An ultrasound scan done in early pregnancy is supposed to bring clarity as to whether a pregnancy is vital or not. The determinant cut-off values reported in literature for the chorionic cavity diameter (CCD) are between 13 and 25 mm and between 3 and 8 mm for the crown-rump length (CRL).
Percentage of false-positive abortion diagnoses
Yazan Abdullah and his colleagues have now investigated the percentage of false-positive abortion diagnoses for 1060 women carrying a pregnancy in which its vitality was in doubt (ie. there was doubt as to whether the embryo was alive or not). Uncertainty relating to vitality was declared, in instances where only an empty gestational sac was shown, or a gestational sac with a yolk sac without an embryo, if the chorionic cavity size was less than 20 mm or less than 30 mm, or in instances with an embryo without a heartbeat where the CRL was less than 6 mm or less than 8 mm.
Of the 1060 women with a pregnancy indicated at first as uncertain, at least 473 had a vital pregnancy, indicated as such in the 11th to14th week. For 587 women the pregnancy was nonvital. A false-positive rate (FPR) in relation to the diagnosis “delayed miscarriage” was found for 4.4% of women, when embryo and yolk sac were missing and a chorionic cavity size cut-off point of 16 mm was used. The FPR was 0.5% for a chorionic cavity size cut-off point of 20 mm. There were no false-positive results when the CCD cut-off value employed was larger than or equal to 21mm.
Women given the “delayed miscarriage” diagnosis (as a FPR) in cases where there was a visible yolk sac without an embryo amounted to 2.6%, when the chorionic cavity size cut-off value was 16 mm. Only for a chorionic cavity size cut-off greater than or equal to 21mm were there no more false-positive diagnoses.
If the embryo was visible, but no heartbeat detectable, the FPR was found to be 8.3%, when a CRL cut-off value from 4 mm to 5 mm was used. There were however no false-positive results for a CRL cut-off value of 5.3 mm or greater.
These results show that the current cut-off values are unsafe for use, say the authors. They propose that a chorionic cavity diameter cut-off value of greater than 25mm, and a CRL cut-off value of greater than 7 mm, be set, in order to minimise the risk of false-positive diagnosis.
Deciding to wait
How great the emotional burden of the parents is, when the diagnosis “missed abortion” is given, is something a father named “Oli” describes very starkly on the Internet. The beauty of his case is that, on the day on which his wife’s abrasion should have taken place, the ultrasound revealed a living fetus with a beating heart. The best way to avoid that, in instances of false-positive diagnosis, living fetuses end up being removed, is to wait. Approximately 15% of clinically detected pregnancies end in abortion. The possibility of a straightforward outcome, whether one waits or has an abrasion, is about the same, according to authors Alexandra Molnar et al. from the University of Washington, Seattle. They asked 75 women aged between 18 and 45 about which course of action they would wish to undertake in case of a diagnosis of “delayed miscarriage”. 27 of the women surveyed had already experienced spontaneous abortions. The survey results: 72% of respondents would opt to wait – there was no percentage difference between women who had already experienced an abortion and those who had not previously had a miscarriage. Half of the women said however they would in an emergency choose to take the advice given by the gynaecologist.
Apparently it’s therefore not so that women, with a non-vital pregnancy – after the initial shock – “seek as soon as possible to get it done and over with”. Many women apparently rather want to wait and see out a natural termination of pregnancy. At the same time, this approach is the best protection against the unwanted consequences of a misdiagnosis.