What is the gestational sac?
The gestational sac is the embryonic vesicle, the fluid sac in which the embryo is found. The gestational sac can be seen usually by transvaginal ultrasound once it reaches 2 to 5 mm in diameter, which occurs at the age of approximately 5 weeks gestation (ie, 3 weeks after conception).
What happens if the pregnancy test is positive but the gestational sac does not appear?
Factors such as ultrasound scan resolution, uterine orientation, and the presence or absence of fibroids affect when and in what size the sac becomes visible. Sometimes, you do not see yourself at the first ultrasound. Therefore, do not be alarmed.
From the 1980s, several authors attempted to determine the concentration of maternal beta hCG above which a gestational sac should be visible on ultrasound. For transvaginal ultrasound, the level of hCG is 1000-2000 mIU / mL. If the gestational sac is not seen on ultrasound with more than 2000 mIU / ml of hCG, the possibility of an ectopic pregnancy begins.
If a woman with a hCG level above 1500 or 2000 mIU / mL and does not have an ultrasound-visible intrauterine gestation is presumed to have an ectopic pregnancy or abortion and is treated with methotrexate or dilatation and curettage. The problem is that this criterion the criterion is not 100% reliable and it can be wrongly interrupted a normal gestation.
This criterion has been questioned in several studies suggesting that the level of discrimination is not entirely reliable. There are women with a β-hCG above 2000 mIU / mL and up to 4000 mIU / mL who do not show an intrauterine gestational sac on the transvaginal ultrasound and yet show viable pregnancies on subsequent ultrasound scans.
Therefore, a single measurement of the level of hCG and a single ultrasound scan should not be used to determine ectopic pregnancy. Several ultrasound scans and several measurements of beta hCG in series should be made before assuming that there is no viable pregnancy.