The optimal timing of an ultrasound scan to assess the location and viability of an early pregnancy.

BACKGROUND The objective of this study was to determine the optimal gestational age at which to establish the location and viability of an early pregnancy using transvaginal ultrasonography (TVS). METHODS This was a prospective study of 1442 women undergoing initial TVS at no more than 84 days gestation. Logistic regression analysis was performed to determine the relationship between gestational age and the ability to confirm viability or non-viability, in women with and without symptoms of pain and bleeding. RESULTS The commonest TVS finding prior to 35 days was a pregnancy of unknown location, from 35 to 41 days an early intrauterine pregnancy of uncertain viability and from 42 days a viable intrauterine pregnancy. Miscarriage could only be diagnosed on initial TVS after 35 days. There was no difference between the ability to make a diagnosis for women with certain or uncertain dates (P = 0.719). The chance of confirming viability increased rapidly per day of gestation until 49 days and thereafter plateaued. Of the 29 ectopic pregnancies diagnosed, 72% presented prior to 49 days gestation and all of these women presented with pain, bleeding or a previous ectopic pregnancy history. CONCLUSIONS The ability to confirm viability or non-viability is significantly related to gestational age. In asymptomatic women with no previous ectopic pregnancy TVS should be delayed until 49 days. Our data suggest that this would reduce the number of inconclusive scans, without an associated increase in morbidity from missed ectopic pregnancies.