What is the gestational sac?
The gestational sac (in English gestational sac) is the first structure observed in early pregnancies. It appears as a small round cavity filled with fluid, located within the uterus. Its presence is crucial because it indicates that the pregnancy is intrauterine (therefore correctly positioned) and not ectopic. Following the gestational sac, the following develop:
- the yolk sac,
- the embryo,
- and finally the amniotic cavity.
Gestational sac and first ultrasound Most women have their first ultrasound between the 5th and 7th week of pregnancy, after a positive test. 📌 Generally, the gestational sac is visible when the beta-hCG levels in the blood reach about 1500 UI/ml. During the ultrasound, the gynecologist assesses:
- the position of the sac in the uterus;
- its size;
- the presence of one or more sacs.
If the beta-hCG levels are high but the sac is not visible in the uterus, there may be a suspicion of ectopic pregnancy. Size of the gestational sac The growth of the gestational sac follows fairly precise parameters and is often used to estimate gestational age:
- 1–4 mm → 4th/5th week of pregnancy
- 5–8 mm → 5th/6th week of pregnancy
The sac grows on average 1–1.2 mm per day.
⚠️ If the average diameter exceeds 20 mm without the embryo being visible, it is referred to as a empty gestational sac (anembryonic sac), a condition that unfortunately indicates a high risk of miscarriage. Empty gestational sac: what does it mean? An empty gestational sac is a pregnancy in which the embryo does not develop, despite the presence of a yolk sac and amniotic cavity. The most common causes include:
- chromosomal and genetic abnormalities,
- immunological issues,
- early infections.
This condition inevitably concludes with a miscarriage. It is important to emphasize that an empty gestational sac does not increase the risk of miscarriages in future pregnancies. ❓ FAQ – Gestational sac
- When is the gestational sac visible?
Usually between the 4th and 5th week of pregnancy, when beta-hCG levels exceed 1500 UI/ml.
- What does an empty gestational sac mean?
It indicates a non-viable pregnancy, in which the embryo has not developed or has been reabsorbed.
- What are the normal sizes of the gestational sac?
At the 4th-5th week it measures about 1–4 mm, at the 5th-6th week 5–8 mm, with an average growth of 1 mm per day.
- What happens if the sac grows but the embryo is not visible?
If the sac exceeds 20 mm without an embryo, it is referred to as an anembryonic sac, a condition that leads to miscarriage.
- Does an empty gestational sac affect future pregnancies?
No, it typically does not increase the risk of subsequent miscarriages. Conclusions The gestational sac is the first visible sign of a pregnancy and its ultrasound evaluation is essential to confirm correct intrauterine localization. However, its mere presence does not guarantee that the pregnancy is viable: for this reason, careful medical monitoring is always necessary. Note: The contents of this page are for informational purposes and do not replace professional advice. In case of symptoms, doubts, or medical needs, always consult a qualified physician.
