The involuntary shivering, trembling, or teeth-chattering experienced during active labor or immediately following delivery is known as the “labor shakes.” This intense, uncontrollable shaking can be startling for birthing people and their support partners, but it is a common physical response to childbirth. Estimates suggest that between 40% and 75% of birthing people experience these tremors at some point in the process. The shakes are almost always a normal, temporary physiological reaction, indicating the body is navigating the profound physical and chemical shifts of labor.
The Hormonal Rush: Adrenaline and Stress Response
One of the most significant contributors to the labor shakes is the influx of chemical messengers within the body. The intense physical experience of contractions and the general stress of labor trigger a “fight-or-flight” response in the nervous system. This activation leads to a surge of catecholamines, specifically epinephrine (adrenaline) and norepinephrine, which are powerful stress hormones.
As these hormones flood the system, they cause a host of physical reactions, including a rapid heart rate, heightened alertness, and increased muscle tension. Adrenaline, in particular, can stimulate involuntary muscle activity, which manifests as the visible shaking or trembling. Cortisol, another stress hormone, also rises during this period, further contributing to the body’s over-alert state and physical agitation.
This hormonal cascade is a natural mechanism that occurs as the body nears the peak of its work. The sudden, intense presence of these chemicals can overwhelm the system, causing the muscles to activate in a way that feels similar to a full-body tremor. This shaking is a direct reflection of the intensity of the signals being transmitted through the nervous system during this physically demanding period.
Temperature Shifts and Epidural Impact
The body’s system for maintaining a stable internal temperature, known as thermoregulation, is frequently disrupted during labor, leading to shivering. Shivering is the body’s primary mechanism for generating heat through rapid, involuntary muscle contractions when it senses a drop in core temperature. Labor itself can cause core temperature fluctuations, which may trigger a natural attempt to warm up.
The use of regional anesthesia, such as an epidural, complicates this temperature regulation. The anesthetic medication blocks nerve signals, causing the blood vessels in the lower body to relax and widen, a process called vasodilation. This widening allows warm blood from the core to flow into the legs and pool there, diverting heat away from the body’s center.
This shift can confuse the hypothalamus, which acts as the body’s thermostat, causing it to incorrectly register a drop in core temperature. In response, the hypothalamus triggers an intense, involuntary shivering response in an attempt to rapidly generate heat and compensate for the perceived cold. Receiving large volumes of un-warmed intravenous fluids, which is common during labor, can also contribute to a drop in temperature, further intensifying the shivering response.
Metabolic Demand and Muscular Exhaustion
Beyond hormonal surges and temperature shifts, the physical exertion of labor itself contributes to the development of muscle tremors. Labor is an intense, sustained muscular effort that can be compared to running a marathon, demanding significant energy from the body. Contractions require the continuous, repeated work of the uterine muscles, which affects the entire muscular system.
This prolonged physical output can lead to the depletion of glycogen, the stored form of glucose that fuels muscle activity. As energy stores are used up, the muscles become fatigued and may begin to tremble from exhaustion. Furthermore, intense muscular work leads to the buildup of metabolic byproducts, such as lactic acid, within the muscle tissue. The combination of muscle fatigue, energy depletion, and chemical changes in the muscle environment can cause involuntary muscle spasms and shaking.
What To Do When the Shakes Start
When the labor shakes begin, recognize that they are a normal, temporary response and not a sign of complication in most cases. Focused breathing techniques and attempts to relax the jaw and shoulders can sometimes help mitigate the intensity of the tremors. Since temperature changes are a common cause, applying comfort measures can provide relief.
The nursing staff can often assist with temperature regulation:
- Providing warm blankets.
- Using forced-air warming devices to apply heat to the upper body, which can counteract the chilling sensation.
- Warming intravenous fluids before they are administered to help prevent further drops in core temperature.
- Communicating with the medical team, as they can offer reassurance and monitor the situation.
While shaking is usually benign, it is important to notify the care team if the tremors are accompanied by other symptoms, such as a fever above 38°C (100.4°F), a severe headache, or confusion. These symptoms are rare but could suggest an underlying issue like an infection, which warrants immediate medical attention. In the vast majority of cases, the shakes subside naturally shortly after delivery as hormones rebalance and the body recovers.