General information
Our research indicated that 647 papers have been published across 136 academic journals, involving 3214 authors and 1010 institutions from 65 countries/regions. We observed a consistent upward trend in publications related to the prediction of sPTB from 2004 to 2023. This growing number of articles revealed that the level of teamwork and funds in the field is constantly improving and many achievements have been made. This study will be helpful in guiding researchers in selecting relevant topics and in finding suitable teams to collaborate with and research platforms to use. The United States, as the world leader in both economics and science, has contributed the highest number of articles on the prediction of sPTB (n = 245, 39.26%). While, about 80% of top institutions were from the United States. Close collaborations were observed between countries/regions and institutions, but the cooperation among agencies is closer than between countries, suggesting international collaborations need to be further developed.
The top 10 academic journals published 343 articles, accounting for 53.01% of all articles. The American Journal of Obstetrics and Gynecology (n = 74) leaded in the number of publications among all journals, followed by the Journal of Journal of Maternal Fetal Neonatal Medicine (n = 71) and Ultrasound in Obstetrics Gynecology (n = 49), suggesting a significant interest in sPTB prediction research in these journals. These data are valuable for future scholars in choosing journals when submitting manuscripts related to the prediction of sPTB. By analyzing authors and co-cited authors, we identified Berghella V (n = 27 and 206 co-citations) and Iams JD (n = 24 and 283 co-citations) as the most productive and influential researchers. BerghellaV is an outstanding expert in obstetrics and gynecology, and has developed the maternal-fetal evidence-based guidelines. In addition, BerghellaV is committed to the application of CL in predicting sPTB. [15]. At the same time, exploring the application of biological markers (e.g.: fFN, granulocyte colony-stimulating factor and alpha-fetoprotein) in predicting sPTB is Iams JD‘s main research direction[16–18].
Research Hotspots
By using CiteSpace to capture burst keywords and build the timeline view, we further explored and excavated emerging research hotspots. The recent research hotspots mainly focus on three aspects. On the one hand, the role of new ultrasound markers in predicting sPTB; on the other hand, the application of new biological markers in predicting sPTB, and finally, predicting sPTB in twin pregnancies.
Ultrasound is widely recognized as the primary method for predicting premature delivery in pregnant women[19], and the measurement of CL is the most common predictor[15, 20]. Our research indicated that the uterocervical angle (UCA) and quantitative ultrasound have emerged as research hotspots in recent years. Related studies have found that UCA performed better than CL in predicting sPTB, and UCA can serve as a useful ultrasound marker for the predicting PTB in high-risk patients[21, 22]. Conversely, one study showed that UCA was unable to predict PTB in women at risk between 20 and 31 weeks of pregnancy, while CL exhibited notable accuracy in predicting PTB[23]. Furthermore, a recent study suggested that measuring the UCA combined with CL is more accurate than measuring them separately for predicting the risk of PTB[24]. Quantitative ultrasound is a method that uses quantitative ultrasound data to reflect changes in tissue microstructure before the onset of clinical symptoms[25]. Therefore, quantitative ultrasound features could detect early cervical microstructure changes[26, 27]. And researches have demonstrated the robust consistency and repeatability of quantitative ultrasound measurements[28, 29]. A prospective study found that the quantitative ultrasound feature provided a small but statistically significant improvement in PTB risk assessment[25]. Burgos-Artizzu XP et al. found that the combination of quantitative ultrasound and CL significantly enhanced the predictive performance[30]. Overall, further validation of the predictive efficacy of these new ultrasound indicators is still needed through multicenter prospective cohort studies.
