Feeling suddenly overheated or experiencing a wave of warmth over the face, neck, and chest is a common sensation in the final weeks of pregnancy. This symptom, often referred to as a hot flash, can be noticeable and disruptive, especially at night. For those nearing their due date, every physical change brings a question: Is this a sign that labor is about to begin?
Are Hot Flashes a Reliable Indicator of Labor?
A feeling of intense, sudden warmth is generally not considered a reliable or primary indicator that true labor is imminent. While some report hot flashes or chills during the early phase of labor, the symptom itself is not a predictive sign that contractions are actively starting. Hot flashes are a well-documented physical experience throughout the third trimester, often occurring weeks before delivery. It is more accurate to view these episodes as a persistent side effect of late-stage pregnancy rather than a direct signal that the body is shifting into labor.
Physiological Reasons for Increased Body Heat During Pregnancy
The underlying cause of feeling warmer during the final weeks of pregnancy is a combination of dramatic internal physiological changes. Progesterone, a hormone that remains at high levels throughout gestation, has a thermogenic effect, meaning it directly acts to raise the body’s core temperature slightly. The body also experiences a significant increase in its metabolic rate to support the growth and energy demands of the developing fetus. This faster metabolism naturally produces more heat as a byproduct.
Another element is the total volume of blood circulating in the body, which increases by up to 50% by the third trimester. This greater blood volume requires the heart to pump more frequently, and the blood vessels near the skin surface widen (vasodilation) to help dissipate the excess heat. The growing fetus itself also generates its own body heat, which the maternal system must absorb and regulate.
Established Physical Signs That Labor is Starting
If hot flashes are not a definitive signal, attention should be directed toward the established physical changes that indicate labor is beginning. The most reliable sign of true labor is the presence of uterine contractions that become progressively longer, stronger, and closer together. Unlike practice contractions, these contractions do not ease up with a change in position or activity and require attention to breathe through them.
Another unmistakable sign is the rupture of membranes, commonly known as the water breaking, which may present as a sudden gush or a slow, steady trickle of fluid. The loss of the mucus plug, sometimes accompanied by a small amount of blood and referred to as the “bloody show,” also suggests that the cervix is beginning to soften and open. While the mucus plug can be lost days or even weeks before labor begins, its presence indicates cervical preparation.