Regardless of the level, if any, of assisted reproduction, the use of ultrasound in early pregnancy begins with basic physiology and anatomy. Most often, the patient with an issue of questionable fertility is well-known to the medical establishment, highly motivated, compliant, and usually follows any instruction offered. More often than not, the biochemical evidence of a pregnancy event (i. e. , detection of human chorionic gonadotropin in blood or urine) precedes our ability to see the pregnancy sonographically.
In fact, the gap between biochemical detection (as early as 30 to 50 mIU/mL) often from over-the-counter home pregnancy tests and our ability to detect a pregnancy even with the sonomicroscopy of the vaginal probe has widened in the recent past. Human chorionic gonadotropin (hCG) is produced by trophoblastic tissue. It is detectable 8 days after conception.  Conventional over-the-counter home pregnancy tests turn positive at around the time of the missed menses (30 to 50 mIU/mL). It is often erroneously referred to as the "beta subunit" or simply the "beta" although most current tests measure the intact hCG molecule.
The ? subunit was originally described to distinguish it from the ? subunit, something that is shared with other molecules such as thyroid stimulating hormone (TSH). Normally, hCG doubles every 48 hours, although a minimum rate of rise is 53 to 66%[2,3] in 48 hours. It is essential to realize that apparently normal doubling times of hCG do not ensure an intrauterine location, as 15 to 20% of ectopic pregnancies can follow normal doubling times of hCG, and these are ones that often end up with a beating heart and normal appearance, although extrauterine in location