Our research found that most obstetricians follow the policies of the Ministry of Public Health in that they perform screening even if they have not received formal certification in the conduct of the procedure. However, the main problem they face are huge workloads; therefore, most tertiary hospitals only carry out the examinations for high-risk pregnant women.
The current effective preventative measure for preterm deliveries is the use of progesterone. (17) Much research supports the position that obtaining cervical length measurements is an effective way of screening for pregnant women with a short cervix; the procedure has proven to be highly cost-effective and presents limited risk. (18, 19) As only a small proportion of women who have a preterm birth have risk factors, and a substantial number of preterm deliveries occur in nulliparous women, universal transvaginal cervical length screening is recommended to identify women at risk of a preterm birth. (20) The American College of Obstetricians and Gynecologists and the Society of Maternal and Fetal Medicine have published clinical guidelines for universal transvaginal cervical length screening, and for the administration of either vaginal progesterone or a cervical cerclage to treat pregnant women with a short cervix. (18, 19)
Nevertheless, there remains some controversy about the performance of cervical length measurements for low-risk women. There are also questions about the standards to be used for, and the repeatability of, measurements. Even though clinical trials have demonstrated that the use of the screening method and progesterone therapy significantly reduces the risk of preterm deliveries and is worthwhile, the invasive nature of the procedure raises concerns for some patients. While the benefits of conducting additional cervical length screening through a universal program and providing what may prove to be unnecessary progesterone treatment still need to be substantiated, cervical length measurement is currently used very extensively. (21) One of the key barriers to the full implementation of universal screening in Thailand is the excessive volume of routine, urgent, and necessary tasks of physicians and nurses. Other major barriers are (1) some physicians do not believe that the provision of universal screening can justify the requisite labor and funding; and (2) there is inadequate funding by government agencies for both screening and the provision of cost-free progesterone. Therefore, careful reconsideration of the need to perform universal screening is warranted.
Work by Temming et al. (22) found that cervical length measurements tended to be rejected by women with one or more of the following characteristics: African, American, or Hispanic; obese; multiparous; younger than age 35; and a smoker. Their research also revealed that the rate of early spontaneous preterm births was higher among those women than other groups. In addition, the researchers established that the incidence of pregnant women with a cervical length of ≤ 20 millimeters was 1.1%, with no significant differences in the preterm delivery rates of women who underwent, and those who did not undergo, the measurements. (22)
Pregnant women with a full-term delivery have a low incidence of short cervices. (23) Miller et al. reported that the incidence of a cervical length ≤ 25 millimeters was only 0.9% among 18,250 women who underwent transvaginal screening. (24) Similarly, in several institutional studies, Facco and colleagues found that a short cervix was less common among women with a low risk of preterm delivery. (25) Therefore, it appears reasonable to restrict transvaginal cervical-length measurements to pregnant women with a high risk of a short cervix or a preterm delivery (24) in order to decrease the workloads of physicians and nurses.
Adequate human resources and ultrasound machines for cervical screening are on hand at nearly all tertiary hospitals in Thailand. On the other hand, no government funding is presently made available to women to cover the costs of their examinations nor the provision of progesterone. Reserving transvaginal cervical screening for high-risk groups would release funds that could then be used to support the introduction of cost-free progesterone. A cost-effectiveness analysis of providing transvaginal screening only to such groups would need to be conducted.
Cervical length measurements can be safely performed during the period of fetal structural examination, at 20–24 weeks of gestation. A transabdominal cervical length measurement should be offered to pregnant women who have serious reservations about undergoing a transvaginal measurement. (23, 24) Unfortunately, transabdominal measurements can be used only with some pregnant women. (26) When the procedure is performed, the cervical length will be longer than that determined by a transvaginal measurement because the pregnant women must have a full bladder in order for the ultrasound operator to obtain a clear vision. (26) Therefore, the cervical measurement should be routinely performed using the transvaginal route because it is currently the most effective method. Transabdominal measurements should be reserved for women who are clearly reluctant to undergo a transvaginal assessment.
As to the cost-effectiveness of screening programs, a transabdominal ultrasound should be performed for low-risk women with a fetal anatomy survey at 19–20 weeks gestation, while the more accurate but relatively costly transvaginal ultrasound may be worthwhile reserving for high-risk populations. (27) The benefits of this approach are, firstly, the additional costs associated with transvaginal screening can be avoided (28) and, secondly, the use of the dual methodologies improves the possibility that screening can be affordably performed for all pregnant women.
Vaginal progesterone administration to women with a cervical length of ≤ 25 millimeters has been shown to significantly reduce the risk of preterm births. (29) Providing funding to make the supply of progesterone free of charge should be considered as a national policy to prevent preterm births. However, one of many barriers to universal screening is the limited knowledge of the physicians involved in counseling pregnant women. If physicians do not believe in the prevention strategies, the need for universal screening, and the benefits of progesterone treatment, the utilization of screening will be impaired. (30, 31)
A physician’s expertise in performing a measurement will greatly affect the results of the examination. Wrong results may lead to unnecessary treatment or missed opportunities to prevent preterm births through the administration of vaginal progesterone. The performance quality and the learning curve associated with obtaining accurate measurements are of critical importance. (32, 33)
In summary, in recognition of the heavy workloads of physicians, transvaginal cervical--length measurements should be reserved for pregnant women at high-risk of a preterm delivery. A public health education campaign should also be conducted to promote the advantages of universal transabdominal cervical-length measurements at 20–24 weeks of gestation for low-risk cases. The incidence of short cervices is not high in the low-risk population, and fewer hospital costs are incurred with the transabdominal procedure than a transvaginal ultrasound. Physicians should be trained in the execution of both procedures. In addition, pregnant women must be fully advised about the benefits and risks of cervical length screening to help them in their decision-making regarding the selection of treatment. Moreover, the availability and prompt usage of vaginal progesterone needs to be reviewed. To achieve successful implementation of universal screening, the incidence and significant complications associated with preterm births should be communicated to all pregnant women. Continuous monitoring of preterm birth rates is essential in areas where universal screening is implemented to ensure that positive results are achieved.