In addition to ultrasonic markers, many researchers are also committed to finding biological markers to predict sPTB. Measurement of fFN concentration in the cervicovaginal fluid is a known biological predictor of sPTB[31]. Nevertheless, several studies have indicated that fFN has limited predictive capacity for PTB, necessitating further research into alternative screening modalities[32, 33]. Our research revealed that PAMG-1 and lactobacillus iners have been the research hotspots in recent years. Transudation of PAMG‐1 occurs through chorioamniotic pores in fetal membranes during uterine contractions. Additionally, the degradation of the extracellular matrix of fetal membranes is due to the inflammatory process of labor and/or infection could allow PAMG‐1 to permeate[34]. Therefore, PAMG‐1 may be a more accurate predictor of imminent delivery. Certain researchers have observed that the predictive accuracy of PAMG-1 is comparable to that of fFN[35, 36]. However, unlike fFN, it is unaffected by recent sexual intercourse or contamination with urine, and it offers advantages of lower costs and faster testing[37]. Moreover, in the prediction of sPTB within 7 days of testing in women with signs and symptoms of preterm labor, the positive predictive value (PPV) of PAMG-1 surpassed that of fFN and CL[34, 38]. Furthermore, the combination of PAMG-1 with CL demonstrated high predictability for impending spontaneous preterm delivery in women with threatened preterm labor[36, 39]. Moreover, the vaginal microbiome plays an important role in the health of the female reproductive tract, and a Lactobacillus species-dominated microbiome has been considered important to maintain a healthy state by producing lactic acid and lowering the vaginal pH. The presence of three Lactobacillus species―L. crispatus, L. jensenii, and L. gasseri were associated with reduced risk of PTB, while the presence of L. iners was associated with increased risk of PTB[40]. Studies from different countries also showed a significant association between L. iners and an increased prevalence of sPTB[41]. In fact, there is a lot of controversy over whether L. iners is advantageous or detrimental for the host microbiota. Some studies suggested that when there is an abundance of L. iners because of its low production of lactic acid, the vaginal microflora does not maintain a low enough pH to be protective. This condition allows a higher diversity of pathological species, which leads to a higher risk of PTB[42]. Conversely, a minority of researchers found that the majority of women with an L. iners-dominated vaginal community will deliver at term without experiencing adverse pregnancy outcome[43, 44]. Due to the significant complex and diverse individual discrepancies of the vaginal microbiota, more studies are required to make clear whether L. iners can be used as a novel biomarker to detect the presence of sPTB.
Rencently, research hotspots have focused on predicting sPTB in twin pregnancies, due to the increase in the number of twin pregnancies caused by older reproductive age and the use of assisted reproductive technologies [45, 46]. The incidence of PTB in twins is ten times greater than in singleton pregnancies[47]. Consequently, precise prediction of PTB will greatly reduce the incidence of PTB in twin pregnancy and improve the physical quality of perinatal infants. Certain studies have proposed that a single measurement of CL at 20–24 weeks of gestation is a good predictor of PTB at < 28, <32, and < 34 weeks of gestation in asymptomatic women with twin gestations. However, in patients with symptoms of preterm labor, the accuracy of CL measurement in predicting PTB is limited[48, 49]. A meta-analysis found that fFN has low to moderate accuracy in predicting sPTB in both asymptomatic and symptomatic women with twin gestations[50]. In addition, the combination of fFN and CL did not notably enhance predictive performance compared to either CL or fFN alone[50]. In summary, no single screening modality for sPTB can be universally applied for women with twin pregnancies. We still need to develop new markers to improve the accuracy of predicting sPTB in women with twin pregnancies.
Overall, our study systematically analyzed the field of predicting sPTB using bibliometric tools and forecasted future research trends. This study not only aids researchers in gaining a comprehensive understanding of the advancements and evolution in predicting sPTB over the past two decades but also offers insights for their future research direction. Inevitably, our study has some limitations. Primarily, we only analyzed English-language data from WoSCC, omitting information from other crucial search engines (such as PubMed and Ovid) and different languages. Secondly, despite ongoing updates to the WoSCC database, our study encompasses the majority of articles related to predicting sPTB between 2004 and 2023, suggesting that new data might not significantly impact the outcomes. Finally, most of the information was extracted by bibliometrics software, so our results may also be biased. For example, we cannot rule out the possibility that some authors have the same acronym and some keywords have different expressions.