Objectives: To assess the safety and performance of the M4 model for classifying as high risk or low risk for ectopic pregnancy (EP) pregnancies conceived by assisted reproductive technologies (ART) that present with low beta-human chorionic gonadotropin (β-hCG) concentration in early gestation.
Methods: This was a prospective cohort study of 243 pregnancies conceived by ART with low β-hCG levels (5-50 IU/L) at 4 + 0 to 4 + 2 weeks' gestation. After subsequent β-hCG testing at 48 h, pregnancies were classified according to the M4 model into the following categories: (i) high risk, probable EP/persistent pregnancy of unknown location (PPUL), when the risk for EP was ≥ 5%; (ii) low risk, probable intrauterine pregnancy (IUP), when the risk of EP was < 5% and the likelihood of IUP was greater than that of a failed pregnancy of unknown location (FPUL); and (iii) low risk, probable FPUL, when the risk of EP was < 5% and the likelihood of a FPUL was greater than that of an IUP. The predictive performance of the M4 model for EP and its ability to discriminate between high- and low-risk pregnancies was assessed using the final pregnancy outcome at 11 to 13 weeks of gestation as reference, which was classified as EP/PPUL, FPUL or IUP.
Results: The sensitivity and specificity of the M4 model in detecting a high-risk pregnancy (EP/PPUL) were 60.0% (95% CI, 43.6-74.4%) and 79.8% (95% CI, 73.8-84.7%), respectively. The area under the receiver-operating-characteristics curve of the M4 model for discriminating between high-risk and low-risk (FPUL/IUI) pregnancies was 0.72 (95% CI, 0.62-0.81). The model had a positive likelihood ratio of 2.97 (95% CI, 2.03-4.36) and a negative likelihood ratio of 0.50 (95% CI, 0.33-0.76). The kappa index was 0.30 (95% CI, 0.16-0.43), indicating a low degree of agreement between the model classification and the final diagnosis. No serious adverse events related directly to the application of the M4 model were observed, although 14 pregnancies classified ultimately as high risk had been categorized initially as low risk by the M4 model. Of these, seven resolved with expectant management, five with methotrexate (MTX) and two required laparoscopic surgery (one after failure of medical treatment with MTX and one after deviation from the follow-up protocol). There were no cases of EP/PPUL with additional complications or need for blood or other blood product transfusion. Of the 243 ART pregnancies with low β-hCG concentration in early gestation, only 47 (19.3%) had an IUP, half (24/47) of which had an early miscarriage, resulting in only 9.5% (23/243) cases having an ongoing pregnancy.
Conclusions: Application of the M4 model in pregnancies conceived by ART with low β-hCG concentration in early gestation showed limited capacity in classifying them as being at low or high risk for EP, therefore, its use in pregnancies of this type is not recommended. No serious adverse events or complications related to the use of the model were observed. These pregnancies have a low probability of ending in an IUP as well as a high rate of early miscarriage. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.
Keywords: assisted reproductive technology; ectopic pregnancy; infertility; pregnancy of unknown location; triage.
© 2021 International Society of Ultrasound in Obstetrics and Gynecology.