In this study, we collected the demographic and ultrasound findings for days 27-29 after ET and constructed a simple scoring system for the prediction of EPL, with AUCs of 0.884 and 0.878 in the training set and verification set, respectively. Point 5 had the highest predictive accuracy and was recommended as the cutoff value for clinical practice.
The process of achieving pregnancy through IVF is usually very difficult for an infertile woman. Thus, when the woman becomes pregnant by IVF, she is usually very anxious about the development of the embryo, even after the detection of cardiac activity but especially if an empty gestational sac or only a YS are detected. Generally, for patients who have well-developed embryos at the first routine TVS examination on days 27-29 after ET, the next ultrasound scan will usually be scheduled on day 45 after ET; however, for patients with embryos of uncertain viability, the recommendation is usually to have another TVS scan 7-10 days after the first scan to assess the development and viability of the embryo.
If the pregnancy outcome can be predicted in advance, the anxiety of the pregnant woman can be greatly relieved. Many models have been constructed to predict pregnancy outcomes effectively[13][14][15]. Among them, LR analysis has been the most commonly used[15][16]. While what we want to construct is a simple and practical scoring system that is similar to the “Apgar score system” using simple demographic and ultrasound findings on days 27–29 after ET, as this would be easy for clinical application, especially for patients without sufficient assisted reproduction indicators when they return home after pregnancy, and this is why we performed this research. Through this system, we can inform patients with a specific probability of miscarriage after the first routine TVS examination, which may help reduce the patient’s anxiety and psychological burden and provide guidance for follow-up decisions.
The findings of this study agree with our current knowledge that miscarriage is more likely with increasing MA[17], low hCG level[18], low EM thickness on transfer day[19] and the presence of IUH[20] and that miscarriage is less likely after the visualization of embryonic cardiac activity[15]. Accordingly, in our scoring system, a greater MA was associated with a higher point, while greater GSD, YSD, EL and EHR were all related to lower points. However, both small and large YSDs corresponded to higher points. A higher point means a greater contribution to miscarriage. Thus, the possibility of miscarriage increased with the total score. Point 5 offered the highest predictive accuracy in both the training set and verification set, and the corresponding miscarriage risk exceeded 30%, which was not a low risk for anxious IVF patients. Therefore, we recommend using point 5 as a clinical threshold for warning patients of this risk counselled more about miscarriage. In practical applications, we hope that the false positive rate (FPR) will be as low as possible, as this may lead to unnecessary medical treatment. A low FPR requires high specificity. In this system, the specificity of points -8 to 0 was not satisfactory. Thus, this is a scoring system for determining the probability of miscarriage that could allow doctors and patients to know the risks in advance, but because miscarriage cannot be prevented, the outcome cannot be changed by this scoring system. The advantage of this scoring system is that it is easily transferable to clinical use, where both maternal and ultrasound variables are easily available and the calculation is quite easy. For example, in a woman whose MA = 38 yr and who has an EM = 8 mm on transfer day, a GSD = 10 mm, a YSD =2.2 mm, and an EHR = 88 bpm by TVS on day 28 after ET, the miscarriage score is 9, and the estimated risk of miscarriage is 70.67%. Even though the results indicate a strong likelihood of EPL, there is still a significant risk that this is a false positive finding. Thus, it is imperative to repeat the ultrasound scan for this patient 7-10 days later to confirm the viability of the embryo before any medical interventions. In contrast, if a patient does not present with any symptoms and has a low total score (for example, point 0), no TVS scan is needed until day 45 after ET.
A previous study[21] constructed a similar scoring system to predict pregnancy viability and achieved an AUC of more than 0.90. However, this study focused on natural conceptions, and the ultrasound variables and clinical characteristics collected in that study were collected within a time period of GA <84 days. The measurement methods may also differ from ours. However, in our study, all ultrasound parameters were collected at the same time on days 27-29 after ET, and the specific EHR value was included, not just the presence or absence of embryonic cardiac activity. IUH was unexpectedly not included in the final system. We speculate that this may be because IUH occurs more frequently in pregnancies after IVF than in spontaneous conceptions[22], not only in women with EPLs but also with ongoing pregnancies.
We note that the sensitivity of this simple model was not ideal, which might indicate that for the IVF population, only including ultrasonic measurements and simple clinical indicators had limited predictive efficacy, and in further study, relevant indicators for assisted pregnancy should be added to improve the predictive efficacy. Another limitation was that since there was no information on bleeding, abdominal pain and smoking history in our hospital's electronic medical record system during the study period, these indicators were not included in our system, but might further improve the predictive performance if included. Since this system was derived from the IVF population, its application in the general population had yet to be validated.
In conclusion, we have developed a simple and practical scoring system that provides a probability for EPL based on the simple demographic and ultrasound findings obtained on days 27–29 after ET. This system is easy and simple for clinical use. Point 5 is recommended as the clinical threshold for warning patients of an EPL risk. When the predictive result is a high risk of EPL, repeated scans are recommended 7-10 days later to confirm the viability of the embryo. When the predictive result is a low risk of EPL and patients have no symptoms, the next examination can be performed on day 45 after ET.