Experts review invisible pregnancies

The number of pregnancies that cannot be detected by scans is increasing, experts have warned.

If a scan cannot detect a pregnancy, doctors have to worry it might be ectopic – taking place outside the womb – placing the mother in danger.

The problem has occurred because women have assessments earlier in pregnancy, say Dr Haritha Sagili and colleagues from Nobles Hospital in the Isle of Man, UK.

Pregnancies of Unknown Location involve a positive pregnancy test but without any sign of a pregnancy inside or outside the womb, on ultrasound scans or even laparoscopy.

This can affect up to 31 per cent of women attending early pregnancy assessment centres, the experts write in TOG: The Obstetrician and Gynaecologist. Ectopic pregnancies must be identified they can have fatal consequences, they warn.

In their article, the authors state: “Conservative management of PUL results in lower rates of unnecessary intervention, as the condition often resolves spontaneously; the difficulty is in determining which ones will not.”

In order to identify the location of the pregnancy, women’s levels of the “pregnancy hormone” hCG can be measured. About 70 per cent of women with ectopic pregnancy will show reduced levels, or a slower rise than normal. But this approach is not sufficiently reliable.

Instead, diagnosis of ectopic pregnancy should be based on the positive detection of an extrauterine sac using transvaginal ultrasound, together with indirect signs such as a complex adnexal mass or echogenic fluid.

“In combination, these methods have a 93.5 – 100 per cent positive detection rate,” say the authors.

Journal editor, Professor Neil McClure, said: “One can’t be too careful: ectopic pregnancy is a killer. However, no one wants to operate unnecessarily – just in case it might be an ectopic pregnancy: the secret is very careful assessment and water-tight review processes to ensure that patients are not lost from follow-up”.

Sagili, H. and Mohamed, K. Pregnancy of unknown location: an evidence-based approach to management. The Obstetrician & Gynaecologist, Vol. 10, Issue 4, 2008, pp. 224-30.