If the urine has a specific gravity of 1.020 or greater, the sensitivity of a urine immunologic test for pregnancy is equal to IRA of serum beta-hCG.
An intrauterine gestational sac, if present, can be reliably detected by ultrasound when the quantitative serum beta-hCG reaches 1200 mIU.
A complex adnexal mass or free fluid in the cul-de-sac seen with ultrasound and a positive pregnancy test is pathognomonic for ectopic pregnancy.
Transvaginal ultrasound will show a viable intrauterine pregnancy not earlier than 7 weeks of gestation.
An intrauterine pregnancy is reliably distinguished from the decidual reaction in the normal menstrual cycle by the presence of a double white line around the gestational sac.
The reliability of urine pregnancy tests is affected by the concentration of the urine. When a test sensitive to 25 IU/L is used, a negative test 1 week after the “missed period” virtually guarantees that the woman is not pregnant. The gestational sac can be detected by transvaginal ultrasound by approximately 5 weeks, and transabdominal at 6 weeks. The fetal heartbeat appears shortly after the sixth week. The absence of a heartbeat may indicate a missed abortion if a fetus is seen, or a blighted ovum if only a sac is present. If the serum beta-hCG is greater than 1600–1800 mIU and no intrauterine gestational sac is seen on transvaginal ultrasound, ectopic pregnancy is likely. The definitive diagnosis of ectopic pregnancy by ultrasound requires visualizing a fetus or fetal heartbeat outside the uterus.