomogeneities in the magnetic field.
T2* values, which naturally follow a reverse sigmoid curve during pregnancy, are sensitive to blood oxygen saturation. Therefore, as the values change in response to maternal placental blood flow and fetal oxygen uptake, they provide valuable and predictive information regarding potential adverse outcomes.
Using UN values as a baseline, the team found that median placental T2* measurements were markedly lower in the PA group, with a larger rate of decline starting at 15 weeks gestation and continuing through 33 weeks. The difference was persistent throughout pregnancy and could be detected before patients received an adverse clinical diagnosis.
There was no statistical difference between the UN and SA patient groups. This finding may be related to genetics and its role in developing adverse outcomes independent of placental function. However, the team acknowledges that the defining SA characteristics were imperfect and that slight adjustments to the classification process are worth further investigation.
Nevertheless, the study suggests that T2* values can accurately identify a primary adverse pregnancy as early as 10 to 20 weeks, with the most substantial predictive power between 20-30 weeks.
Except for a few site-related differences, such as high altitude-induced low oxygen saturation in Salt Lake City patients, the study produced similar results at both sites, demonstrating reproducibility. Additionally, the required sequences are widely available on almost all modern MRI scanners; therefore, no other equipment or upfront costs are needed. The method can also be conducted without gadolinium-based contrast agents, which pregnant patients should avoid.
Thanks to the researchers at OHSU, healthcare professionals have an improved non-invasive diagnostic tool that could change the course of preventive obstetrics. The team hopes to see improved clinical care nationwide, with T2* values as the foundation for biomarker discoveries.