Ultrasound follow‐up in the first trimester when pregnancy viability is uncertain

Miscarriage is a common complication of pregnancy affecting up to one in four clinical pregnancies. Ultrasound is the diagnostic tool of choice when evaluating not only pregnancy gestation and location but also pregnancy viability. Mean gestational sac diameter (MSD) and crown‐rump length (CRL) are used to diagnose miscarriage. Experienced operators using high resolution transvaginal ultrasound (TVS) can make a diagnosis of a missed miscarriage when there is the presence of a CRL measuring >7 mm with no embryonic heart rate (EHR) present.1 The diagnosis of an empty sac miscarriage can be made when there is an empty intra‐uterine gestational sac (GS) present with a MSD of >25 mm.1 In both instances, the absolute level of serum human chorionic gonadotrophin (hCG) does not influence the diagnosis. It is important to note that in the presence of an ultrasound diagnosis of miscarriage (per the previously mentioned definitions), serum hCG levels can continue to increase.

A couple's desire to confirm pregnancy viability can often mean that an early TVS, even in the most experienced hands, can be inconclusive. When pregnancy location is confirmed to be intra‐uterine using TVS, if the CRL measures less than 7 mm or there is the presence of an empty GS with a MSD <25 mm, these women are classified with an intra‐uterine pregnancy of uncertain viability (IPUV).2 Importantly, when the primary scan demonstrates a ‘live’ intra‐uterine pregnancy, previously formulated algorithms have predicted an 8% chance of subsequent miscarriage.3, 4 The later the gestation at first presentation, the lower the rate of subsequent pregnancy loss.5

It is recommended that women with an IPUV are rescanned in 10–14 days’ time to assess for interval change in the ultrasound parameters and confirm pregnancy viability or non‐viability (NICE guidelines).1 However, this recommendation is not evidence based, but rather based on expert opinion and consensus. In 2013, a review in the New England Journal of Medicine based on a consensus meeting of the United States Society of Radiologists in Ultrasound highlighted the risks of incorrectly diagnosing early pregnancy failure and recommended criteria to diagnose miscarriage. In the absence of an embryo with a heartbeat ≥14 day after a scan showing an empty GS or absence of an embryo heartbeat ≥11 days after a scan showing a GS and yolk sac were both categorically a miscarriage.6 These couples are left waiting for up to 2 weeks in a state of uncertainty, and this can be extremely psychologically distressing. Is there any way that can give these couples an answer with respect to the viability of their pregnancy without the agonising wait?

The initial article that instigated the changes in miscarriage criteria was as follows: ‘Limitations of current definitions of miscarriage using mean gestational sac diameter and crown–rump length measurements (CRL): a multicenter observational study’ by Abdallah et al.7 After that study in 2011, cut‐off values to define miscarriage using ultrasound changed; however, the data supporting this change had wide confidence intervals.

Several reviews of this initial article raised concerns regarding the study design as well as the potential for false‐positive diagnoses of missed miscarriage despite the revised criteria. Ross et al. raised concerns about the conflicting information regarding the study type and the lack of histological diagnosis of miscarriage as well as the varying quality of ultrasounds at the different sites. There was concern that some of the scanning quality may have been below average.6 Another criticism of the initial study was that regardless of the new criteria, there would continue to be misdiagnoses of miscarriage due to false‐positive findings. While Jurkovic acknowledges that occasional diagnostic errors are accepted and unavoidable, when it comes to miscarriage, even one misdiagnosis is unacceptable. The best approach to avoiding such a situation would be ‘never in one visit and never by one person’.8 Comments such as these may limit using ultrasound findings in isolation at one visit to diagnose a miscarriage in women who have IPUV.8

When these cut‐offs to define, non‐viability are not met, it is not unreasonable to utilise a multicategorical algorithm. While such an approach may not give a definitive diagnosis at the initial visit, it may assist in counselling women and couples can be given an individualised likelihood of the pregnancy continuing. Several scoring systems have been developed to individualise early pregnancy counselling and incorporate it into early normal pregnancy care. Bottomley et al. developed a scoring system to assess whether an IPUV will continue to be an ongoing viable pregnancy by the end of the first trimester. Age, bleeding score, gestational age, mean gestation and yolk sac sizes and the presence of EHR were the factors that gave the most accurate prediction of viability. The area under the receiver operating characteristic curve (AUC) of 0.954 shows that the model performs well. It did not give an indication about the outcome on viability and miscarriage.9

In 2015, a multicentre prospective UK study validated the 2011 cut‐off values for embryo CRL and MSD to diagnose miscarriage with high levels of certainty.10 The authors demonstrated that on the initial scan an empty GS of MSD ≥ 25 mm was 100% specific for miscarriage, as was an embryo with no heart activity and a CRL ≥ 7 mm. Additional non‐viability criteria at the initial scan included the following:

• Beyond 70 days gestation, an MSD ≥ 18 mm with no embryo was 100% specific for miscarriage as was an embryo with CRL ≥ 3 mm with no heart activity.10

For repeat scans:

• a pregnancy with an embryo with no heart activity on initial scan and a repeat scan ≥7 days later was 100% specific for miscarriage;

• a pregnancy with no embryo and an MSD <12 mm if sac size had not doubled after ≥14 days was also 100% specific for miscarriage; and

• a pregnancy with no embryo and an MSD ≥ 12 mm with no embryo heart activity after ≥ 7 days were also 100% specific for miscarriage.10

Currently, TVS is used to assess the viability of first‐trimester pregnancy. The ultrasound cut‐offs for defining miscarriage have been prospectively validated. Furthermore, the timing of subsequent ultrasound scans in women with an IPUV has been outlined. The implementation of these timings for the second scan in women with uncertain pregnancy viability now need to be prospectively validated to ensure that no woman with a potentially viable intra‐uterine pregnancy is wrongly classified as non‐viable.