Each stage of pregnancy has characteristics that are fairly reliable indicators of whether the fetus is healthy and developing as it should. That's one reason why ultrasounds can be so valuable, even in the firstweeks.
If you have an early ultrasound, which might happen around 6 weeks, the doctor and technician will look for a yolk sac. When this vital structure doesn't appear, the most likely reason is that the pregnancy isn't viable—in other words, a miscarriage has occurred.
That said, miscarriage isn't the only possibility. If you're newly pregnant and the yolk sac isn't visible on your 6-week ultrasound, it may simply mean you aren't as far along as you thought. Here's what to know about either possibility.
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What Is the Yolk Sac?
In early pregnancy, the yolk sac functions as a source of nourishment for the developing fetus, before the placenta is fully formed. It's the first structure to be visible withinthe gestational sac, whichenvelopesthe developing fetus and theamniotic fluid.
The gestational sac looks like a white rim around a clear center. It can be seen on a transvagin*l ultrasound—a procedure in which the ultrasound wand is inserted into the vagin* rather than pressed against the abdomen—around 4.5 to 5 weeks gestation.The yolk sac might not be visible until around 5 weeks post-fertilization (7 gestational weeks).
The yolk sac provides nutrition to the developing embryo until the placenta takes over. That's why it's a good indicator of the health of the pregnancy.
Why Is There No Yolk Sac?
No yolk sac at 6 weeks could indicate a miscarriage, but it could also mean you miscalculated your due date. Here's what to know.
Miscalculated due date
Occasionally, not seeing a yolk sac on an ultrasound in early pregnancy could simply meanthe gestational age was miscalculated. This might happen if you misremembered the date of your last menstrual period or if you have irregular menstrual cycles.
When a doctor suspects incorrect gestational age in a person who was believed to be around 6weeks pregnantbut has no yolk sac, they usually recommend doing another ultrasound in a week or two. By then, if all is well and the pregnancy is viable, the yolk sac and possibly the fetal pole (a curved structure that will eventually develop into the baby) will be visible.
No Yolk Sac at 5 to 6 Weeks
No yolk sac at 5 to 6 weeks of gestation may mean either that the pregnancy is less than 6 weeks along or there's been a miscarriage. Having another ultrasound in one or two weeks can determine if the pregnancy is viable or not.
Sign of miscarriage
Sometimes, seeing no yolk sac (or a yolk sac that is smaller than expected or otherwise misshapen) at 6 weeks can be a sign of miscarriage. Unfortunately, you'll most likely have to wait for a follow-up ultrasound to be sure. At that time, if the ultrasound doesn't show continued development of the pregnancy and there's still no visible yolk sac, your doctor will diagnose a miscarriage.
You won't always have to wait, however. If the gestational sac is a certain size (25 millimeters or more) on the first ultrasound and there's no yolk sac or embryo, your doctor might diagnose a miscarriage right away.
Empty Sac Pregnancy
When the gestational sac is empty (meaning there's no yolk sac or embryo at the expected time), this is known as an empty sac pregnancy. Other terms for an empty sac pregnancy are an"anembryonic" pregnancy or a blighted ovum.
An empty sac pregnancy is a type of miscarriage, even though the products of conception are still contained in the uterus. If this happens, youmay be given the choice of letting nature take its course, taking medication, or having a procedure called dilation and curettage (D&C), which involves dilating the cervix to create an opening for a thin surgical instrument to remove tissue from the uterus.
Research shows that empty sac pregnancies frequently have chromosome abnormalities. It's believed that the body recognizes the problem and stops further progress of the pregnancy.
Key Takeaway
Not seeing the yolk sac at the pregnancy confirmation appointment can be scary and disappointing. Sometimes, the due date calculation might be off, so you could still be pregnant. Other times, the yolk sac is absent due to a miscarriage. Rest assured that early miscarriages are very common, often happening before someone even knows they're expecting—and having a marriage in no way indicates that you won't carry to term next time.
