The safety in this setting is based on the presumption that the angle between the cervix and the vaginal probe is sufficient to prevent the probe from inadvertently slipping into the cervix and that real-time imaging is used throughout the procedure to assess the relationship between the probe tip and the cervix [33]. US Cervix Transperineal Transperineal US is an alternate approach to transvaginal evaluation of the gravid cervix and may be useful in certain clinical scenarios, such as large body habitus or when incomplete distention of the bladder limits the transabdominal cervical assessment. The transperineal approach is superior to transabdominal US, and transperineal assessment of the gravid cervix has been shown to be comparable to TVUS [27]. Good correlation between CL measurements obtained transperineally and transvaginally have been reported in normal gravid patients at each trimester [26-28]. In a study by Hertzberg et al [28], similar levels of diagnostic confidence were achieved with both transperineal and transvaginal approaches, noting a clear preference expressed for the latter. CL was found to be comparable after 20 weeks gestational age; however, CL measured between 14 and 20 weeks gestational age was statistically shorter via the transperineal approach. Given the apparent difference in accuracy of transperineal CL in the early second trimester, the authors suggested performing transvaginal imaging when short CL are obtained transperineally in the early second trimester. In a study of women between 22 and 24 weeks gestational age, Cicero et al [26] reported satisfactory transperineal visualization of the cervix in approximately 80% of cases. CLs obtained by the transperineal approach during this gestational age were also comparable to those obtained transvaginally. TVUS is the preferred approach for assessment of the gravid cervix in high-risk patients, but there may be instances in which TVUS is not possible because of patient discomfort or preference.
Assessment of Gravid Cervix. The safety in this setting is based on the presumption that the angle between the cervix and the vaginal probe is sufficient to prevent the probe from inadvertently slipping into the cervix and that real-time imaging is used throughout the procedure to assess the relationship between the probe tip and the cervix [33]. US Cervix Transperineal Transperineal US is an alternate approach to transvaginal evaluation of the gravid cervix and may be useful in certain clinical scenarios, such as large body habitus or when incomplete distention of the bladder limits the transabdominal cervical assessment. The transperineal approach is superior to transabdominal US, and transperineal assessment of the gravid cervix has been shown to be comparable to TVUS [27]. Good correlation between CL measurements obtained transperineally and transvaginally have been reported in normal gravid patients at each trimester [26-28]. In a study by Hertzberg et al [28], similar levels of diagnostic confidence were achieved with both transperineal and transvaginal approaches, noting a clear preference expressed for the latter. CL was found to be comparable after 20 weeks gestational age; however, CL measured between 14 and 20 weeks gestational age was statistically shorter via the transperineal approach. Given the apparent difference in accuracy of transperineal CL in the early second trimester, the authors suggested performing transvaginal imaging when short CL are obtained transperineally in the early second trimester. In a study of women between 22 and 24 weeks gestational age, Cicero et al [26] reported satisfactory transperineal visualization of the cervix in approximately 80% of cases. CLs obtained by the transperineal approach during this gestational age were also comparable to those obtained transvaginally. TVUS is the preferred approach for assessment of the gravid cervix in high-risk patients, but there may be instances in which TVUS is not possible because of patient discomfort or preference.