What Does It Mean If There's No Yolk Sac At 6 Weeks?

This Could Be a Sign of an Earlier Viable Pregnancy or a Miscarriage

pregnancy ultrasound
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When an ultrasound shows no yolk sac at 6 weeks, there could be two explanations. Although it could mean a miscarriage has occurred, it's also possible that the pregnancy is simply earlier than previously thought.

What Is the Yolk Sac?

In early pregnancy, the yolk sac functions as a source of nourishment for the developing fetus before ultimately being absorbed by the fetus as a part of the gut. The yolk sac is the first thing to become visible inside the gestational sac on a transvaginal ultrasound, appearing at an average of 5.5 to 6 weeks gestational age.

What Does It Mean If There's No Yolk Sac At 6 Weeks?

Because the yolk sac first becomes visible around 5.5 weeks of gestation, seeing no yolk sac on an ultrasound around that time could simply mean that the pregnancy is not actually that far along.

In other words, your fetus' gestational age could have been miscalculated. This can happen if you made an error in remembering your last menstrual period or if you have irregular menstrual cycles.

When doctors suspect incorrect gestational age in a woman who was believed to be around 6 weeks pregnant but has no yolk sac, they will usually recommend a second ultrasound.

In a viable pregnancy, the yolk sac and possibly the fetal pole will be visible on a follow-up ultrasound.

When It's a Sign of Miscarriage

Unfortunately, seeing no yolk sac at 6 weeks can also be a sign of miscarriage.

When you are faced with an ultrasound that shows no yolk sac, you will probably be told to wait for a follow-up ultrasound.

The wait can be very difficult, naturally, but is necessary for an accurate diagnosis. If a follow-up ultrasound does not show continued development and the appearance of a yolk sac, your doctor will diagnose miscarriage.

Or, if the gestational sac is larger than 13 mm on the first ultrasound and there is no yolk sac, you doctor may diagnose miscarriage right away.

 Research suggests that a gestational sac larger than 13 mm that contains no yolk sac is not a viable pregnancy.

Blighted Ovum - An Empty Sac Pregnancy

When the gestational sac is empty - meaning there's no yolk sac or embryo by the time there should be - it's known as an empty sac pregnancy. An empty sac pregnancy may also be referred to as an anembryonic pregnancy or a blighted ovum, although the term blighted ovum is now considered by some doctors to be outdated. 

An empty sac pregnancy is a type of miscarriage, even though the products of conception are still contained in the uterus. If this happens to you, you will probably have the choice to let nature take its course or to have a D&C to move things along faster. 

Research shows that empty sac pregnancies tend to have high levels of chromosome abnormalities. It's believed that the woman's body recognizes the problem early on and stops further progress of the pregnancy. An empty sac diagnosis may feel cruel, but you may want to think of it as nature's way of keeping unhealthy pregnancies from continuing.

According to the American Pregnancy Association, blighted ovum causes 50 percent of first trimester miscarriages. Fortunately, this is usually a random one-time event, and most women who experience it can go on to have normal pregnancies. 

Sources:

Spontaneous abortion: Risk factors, etiology, clinical manifestations, and diagnostic evaluation. UpToDate. February 23, 2015.

Blighted Ovum. American Pregnancy Association. August 2015.

Concerns Regarding Early Fetal Development. American Pregnancy Association. 

Perriera L and MF Reeves. (2008). Ultrasound criteria for diagnosis of early pregnancy failure and ectopic pregnancy." Semin Reprod Med.

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