My Ultrasound Showed No Fetal Pole. Am I Miscarrying?

Fetus at 5 weeks
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A fetal pole is the earliest sign of an embryo in an early pregnancy ultrasound before the baby has formed a recognizable human shape. 

Certainly, it can be unnerving to go in for an early pregnancy ultrasound and be told there is no fetal pole or an "empty gestational sac." Obviously, it would be far more reassuring to see a baby developing right on schedule for what was expected, and ideally with a strong fetal heartbeat.

But having no fetal pole does not automatically mean miscarriage.

Let's explore this question in a bit more detail.

Fetal Pole Basics

The origin of the term fetal pole comes from the use of "pole" to describe one of two morphologically different areas at the ends of an axis in an organism.

In a newly developing baby, the fetal pole appears as a thick area on the side of the yolk sac, so it's a "pole" that is different from the rest of the yolk sac, and this "pole" will ultimately become a fetus (baby).

Around the same time that a fetal pole is identified on ultrasound, a fetal heartbeat may also be found.

While a fetal pole in no way resembles the human being a baby will become, the structure has a curved appearance, with the head of the embryo at one end and what appears to be a tail-like structure at the other. Thanks to this, a fetal pole is now used to measure crown-to-rump length (CRL), which helps date a pregnancy more accurately.

In fact, according to the American Pregnancy Association, when the CRL reaches 2 to 4 millimeters, the fetal pole is generally visible with a transvaginal ultrasound, and when the CRL reaches 5 millimeters, a heartbeat can usually be detected. 

A Missing Fetal Pole 

When a vaginal ultrasound fails to find a fetal pole or heartbeat at the expected gestational time, it can be due to a couple reasons.

Incorrect Dates

First, the estimation of pregnancy dates can be incorrect, and the structures may not yet have developed.

Remember, the fetal pole becomes visible in a transvaginal ultrasound somewhere between five and a half to six and a half weeks of gestational age. So any small error in dating the pregnancy can throw an ultrasound interpretation off because the early pregnancy development varies so much from one day to the next.

For example, if you incorrectly remembered your last menstrual period date, that can change the expected findings on an ultrasound. Or if you have an irregular cycle and do not ovulate two weeks after the start of your last menstrual period, your pregnancy may not technically be five or six weeks along—even if it has been five or six weeks since your last menstrual period.

If there is any possibility that the ultrasound shows no fetal pole because of an error in dating the pregnancy, the doctor will usually ask the woman to come in for another ultrasound in a week or two.

This wait can be understandably difficult but is necessary to avoid misdiagnosis of a miscarriage. If the problem was with the dates, the follow-up ultrasound should show continued development with a larger gestational sac and most likely the appearance of a fetal pole.

 

Miscarriage

If the follow-up ultrasound shows no development from the previous ultrasound, the doctor can conclusively diagnose miscarriage. In these circumstances, an empty gestational sac or a blighted ovum may be used to describe the failed pregnancy. This means that the gestational sac forms but the baby never develops enough to become visible on ultrasound.

In some cases, the empty gestational sac can remain intact for a number of weeks before miscarriage symptoms appear, and it may even continue to grow.

In a few cases, a miscarriage may be diagnosed by a single ultrasound that shows no fetal pole.

One example is if a gestational sac is seen on the ultrasound that is larger than 25mm (with no fetal pole). 

A Word From Verywell

If you have any questions or worries or questions about how your baby is developing, please speak with your doctor. How a baby develops is a complex process, so it is natural to be curious or even have some anxiety.

Sources:

American College of Obstetrics and Gynecology. (May 2015). Practice Bulletin: Early Pregnancy Loss.

American Pregnancy Association, (August 2015). Concerns Regarding Early Fetal Development.

Doubilet, P.M. et al. (2013). Diagnostic criteria for nonviable pregnancy early in the first trimester. N Engl J Med, Oct, 369, 15, 1443-51.

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