The following is a summary of “Real-time ultrasound demonstration of uterine isthmus contractions during pregnancy,” published in the January 2024 issue of Obstetrics and Gynecology by Farràs, et al.
For a prospective observational study, researchers sought to investigate the prevalence and characteristics of isthmic contractions after bladder voiding in the second trimester of pregnancy, assess their impact on cervical length assessment, and propose a new method for objectively evaluating the presence and intensity of isthmic contractions.
Long videos of the uterine cervix were recorded in 30 singleton pregnancies during the second trimester after bladder voiding. Changes in isthmic length and cervicoisthmic length over time were assessed. A novel approach was used to measure isthmic length, calculating the distance from the base of the cervix to the internal os, including the isthmus.
Isthmic contractions were observed in 43% of pregnant women (95% CI, 26%–62%) after bladder voiding, with a median time for complete isthmus relaxation of 19.7 minutes (95% CI, 15.0 to not available). No significant differences in maternal characteristics were found between individuals with and without contractions. The proposed method for measuring isthmic length provided an objective assessment of the presence and intensity of isthmic contractions. A cutoff of 18 mm in isthmic length effectively differentiated pregnant women experiencing contractions. Additionally, a characteristic undulatory pattern was identified in half of the cases with contractions.
Isthmic contractions are common after bladder voiding in the second trimester of pregnancy and can impact cervical length assessment. It was recommended that a cervical assessment be performed at least 20 minutes after bladder voiding to minimize measurement bias and avoid misdiagnosing placenta previa. The novel method for measuring isthmic length offers an objective means of evaluating isthmic contractions. Further research was needed to understand their physiological role in pregnancy and childbirth.