In the management of twin pregnancies, the prevention of preterm birth remains a top priority in modern perinatal medicine. Since the risk of complications in multiple pregnancies is 10 times higher than in singleton pregnancies, scientists are constantly searching for diagnostic methods that enable early identification of danger.
A large-scale multicenter study was conducted in Poland, analyzing 2,004 cases of twin pregnancies. The results confirmed that measuring Cervical Length (CL) during transvaginal ultrasound scanning in the first trimester is an effective tool for predicting preterm birth before 34 weeks. Scientists combined data from routine check-ups at 11–13 weeks with various maternal biological and clinical indicators—age, Body Mass Index (BMI), history of previous preterm births, and PAPP-A hormone levels.
The study, which took place between 2015 and 2023 across five major fetal medicine centers, originally included 2,781 twin pregnancies. After excluding cases with fetal anomalies or incomplete data, 2,004 pregnancies remained in the final analysis: 1,590 dichorionic twins (two placentas) and 414 monochorionic twins (one placenta). The observation revealed that in 11.3% of cases (226 pregnancies), labor began spontaneously before 34 weeks.
The study highlighted a statistically significant difference between cervical length and the timing of delivery. In women who experienced preterm birth between 24 and 33+6 weeks, the average cervical length was 36 mm, whereas in the group with full-term deliveries, the average was significantly higher at 39 mm.
The data revealed a direct link between cervical shortening and the risk of complications: CL < 35 mm: The probability of preterm birth increases 3.42 times; CL < 30 mm: The risk increases critically, by 4.85 times.
However, cervical length is not the only factor. While diabetes and other clinical circumstances influence the course of pregnancy, multifactorial analysis highlighted that the most critical independent risk factor remains a history of previous preterm birth.
To ensure accuracy, experienced sonographers followed the strict protocol of ISUOG (International Society of Ultrasound in Obstetrics and Gynecology). The procedure required three essential conditions: an empty bladder, the use of a high-frequency probe, and clear visualization of the endocervical canal from the internal os to the external os. This standardized approach confirmed that 30 mm and 35 mm are the critical “cut-off” points that provide high predictive indicators for preterm birth in twins.
These findings significantly expand existing knowledge, as previously, a measurement of less than 25 mm in the secondtrimester was considered the primary warning sign. While first-trimester data was previously scarce, this study creates a solid evidence base for early screening. For instance, secondary analysis of the EVENTS study confirms that progesterone therapy is particularly effective specifically for twins where the cervical length is less than 30 mm.
Currently, this stands as the largest study conducted on the cervical status of twin pregnancies in the first trimester based on a unified, standardized protocol. Despite its significance, the scientific team points to certain limitations, such as its retrospective design and the limited two-week scanning window. Future prospective studies will further refine these standards and clarify clinical norms.
Source: BMC Pregnancy & Childbirth
