Enter Your Email Address to Receive a
Copy of MedicExhange Member Demograhpics

New research shows, magnetic resonance spectroscopy (MRS) of amniotic fluid samples, coupled with statistical modeling, can determine gestational age in the late second and third trimesters.

"Specifically, for women who end up getting late prenatal care we may be able to use MRI / MRS to better estimate gestational age," senior author Dr. Aaron B. Caughey of the University of California, San Francisco, told Reuters Health by e-mail.

"More broadly," he said, " MRI /MRS may have many uses for pregnant women particularly in fetal diagnosis and evaluation because it can evaluate the fetus in functional ways that ultrasound cannot."

Predictions of gestational age that are based on ultrasonography in the third trimester can be off by three weeks or more in either direction, Dr. Caughey and his colleagues say in a May 3rd online paper in the American Journal of Obstetrics & Gynecology.

In contrast, their new formula predicts gestational age to within two weeks - but what's needed now is for their model to be validated in larger populations.

To evaluate their approach, the team used MRS to determine concentrations of 21 amniotic fluid metabolites in 95 samples from women who underwent clinical examination of fetal lung maturity or karyotyping.

The researchers obtained the amniotic fluid samples when the fetuses were a mean gestational age of 31.7 weeks. This estimate was based on ultrasound in the first trimester or the date of the last menstrual period.

They entered metabolite concentrations, inverses, natural logs, and squares as predictive variables in a stepwise linear regression model, and developed the following formula:

Gestational age = 64.922 - (14.456 x alanine) + (4.965 x natural log of creatinine) - (0.931 x glucose) - (5.202 x valine)

With this formula, for all samples, the average error was plus or minus 1.75 weeks. For the second trimester, it was plus or minus 2.21 weeks and for the third, it was plus or minus 1.59 weeks.

The results suggest that gestational age "can be predicted accurately with concentrations of only alanine, the natural log of creatinine, glucose, and valine quantified by MRS," the researchers say. "The simplicity of the model and the strong correlation between metabolic profiles and fetal developmental states suggest a role for this spectroscopic dating technique in the clinical setting in late pregnancy," they add.

Source: Reuters Health