Otherwise an 18 week ultrasound examination is adequate for confirmation of dates. However, the success of early transabdominal and transcervical chorionic villus sampling depends upon the reliable identification of placental location and detection of embryonic cardiac activity using high resolution ultrasound. If amniocentesis is performed in the first trimester, ultrasound monitored technique adds to the ease and expediency of the amniocentesis and reduces the frequency of bloody and dry taps and multiple needle insertions. In selective reduction of multi-fetal pregnancies colour flow imaging can delineate all the vascular connections between siblings in utero and aid in directing the reduction procedure. At this time no recommendation can be made to support or refute the use of ultrasound in the management of threatened spontaneous abortion.
Threatened abortion is usually the most common perceived indication for first trimester ultrasound.
28-29 Bleeding in early pregnancy without abdominal pain and cervical dilation can cause intense anxiety for the woman and some degree of clinical uncertainty for the physician. Women having experienced vaginal bleeding in the first trimester can be reassured by having a scan and seeing a live fetus moving. Conversely, absence of fetal heart activity allows the woman to dissociate herself from the non-viable fetus. 32 Women with vaginal bleeding, accompanied by pain and passage of blood clots, are likely to have evidence of a dilating cervix. Pelvic examination may permit immediate diagnosis of an evolving miscarriage.