OXYTOCIN RECEPTION EXPRESSION IN PREGNANCY: “IS IT TIME TO ADD THE PIT?”

Objectives

We aimed to measure oxytocin receptor (OXTR) expression changes in the myometrium throughout pregnancy to inform clinical management of post-abortion hemorrhage.

Methods

We obtained myometrial tissue through transcervical core needle biopsies under ultrasound guidance in anesthetized participants immediately following procedural abortion. We also obtained tissue from non-pregnant and term control participants. We compared relative OXTR expression throughout pregnancy using quantitative PCR (qPCR) to evaluate gene expression and immunohistochemistry to assess OXTR protein in samples.

Results

We collected myometrial samples from 29 participants including n=22 following abortion at 6-26 weeks, n=3 undergoing cesarean delivery at term prior to labor, and n=4 undergoing laparoscopic permanent contraception (non-pregnant). Using qPCR, we observed an increase in relative OXTR expression with increasing gestational age. Compared to non-pregnant levels, the relative expression ranges increased from 2.5-fold (SD 3.9) in the first trimester to 96-fold (SD 10.3) at term. To further investigate the changes in expression in the second trimester, we compared mRNA expression in early-, mid-, and late-second trimester subgroups. Compared to the first trimester (<14 week), relative expression increased by 5.8-fold at 14-17 weeks, 16.2-fold at 18-20 weeks, 22.4-fold at 20-26 weeks, and 38.4-fold at term (>37 weeks). Immunohistochemical staining confirmed gestational week dependent increases in OXTR protein levels in the cytosol of myometrial cells.

Conclusions

This study defines changes in OXTR expression throughout pregnancy and provides evidence for an increase in the second trimester. This supports the use of oxytocin in second trimester hemorrhage management, with a notable increase in expression by 18 weeks.