Race and Genetic Sensitivity to Hot and Cold Affect Labor Pain

A women's labor experience may be tied to her ethnicity as well as genetics, according to results from a clinical study presented at Anesthesiology 2010.

The study found differences in the receptor that controls uterine muscle contractions, the beta-2-adrenergic receptor (B2AR genotype C at the 27 position), which predicted later transition to active labor.

The genetic difference is common in Asian women and may account for findings that Asian women transition to active labor later. African American women had slower early stage labor, which could last over 36 hours. Heavy women also had much slower early labor. Epidurals were generally associated with a 30% longer labor time.

“We do not believe that the epidural actually slows the labor, but rather patients who are having a slower, difficult labor ask for an epidural earlier,” said Elena Reitman, MD, lead author of the study and post doctoral clinical fellow in Obstetrical Anesthesiology at Columbia University Medical Center.

The study identified the mother's sensitivity to cold was correlated with increased labor pain. Researchers hypothesized that the cold difference might be due to differences in a receptor on the uterine muscle that detected both cold and pain. The study's model predicted that women who require instrumental (such as forceps) vaginal delivery start off with more pain possibly because the baby's head is not in the most common presentation which is head-down, facing the mother's back, with its chin tucked to its chest and the back of the head ready to enter the pelvis.

The study prospectively enrolled 150 pregnant women from a single private practice who were near the time of giving birth. The researchers studied heat, cold and pressure threshold in the third trimester and all relevant labor and delivery information from electronic medical records, including: cervical dilation, pain scores, and labor management data (labor progression medication and pain medication treatment use). The researchers also performed DNA testing on the patients.

"We hope that the models that we created will allow women and their doctors to predict how fast or painful labor will occur so that they can make more informed choices about delivery," said Dr. Reitman.

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