Early pregnancy: normal and abnormal.

The understanding of early pregnancy both normal and abnormal as seen by transvaginal ultrasound is an essential skill of any clinician involved in reproductive medicine and infertility. The "sonomicroscopy" of the vaginal probe results from the high level of magnification and close proximity to the structure being studied. In addition, the ability to detect minute levels of human chorionic gonadotropin, often by over-the-counter home pregnancy tests, has caused patients to present to clinicians earlier then ever before. It is essential that the sonologist or sonographer understand what early pregnancy looks like on transvaginal ultrasound and why it looks like that, so that one can distinguish early pregnancies that are normal from those that are absolutely destined to fail. In addition, understanding the use of ultrasound and human chorionic gonadotropin in the modern diagnosis of ectopic pregnancy as well as a newly emerging category of pregnancies of unknown location is essential to clinical practice. This article will review the fundamental principals outlined above.