Hegar's Sign: An Early Sign of Pregnancy Explained

Hegar's sign is a term often encountered in obstetrics and nursing education, referring to one of the earliest physical indicators of pregnancy. While the advent of modern pregnancy tests has made it less critical for diagnosis, understanding Hegar's sign offers valuable insight into the physiological changes that occur during early gestation. This article provides a comprehensive look at its definition, detection, underlying causes, and its relevance in modern medicine.

What is Hegar's Sign?

Hegar's sign is a non-sensitive, probable sign of pregnancy characterized by the distinct softening and compressibility of the lower uterine segment, also known as the uterine isthmus. The isthmus is the anatomical region that connects the firm cervix to the main muscular body of the uterus.

This sign is typically detectable by a trained healthcare provider during a bimanual pelvic exam between the 4th and 12th week of pregnancy. The softening is so pronounced that on examination, the cervix and the body of the uterus may feel like two separate regions.

The Historical Context: From Key Indicator to Outdated Sign

The sign is named after Dr. Ernst Ludwig Alfred Hegar, a German gynecologist who described it in 1895. Before the development of reliable hormonal assays (like urine and blood tests for hCG) and ultrasound technology, clinicians depended on a collection of physical signs to diagnose pregnancy. Hegar's sign, along with others like Goodell's sign and Chadwick's sign, was a cornerstone of early obstetric assessment.

While Dr. Hegar is credited with popularizing the sign, historical records indicate that one of his assistants, Reinl, first described it in 1884. Today, its diagnostic role has been largely superseded by more accurate methods.

How is Hegar's Sign Detected? The Bimanual Examination

Detecting Hegar's sign requires a gentle bimanual pelvic examination performed by a skilled healthcare professional, such as a doctor, nurse practitioner, or midwife.

The procedure involves:

1. The examiner inserts two gloved fingers into the vagina to palpate the cervix and the anterior fornix (the space in front of the cervix).
2. The other hand is placed on the lower abdomen, just above the pubic bone, to press down on the uterine fundus (the top of the uterus).
3. The examiner then attempts to compress the lower uterine segment between the internal and external fingers.

If Hegar's sign is present, the softened isthmus will be easily compressible, creating the sensation that the fingers can almost meet. This must be done with extreme care to avoid disrupting a potential early pregnancy.

!Diagram illustrating the bimanual pelvic examination to detect Hegar's sign

A depiction of the bimanual examination technique used to assess pelvic organs. Source: Wikimedia Commons

Understanding the Pathophysiology: What Causes Hegar's Sign?

The softening observed in Hegar's sign is not random; it's a result of complex physiological changes driven by the hormones of early pregnancy.

Hormonal and Vascular Changes

The surge in hormones—primarily estrogen, progesterone, and human chorionic gonadotropin (hCG)—dramatically increases blood flow (hyperemia) to the pelvic organs. This engorgement and increased vascularity contribute significantly to the softening of the uterine tissues.

Connective Tissue Remodeling

The most profound changes occur within the connective tissue of the uterine isthmus. Research shows that during pregnancy:

• Collagen Concentration Decreases: The concentration of collagen, the primary structural protein, is nearly halved. The collagen fibers themselves become thinner and more dispersed.
• Proteoglycan Composition Shifts: Changes in the molecules surrounding the collagen fibers (proteoglycans) make the collagen more extractable and flexible.

This fundamental remodeling prepares the uterus for the rapid growth required to accommodate the developing fetus.

Hegar's Sign vs. Other Probable Signs of Pregnancy

Hegar's sign is part of a classic triad of "probable" signs of pregnancy. It's important to distinguish it from the others:

Sign	Description	Location
Hegar's Sign	Softening and compressibility	Lower Uterine Segment (Isthmus)
Goodell's Sign	Softening of the cervical tip	Vaginal portion of the cervix
Chadwick's Sign	Bluish-purple discoloration	Cervix, vagina, and vulva

!A simple chart comparing the locations of Hegar's, Goodell's, and Chadwick's signs on a diagram of the uterus.

Comparison of early pregnancy signs. Source: Osmosis.org

Diagnostic Accuracy and Limitations

It is crucial to understand that Hegar's sign is a probable, not a positive, sign of pregnancy. This means it strongly suggests pregnancy but does not definitively confirm it.

Why It's Not Definitive

• Non-Specific: The sign can be absent in some pregnant individuals or present in those who are not pregnant.
• Subjective: Its detection depends on the skill and experience of the examiner.
• Less Reliable in Multiparous Women: In women who have had multiple pregnancies, the uterine tissues may be permanently softer, making the sign harder to recognize.

Common Causes of a False Positive

Several conditions unrelated to pregnancy can cause softening of the lower uterine segment, mimicking Hegar's sign:

• Uterine fibroids
• Ovarian cysts
• Cervical insufficiency (weak cervical tissue)
• Inflammatory conditions like cervicitis
• Certain congenital connective tissue disorders

Contemporary Relevance: Is Hegar's Sign Still Useful Today?

In modern, well-resourced medical settings, Hegar's sign is considered largely obsolete for pregnancy diagnosis. A simple urine or blood test for hCG is far more accurate, sensitive, and objective.

However, the sign retains contextual importance:

• In low-resource settings: Where access to laboratory tests or ultrasound is limited, physical examination skills remain vital. Recognizing Hegar's sign can be a key step in identifying pregnancy and initiating timely prenatal care.
• As part of a holistic assessment: Even with modern technology, a physical exam remains a part of comprehensive prenatal care. A clinician may note Hegar's sign during a routine exam, adding another piece of information to the overall clinical picture.

Frequently Asked Questions (FAQ)

What is Hegar's sign? Hegar's sign is a probable, but not definitive, clinical sign of early pregnancy. It is characterized by the softening and compressibility of the lower segment of the uterus (the uterine isthmus), which can be detected by a healthcare provider during a bimanual pelvic examination.

When does Hegar's sign appear during pregnancy? Hegar's sign typically appears in the early stages of pregnancy, usually between the 4th and 12th week of gestation. It is most noticeable around the 6th to 8th week.

What is the difference between Hegar's sign and Goodell's sign? Both are probable signs of pregnancy but affect different areas. Hegar's sign is the softening of the lower uterine segment (the isthmus) that connects the cervix to the main body of the uterus. Goodell's sign is the softening of the vaginal portion of the cervix itself.

Is Hegar's sign a definitive proof of pregnancy? No, Hegar's sign is not a definitive proof of pregnancy. It is considered a 'probable' sign because it can be absent in some pregnant women and present in non-pregnant women due to other conditions. Definitive signs of pregnancy include detecting a fetal heartbeat, visualizing the fetus via ultrasound, and a positive hCG test.

References

• Cunningham, G. (2010). Williams Obstetrics (23rd ed.). McGraw-Hill Medical.
• Dutta, D.C. (2013). Textbook of Obstetrics. New Central Book Agency Ltd.
• Medical News Today. (2023). Hegar's sign: What is it and what does it mean?. Retrieved from https://www.medicalnewstoday.com/articles/hegars-sign
• Osmosis.org. Hegar Sign: What Is It, Causes, and More. Retrieved from https://www.osmosis.org/answers/hegar-sign
• Wikipedia. (n.d.). Hegar's sign. Retrieved from https://en.wikipedia.org/wiki/Hegar%27s_sign