Jim Kling

October 25, 2010

October 25, 2010 (San Diego, California) — Black and Asian mothers are more likely to experience protracted transitions to active labor, whereas heavier mothers experience slower latent labor and faster active labor, according to research presented here at the American Society of Anesthesiologists 2010 Annual Meeting.

Patient characteristics can be predictive of the progress and pain of labor, but demographic attributes contribute only a small portion to the variation seen. There is evidence that variations in 2 common single-nucleotide polymorphisms (SNPs) in the B2AR gene affect the likelihood of preterm labor, and a SNP in the opioid receptor has been linked to pain sensitivity and the need for opioids after surgery, reported lead investigator Elena Reitman, MD, an obstetric and seizure fellow at Columbia University in New York City.

To evaluate the effects of these genetic variables, the researchers conducted a prospective study of 150 women in labor to deliver their first child from a single private practice. They measured heat, cold, and pressure thresholds in the third trimester, and obtained labor and delivery information from electronic medical records. They used polymerase chain reaction to amplify genes for sequencing, a biexponential function to model labor progress, and a sigmoidal function to model labor pain. The team used NONMEM software to test covariates.

The researchers found that B2AR genotype CC at position 27 was associated with delayed transition to active labor (P < .04). Heavier maternal weight was associated with faster active labor but slower latent labor (P < .04). Slower latent labor occurred among black mothers, and a later transition to active labor occurred in Asian mothers (P < .0004). Epidural administration was associated with 73% slower progress (P < .0001).

The homozygous mutant (GG) at position 118 of the OPRM1 gene occurred in 12% of the participants, all of whom were Asian or white. Upon further analysis, the researchers found that women with the OPRM1 (GG) genotype developed pain more quickly (P < .01). Other analyses revealed that taller patients had slower development of pain (P < .04), and that instrumental vaginal delivery was associated with more pain in early labor (P < .01).

Optimization for ethnicity revealed that black patients developed pain faster (P < .02), and that taller patients developed pain more slowly (P < .04). Instrumental vaginal delivery and increased sensitivity to a cold stimulus was associated with more pain in early labor (P < .01 and P < .02, respectively).

"Women who have this (CC) genotype in B2AR transition much later to active labor. Interestingly, most of our Asian patients have that genotype. When we broke down the analysis, we saw that the Asian women also have later transitions to active labor," Dr. Reitman told Medscape Medical News. "Our models also show that larger, heavier patients have much more prolonged latencies of labor," she added.

Patients that eventually required instrumental delivery began with higher pain scores at the very beginning of labor.

Dr. Reitman's team is designing a Web-based labor progress calculator that will allow the input of different patient parameters to predict the time to full dilation and ongoing labor.

"Their findings that they could use some predictors to make an assessment of the overall progress of labor is likely to be very exciting, Judy Kersten, MD, a professor of anesthesiology at the Medical College of Wisconsin in Milwaukee, who moderated the session, told Medscape Medical News.

"If we can identify patients who might be at greater risk for a prolonged labor, we might be able to institute some type of therapeutic approach to address that and prevent operative deliveries. They didn't talk about what the ultimate effect was in terms of the likelihood of someone sustaining an operative delivery. That's one of the important questions one would want to address," Dr. Kersten noted.

The study did not receive commercial support. Dr. Reitman and Dr. Kersten have disclosed no relevant financial relationships.

American Society of Anesthesiologists (ASA) 2010 Annual Meeting: Abstract 787. Presented October 18, 2010.

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