Beta-2 adrenoceptor genotype and progress in term and late preterm active labor

Objective: We sought to evaluate whether beta-2 adrenoceptor (β₂AR) genotype at a functional polymorphic site encoding for amino acid residue 16 influences rate of cervical dilatation in term and late preterm active labor. Study Design: Subjects who underwent vaginal delivery at <34 weeks' gestational age from May 2006 through August 2007 were identified. Each subject had provided venous blood from which DNA was extracted for β₂AR genotyping. Digital cervical examinations with paired examination times were collected from intrapartum records. Rate of cervical dilatation in active labor was determined using linear regression. Rates were compared between genotype groups. Results: Among 401 subjects with satisfactory genotype and intrapartum data, overall rate of active labor was 0.76 ± 0.01 cm/h. When labor was compared by genotype, homozygous Arg/Arg16 subjects progressed at a slower rate (0.64 ± 0.03 cm/h) than all other pooled genotypes (0.8 ± 0.02 cm/h, P <.001). Conclusion: Homozygous β₂AR genotype encoding for Arg/Arg16 was associated with slower progress in active labor.