301 - Predicting Comorbidities of Pregnancy: A Comparison Between Total and Free 25(OH)D and Their Associations with iPTH

Friday, April 28, 2023

5:15 PM – 7:15 PM ET

Poster Number: 301
Publication Number: 301.128

Caroline McWhorter, Medical University of South Carolina College of Medicine, Charleston, SC, United States; Molly Mead, Medical University of South Carolina College of Medicine, Johns Island, SC, United States; Megan D. Rodgers, Medical University of South Carolina College of Medicine, Charleston, SC, United States; Myla Ebeling, Medical University of South Carolina College of Medicine, Charleston, SC, United States; Judith Shary, Medical University of SC, Charleston, SC, United States; Danforth A.. Newton, Medical University of South Carolina, Charleston, SC, United States; John E. Baatz, Medical University of South Carolina College of Medicine, Charleston, SC, United States; Carol L.. Wagner, Medical University of South Carolina College of Medicine, Charleston, SC, United States

Presenting Author(s)

Caroline A. McWhorter, BS (she/her/hers)

Medical Student
Medical University of South Carolina College of Medicine
Charleston, South Carolina, United States

Background: Pregnancy is a unique time when amplified sex steroid concentrations promote an escalation in vitamin D binding protein (VDBP) synthesis, associated with increased total vitamin D (vitD) and metabolites. Free 25(OH)D increases disproportionately to total 25(OH)D, likely an adaptation to supply the woman and fetus with readily available 25(OH)D. Maternal total 25(OH)D and total 25(OH)D/iPTH are measures of vitD status and biomarkers for potential pregnancy complications. Free 25(OH)D and free 25(OH)D/iPTH may be better indicators of vitD status and predictors of pregnancy complications such as gestational diabetes (GDM), hypertensive disorders of pregnancy and preterm delivery.

Objective:

Determine if free 25(OH)D and its association with iPTH are more accurate predictors of comorbidities of pregnancy than total 25(OH)D and its association with iPTH.

Design/Methods:

In this post hoc analysis of the Kellogg Pregnancy Study, a double-blind randomized placebo-controlled trial, participants included 297 women with singleton pregnancies. 191 participants were randomized into a group receiving a daily prenatal (400 IU vitD₃) while 196 received a prenatal plus extra supplementation (4400 IU vitD₃). Blood and urine samples were collected monthly. 297 participants’ serum total 25(OH)D concentrations were measured using radioimmunoassay at baseline (visit 1) and 5-7 months’ gestation (visit 7). 93 had serum free 25(OH)D and iPTH concentrations measured using ELISA and immunoradiometric assay, respectively, at visit 1 and 7. 66 participants, who had both total and free 25(OH)D measurements were included in this post hoc analysis. A Student’s t-test analysis was performed.

Results:

There was a statistically significant relationship between free 25(OH)D/iPTH and the development of GDM at visit 1 (p=0.0003) and at visit 7 (p=0.001) (Figure 1). Total 25(OH)D/iPTH and GDM were significantly related only at visit 1 (p=0.029) (Figure 2). A lower mean free 25(OH)D/iPTH had a significantly stronger relationship with the development of GDM than total 25(OH)D/iPTH over gestational time. In this limited dataset, neither free 25(OH)D/iPTH nor total 25(OH)D/iPTH were significantly associated with increased incidence of preterm delivery, hypertensive disorders, or combined comorbidities of pregnancy.

Conclusion(s): Measuring free 25(OH)D as well as the functional vitD ratio of maternal free 25(OH)D/iPTH could serve as better indicators of comorbidities of pregnancy than total 25(OH)D or the ratio of total 25(OH)D/iPTH. More investigation is warranted on a larger sample size to improve validity and reproducibility.