The Hegar sign is a physical finding historically used by clinicians to suggest the presence of an early pregnancy. It is one of the probable signs of gestation, meaning it is an objective change a healthcare provider can observe during a physical examination, though it does not provide definitive confirmation of a pregnancy. This sign involves a noticeable alteration in the consistency of the lower part of the uterus and is detected via a bimanual pelvic examination performed by a skilled clinician.
Defining the Hegar Sign
The Hegar sign is characterized by the softening and increased compressibility of the uterine isthmus, the narrow segment of the uterus located between the main body (fundus) and the cervix. During a bimanual examination, the clinician places two fingers into the vagina and applies pressure on the lower abdomen with the other hand, allowing them to palpate the uterus.
The softening of the isthmus is so pronounced that the fingers of the examining hands can almost meet through the tissue. This creates the sensation that the firm cervix and the main, enlarging uterine body are two separate structures. The lower uterine segment yields easily to gentle pressure, distinguishing it from the firmer tissues above and below it. The sign was named after German gynecologist Ernst Ludwig Alfred Hegar, who described it in the late 19th century.
The Anatomical Basis
The physical softening that defines the Hegar sign results from physiological adaptations to early pregnancy, primarily a dramatic increase in vascularity and the influence of hormones on uterine muscle fibers. Elevated levels of hormones, particularly progesterone and estrogen, cause the smooth muscle and connective tissues in the isthmus to relax and become pliable.
This hormonal effect is coupled with hyperemia, a massive increase in blood flow and congestion to the pelvic organs. The combination of tissue relaxation and increased fluid content makes the uterine isthmus highly compressible. While the isthmus softens, the fundus (the upper part of the uterus) simultaneously begins to enlarge and firm up to accommodate the developing conceptus.
The distinct contrast between the soft, compressible isthmus and the firmer, enlarging fundus above it makes the sign noticeable to the examiner. Below the isthmus, the cervix also undergoes some softening (known as Goodell’s sign) but remains comparatively rigid. This difference in consistency—the soft isthmus sandwiched between the firm fundus and the less yielding cervix—is the physical manifestation of the Hegar sign.
Timing and Clinical Use
The Hegar sign typically becomes detectable between the sixth and twelfth weeks of gestation. It is generally easier to appreciate the change during the second half of the first trimester, with its peak prominence around the eighth to tenth week. As the pregnancy progresses beyond the twelfth week and the entire uterus begins to enlarge and ascend out of the pelvis, the ability to palpate the isthmus distinctly decreases.
Despite its historical importance, the Hegar sign is classified only as a probable sign of pregnancy, meaning it is suggestive but not conclusive. Similar softening can occur in non-pregnant individuals due to conditions like pelvic congestion. Furthermore, the sign’s detection is subjective and depends heavily on the skill of the examiner and the patient’s body habitus.
In modern clinical practice, the Hegar sign has largely been superseded by more accurate and less invasive diagnostic methods. Reliable confirmation of pregnancy now relies on the detection of human chorionic gonadotropin (hCG) in blood or urine or direct visualization of the gestational sac or fetus via ultrasound. However, the Hegar sign still serves as a teaching tool to illustrate the profound physical changes that occur in the reproductive tract in early pregnancy.