β2-adrenergic receptor genotype and other variables that contribute to labor pain and progress

β2-Adrenergic receptor (β2AR) activity influences labor. Its genotype affects the incidence of preterm delivery. We determined the effect of β2AR genotype on term labor progress and maternal pain.

We prospectively enrolled 150 nulliparous parturients in the third trimester and obtained sensory thresholds, demographic information, and DNA. Cervical dilation, pain scores, and labor management data were extracted with associated times. The association of genetic and demographic factors with labor was tested using mixed effects models.

Parturients who express Gln at the 27 position of the β2AR had slower labor (P < 0.03). They progressed from 1-10 cm dilation in approximately 21 h compared with 14 h among other patients. Asian ethnicity, previously associated with slower labor, is highly associated with this polymorphism (P < 0.0001). Heavier and black patients had slower latent labor (P < 0.01, 0.01). Neuraxial analgesia was associated with slower labor progress (P < 0.0001). It could take up to 36 h for parturients who were black and/or more than median weight (165 lb) to transition from 1 cm cervical dilation to active labor. However, after this active phase began, labor rates among these patients were similar to that of other parturients.

We detected a strong association between β2AR genotype and slower labor. Asian ethnicity may be a proxy for β2AR genotype. Black women and those of higher than average weight have slower latent labor. These results confirm many of the associations found when this mathematical model was applied to a large retrospective cohort, further validating this approach to description and analysis of labor progress.