Sudden shifts between feeling intensely hot and developing unexpected chills or cold sweats are common during pregnancy. These temperature fluctuations, often described as hot flashes or night sweats, affect a large percentage of expectant individuals. These dramatic swings are a normal physiological response resulting from the complex biological processes required to support a growing fetus.
The Physiological Drivers of Heat Generation
The body’s baseline metabolic rate increases significantly during pregnancy. Supporting the demands of a developing fetus and the placenta requires greater energy expenditure, which elevates the body’s baseline temperature. This sustained increase in energy conversion makes the pregnant person feel warmer even at rest.
A major change contributing to the heat sensation is the dramatic increase in circulating blood volume, which expands by up to 50% by the third trimester. This extra volume supplies nutrients and oxygen to the uterus and placenta. The heart must work harder to handle this increased volume, naturally generating more heat as a byproduct of its increased effort.
To prevent overheating, the body dissipates excess heat through vasodilation. Blood vessels near the skin surface widen, moving warm blood closer to the air for cooling. This increased blood flow causes the flushed appearance and the sensation of being hot, as the body works constantly to shed the extra heat generated by increased metabolism and blood volume.
Hormones and the Body’s Thermostat
The hypothalamus, the body’s temperature regulation center, is directly affected by the cascade of pregnancy hormones. This gland in the brain acts as the internal thermostat, setting the desired temperature set point. Hormonal signals constantly adjust this set point, creating the sensation of hot and cold.
Progesterone, which rises steadily throughout pregnancy, has a thermogenic effect. This hormone raises the basal body temperature by subtly increasing the hypothalamic set point. This persistent elevation makes the body feel warmer overall, similar to the minor temperature increase experienced during the menstrual cycle’s luteal phase.
Rapid fluctuations in estrogen and progesterone levels can confuse the hypothalamus. When the set point is suddenly adjusted downward, the body attempts to rapidly cool itself through sweating, leading to a hot flash. Conversely, if the set point is suddenly raised, the body reacts by feeling cold and triggering chills as it tries to generate heat to meet the new temperature.
These hormonal shifts, distinct from the physical generation of heat, directly impact the perception of temperature. The body constantly tries to recalibrate its internal temperature against a moving hormonal target. This continuous adjustment is the primary driver behind the sudden swings between feeling overheated and chilled.
Practical Strategies for Temperature Regulation
Managing rapid temperature shifts is best achieved through strategic layering of clothing. Wearing multiple thin layers allows for quick removal or addition based on the current sensation. Choosing natural, breathable fabrics like cotton or linen helps wick moisture away when sweating occurs, preventing a subsequent chill.
Maintaining adequate hydration is an effective strategy for regulating body temperature. Sweat is the body’s primary cooling mechanism, and without sufficient water intake, this process becomes inefficient. Drinking plenty of water helps maintain the necessary fluid volume for sweating and prevents overheating.
Controlling the immediate environment, particularly during sleep, can significantly reduce night sweats. Keeping the bedroom temperature slightly cooler than usual, ideally between 60 and 68 degrees Fahrenheit, is recommended. Using a small bedside fan can also provide targeted cooling during a hot flash.
When the sensation of cold strikes, add warmth gently rather than rapidly overheating. Wearing socks or using a light, breathable blanket provides comfort without triggering a subsequent sweat response. Avoid sitting directly next to high-powered heaters, which can cause an immediate swing back to being hot.
Carrying a small, reusable cool pack or a spray bottle filled with water provides immediate relief during daytime hot flashes. Applying a cool compress to pulse points like the wrists or neck helps cool the blood flowing to the rest of the body. These portable tools empower the individual to take immediate action when a temperature swing occurs.
When Temperature Fluctuations Signal a Problem
While feeling warm is normal, an actual fever is not a typical symptom of pregnancy and requires immediate medical attention. A temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher often indicates an underlying infection, such as a urinary tract infection or a viral illness. Contacting a healthcare provider is necessary to determine the cause and treatment plan.
Severe, uncontrollable shivering or chills accompanied by other symptoms should prompt a call to the doctor. This includes symptoms like intense headache, abdominal pain, or changes in fetal movement. These combinations can signal a serious systemic issue that needs investigation beyond simple hormonal fluctuations.
Excessive sweating, particularly at night, can lead to dehydration if fluids are not adequately replenished. Signs of severe dehydration, such as dark-colored urine, profound dizziness, or a rapid heart rate, require immediate medical assessment. While temperature fluctuations are normal, a sustained inability to regulate fluid balance is a cause for concern.