Signs of Heartbeat in the Fetal Pole

A normal pregnancy is counted as 40 weeks, and is counted from day one of the last menstrual period. At the time of a missed period, a woman is considered to be four weeks pregnant. Early signs of pregnancy can only be detected by blood tests or by ultrasound. Around six weeks, the fetal pole, which is the first part of the human embryo to develop, is seen on ultrasound. A heartbeat in the fetal pole is first seen around six to six and a half weeks.

Appearance of Fetal Pole

The fetal pole has no arm or leg buds yet and looks like a curved pole or a bent shrimp, with what will be the embryo’s head at one end and a tail at the other end. According to the Military Obstetrics and Gynecology, the fetal pole grows about 1 mm per day after it appears at 6 weeks of pregnancy. The fetal pole is measured by crown-rump (CRL) length, which measures not from end to end but from the top to the “bend” in the embryo.

A fetal heartbeat can be detected on ultrasound around 6 weeks, or when the CRL length reaches around 5 mm, which occurs between 5 1/2 to 6 1/2 weeks, according to the American Pregnancy Association.

Fetal Heartbeat

When a baby is born, the fetal heartbeat is between 120-160 beats per minute (BPM), but when the heart first starts to beat, it beats only 90 to 110 times per minute. According to Military Obstetrics and Gynecology, the rate is less important than the presence or lack of fetal heartbeat, although a heart rate of less than 90 BPM with a CRL of 5 mm may mean the pregnancy is not viable, according to Obstetric Ultrasound written by Dr. Joseph Woo.

Implications

If a woman thinks she got pregnant earlier than she actually did, the lack of a fetal heartbeat by 6 1/2 weeks of pregnancy may be alarming. But if the fetal pole hasn’t reached a CRL of 5 mm, the pregnancy may not be as advanced as thought. A fetal pole with a heartbeat indicates a 70 to 90 percent chance that the pregnancy will be viable and result in a live birth, according to the American Pregnancy Association. Conversely, a lack of fetal heartbeat by the time the fetal pole reaches 5 mm is an ominous sign and indicates possible miscarriage or blighted ovum, a pregnancy in which placental tissue grows but no embryo develops.

About this Author

Sharon Perkins has worked as a registered nurse in oncology, labor/delivery, neonatal intensive care, infertility, and ophthalmology. Perkins started writing professionally for the Wiley “Dummies” series in 2001, and has co-authored 7 books for the series, and acted as developmental editor for several more. Perkins received her Registered Nursing degree from Western Oklahoma State College in 1986.