Can Placental MRI Help Identify Elevated Risks for Adverse Pregnancy Outcomes?

In what may be the largest prospective study to examine the use of magnetic resonance imaging (MRI) to assess placental function, researchers found that quantitative MRI mapping may be beneficial in identifying increased pregnancy risks attributed to placental dysfunction.

In the new study, published by PLoS One, researchers utilized blood oxygen-level dependent MRI (BOLD-MRI) to assess quantitative placental T2*, a signal in the blood indicative of oxygen availability and blood flow in the placenta. Assessing placental T2* at three different times between 11 and 38 weeks of gestation, the study authors obtained a total of 797 MRIs for 316 pregnant women. Out of the study participants, 198 women had uncomplicated or normal pregnancies (UN), 70 patients had primary adverse (PA) pregnancy and 48 patients had secondary abnormal (SA) pregnancies.

In comparison to women with uncomplicated pregnancies, researchers noted significantly lower T2* values between the 15th and 33rd weeks of pregnancy in patients with primary adverse pregnancy. According to the study, these patients had preeclampsia with severe features, gestational hypertension or pregnancy outcomes that included a birth weight below the fifth percentile, stillbirth, or fetal death. The study authors noted an 0.71 area under the curve (AUC) for the link between placental T2* and PA pregnancy outcomes.

“Pregnancies complicated by PA had lower T2* across gestation and had a larger rate of decline in early and mid-gestation when compared to UN pregnancies,” wrote study co-author Matthias C. Schabel, Ph.D., who is affiliated with the Advanced Imaging Research Center at Oregon Health and Science University in Portland, Ore., and colleagues. “This difference is persistent across gestation and occurs prior to clinical diagnosis of adverse outcomes.”

The researchers noted that poor placental function may not persist through pregnancy and this diagnostic technique may allow for earlier modification of care for women deemed to have high-risk pregnancies. The MRI protocol in the study can also be easily implemented, according to the study authors.

“Placental MRI was performed using imaging protocols and pulse sequences that are available on virtually all modern MRI scanners, and analysis of these data requires only minimal post-processing to convert signal measurements to T2* values,” explained Schabel and colleagues.

The study authors also noted that the placental MRI protocol avoids the use of gadolinium-based contrast agents that are commonly utilized for MRI to assess tissue perfusion in non-pregnant patients.

There were no significant changes in placental T2* between those with uncomplicated pregnancies and patients with SA pregnancies with outcomes including fetal anomalies and spontaneous preterm birth, according to the study.

In regard to study limitations, the study authors acknowledge a small number of adverse outcomes and a relatively homogeneous study population that may prohibit extrapolation of the study findings to other populations. While MRI images were obtained with 3 Tesla scanning hardware in the study, they noted these devices lack the wider availability of 1.5 Tesla systems and are not considered the standard for obstetric imaging. Schabel and colleagues also pointed out that there is currently no standard definition of placental dysfunction.