Have you ever wondered how life begins its very first chapter inside the womb? Before a baby develops organs, bones, or even a heartbeat, there’s a tiny yet powerful structure quietly working behind the scenes- the yolk sac.
Think of it as nature’s first “life-support system,” nourishing and protecting the growing embryo long before the placenta takes over. Fascinating, right?
Continue reading to know all about the pregnancy yolk sac and find out what it means if it appears irregular or is not visible at all.
What Is the Yolk Sac in Early Pregnancy?
The yolk sac is a small, circular structure that appears like a pouch attached to the embryo in the earliest stages of pregnancy. It can usually be seen on a transvaginal ultrasound around 5.5 to 6 weeks of gestation.
Its size is usually 3 to 5 millimetres in diameter from one inside rim to the other.
What Does it Do?
This tiny sac contains nutrients and helps nourish the embryo through the following functions:
- makes red blood cells for the circulatory system of the embryo,
- helps with the circulation of gases between the mother and the embryo,
- provides early immune function and metabolism.
When does the yolk sac disappear in early pregnancy? This sac helps nourish the embryo and slowly disappears between 14 and 20 weeks of gestation. After that, the placenta takes over the role of nourishment as a part of healthy foetal development.
According to the Current Health Sciences Journal, the yolk sac is a critical indicator of early pregnancy viability. Its presence is a good sign, meaning that the pregnancy is progressing normally. It helps doctors differentiate between normal and abnormal pregnancies.
The Pregnancy Sac at 6 Weeks: Present Vs. Absent
Looking at the ultrasound of the embryos by the 6th week of pregnancy, you will notice the yolk sac that is:
- Round and well-defined sac attached to the embryo.
- You may also notice a tiny fetal pole or even a flicker of a heartbeat at this stage.
Could there be more than one sacs? Yes. In fact, two or three sacs mean that you have twins or triplets.
But what if you see no Yolk Sac in early pregnancy, should you worry?
If it is not present, the doctor may suggest waiting a few more weeks and repeating the ultrasound, as the timing can vary based on ovulation and implantation.
In some cases, an empty gestational sac without a yolk sac could indicate a blighted ovum (a type of early miscarriage).
Irregular Yolk Sac in Early Pregnancy: What Does It Mean?
Mere presence of this sac is not enough, its shape also matters. Having an irregular sac, too large, too small, or abnormally shaped, is strongly linked with a high risk of miscarriage or chromosomal abnormalities.
But it is worth noting that not all irregularities necessarily lead to complications. As per StatPearls, healthy pregnancies can occur even with oval-shaped and enlarged sacs, though it is not very common.
Based on these findings, additional clinical tests are needed to assess the embryonic health before drawing conclusions.
Read More: Mask of Pregnancy: Why It Happens and How to Manage It
To Sum Up
A yolk sac is one of the first visible structures that can be seen during prenatal ultrasound. Understanding the role of this sac can offer a sense of clarity during those crucial early weeks.
Always schedule screenings with your healthcare provider if you have concerns about your ultrasound results. And remember, one scan rarely tells the whole story. Your doctor may recommend additional imaging or tests to get the most accurate picture of your baby’s development.
