What is Fetal Pole?- When is it Developed?


Pregnancy period lasts for 38 to 40 weeks, counted from the last menstruation. Pregnancies can be detected easily by blood and urine tests. The first physical sign of a foetus will appear in the form of a structure known as the fetal pole. During this point, the embryo is barely visible as a tiny comma shaped structure. Sometimes, the fetal pole might not be visible via ultrasound technique, but there is no need to get nervous.

A fetal pole is seen during pregnancy which is a thickening on the margin of the yolk sac of a foetus. It is usually seen at six weeks with ultrasound technique. However, it is absolutely normal for the fetal pole to not be visible until about 9 weeks.

fetal pole

In This Article:

All You Need to Know About Fetal Pole

What is a Foetal Pole?

The foetal pole will appear in the fifth week of pregnancy as a 3-5 mm thickening around the margin of the foetal yolk sac, which helps in providing nutrition for the growing embryo. This will continue to grow at the rate of one mm per day, making its length a handy approximation for the age of the foetus. The age is measured by adding the length of the foetus in mm to 6 weeks. For example, if the foetal pole is six mm long, then its age is six weeks and six days.


When is it Seen on Ultrasound?

Around the second month of pregnancy, the doctor might suggest a trans abdominal or trans vaginal ultasonography technique. This technique helps in identification of developmental changes in the foetus such as the formation of the foetal pole and detection of the foetal heartbeat.

Missing Foetal Pole: Is it a Concern?

Sometimes the foetal pole is not seen on an ultrasound, why this is so? If there is no foetal pole seen at 6 weeks, it need not mean the worst and not to worry. There are several factors involved in the detection of a healthy foetus like the size of the gestational sac, menstrual cycle, measurement error and so on.

  • The pregnancy has been dated incorrectly – the timescale for the appearance of the foetal pole can range between six and nine weeks, predicting the time of conception incorrectly by even a few days could create an inaccurate reading of the ultrasound. For example, misremembering the last menstrual period could throw off the predicted dates. Also, irregular cycles which are not consistently followed by ovulation two weeks after the period could mean that the pregnancy is not old.
  • The pregnancy has failed – unfortunately, the absence of a foetal pole can often mean that the pregnancy has not worked or that a miscarriage has happened. In some extreme cases, the uterine sac can develop and grow further for weeks before miscarriage can be identified. Another possibility of miscarriage is the presence of a gestational sc larger than twenty five mm without the foetal pole.

What if there is a Foetal Pole but no Heartbeat?

When the foetus is around seven weeks old, its heartbeat is detectable. Normal range of heart rate will be 100-110 beats per minute. However, if the heartbeat is lower than 90 bpm, then it could be a non-viable pregnancy. Also, if the foetal pole can be seen, but the heartbeat is absent, all indications lead to miscarriage or an ectopic pregnancy.


The doctor will suggest for a follow up ultrasound in the next coupleof weeks to give the pregnancy enough time to develop. Only if the future scans show similar result the doctor wwill confrim that a miscarriage has occured. The procedure of development of a baby is a very complex process.  The mother should make sure for a healthy baby.


Foetal pole is considered the first direct imaging manifestation of the foetus and is seen as a thickening on the margin of the yolk sac during early pregnancy. It is identifies at 6 weeks by ultrasound. When the foetal pole is less than or equal to 7, a foetal heartbeat is detected.


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