Using Placental Proteins in Urine and Serum to Assess Gestational Age: A New Purpose for an Old Idea

Contraception; May 1, 2019; Vol. 99(5):319; doi:https://doi.org/10.1016/j.contraception.2020.02.007

Introduction: Clinicians commonly use ultrasound or pelvic exam to confirm that the duration of a pregnancy is below the accepted limit of 70 days before providing medical abortion. These methods are expensive and invasive, and they require an in-person visit to a facility with trained personnel and requisite equipment. A blood or urine test for estimation of gestational age (GA) would be highly beneficial, particularly in low resource settings or when providing abortion care remotely through telemedicine. In this exploratory study, we aimed to determine whether selected placental proteins could serve as the basis of such a test.

Method: We collected blood and urine samples from 245 healthy pregnant women presenting for abortion services or prenatal care across the gestational age spectrum, oversampling between 5-15 weeks. We assayed each serum specimen for seven different placental proteins and urine samples for two. We also tested urine specimens for hCG using commercially available point-of-care pregnancy tests with sensitivities from 25 to 10,000 mlU/ml. We examined the data to determine whether we could identify serum or urine concentrations that would reliably rule out late pregnancies.

Results: Serum concentrations of some proteins rose continuously over pregnancy. For two compounds, we noted a clear concentration threshold that distinguished pregnancies of >70days from earlier gestation. Similarly, we noted concentration thresholds for two other compounds that identified most pregnancies with GAs of >104 days. None of the urine pregnancy test differentiated women with GAs above or below 70 days.

Conclusions: Two compounds tested showed promise as serum markers to identify pregnancies ≤70 days gestation. If these results are validated by further research, these markers, alone or in combination with other markers, could be the basis of a test that could enhance access to abortion by screening out advanced gestation. Point of care urine hCG tests do not appear to be useful indicators of gestational age.