Feeling cold, having persistent chills, or experiencing a general intolerance to cool temperatures, can be a surprising symptom during the first trimester of pregnancy. While many people anticipate feeling warmer due to the developing pregnancy, the opposite sensation is quite common. This feeling is generally a normal physiological response to the rapid biological adjustments happening inside the body. Understanding these shifts, from temperature regulation changes to blood distribution, helps explain why this unexpected chill occurs.
Hormonal Shifts and the Body’s Thermostat
The primary driver behind early pregnancy coldness is the dramatic elevation of the hormone progesterone. Progesterone begins to surge immediately after ovulation and remains high if conception occurs, maintaining the uterine lining to support the pregnancy. This hormone has a direct action on the hypothalamus, the part of the brain responsible for regulating body temperature.
Progesterone raises the body’s thermal set point, causing a persistent elevation in basal body temperature (BBT), typically by about 0.5 to 1.0 degrees Fahrenheit. This elevation is often an early indicator of pregnancy. Even though the core temperature is higher, the body may attempt to shed this excess heat by increasing blood flow to the skin. This adjustment process can lead to a sensation of being cold or feeling a chill.
The body’s internal systems are recalibrating to operate at this new, slightly elevated temperature. This leaves a person feeling more sensitive to ambient temperature changes, which can manifest as persistent coldness or shivers.
Blood Flow Redistribution and Metabolic Rate Changes
The circulatory system undergoes profound changes to support the developing pregnancy. Total blood volume can increase by up to 50% by the end of pregnancy, and a significant portion is diverted to the growing uterus and placenta. This redistribution of blood flow prioritizes the core organs, which can draw warmth away from the peripheral areas of the body.
This shift in circulation often results in peripheral vasoconstriction, meaning the small blood vessels in the extremities constrict slightly to maintain core warmth. Consequently, many people experience cold hands and feet, even if their torso feels warm. Hormones like progesterone can also cause blood vessels to relax, leading to a slight drop in overall blood pressure (hypotension), which contributes to a general feeling of being cold or lightheaded.
Early pregnancy involves an adjustment in the basal metabolic rate (BMR), the rate at which the body uses energy at rest. As the body works harder to build new tissue and sustain the pregnancy, these energy demands shift. This can sometimes lead to temporary fluctuations in body heat production. These systemic changes compound the cold sensation initiated by hormonal shifts.
When Coldness Signals a Deeper Issue
While a mild, intermittent chill is often a normal part of early pregnancy, persistent or extreme coldness accompanied by other symptoms may signal an underlying health condition. Two common conditions that cause cold intolerance and can be diagnosed in pregnancy are anemia and thyroid dysfunction.
Anemia
Anemia, particularly iron-deficiency anemia, is common because the rapid expansion of blood volume increases the demand for iron to produce hemoglobin and red blood cells. A reduced red blood cell count impairs the blood’s ability to transport oxygen efficiently throughout the body. This impairment leads to feelings of fatigue and chronic coldness. If the coldness is paired with extreme tiredness, paleness, or shortness of breath, a blood test for iron levels is warranted.
Thyroid Dysfunction
Another cause of cold intolerance is an underactive thyroid gland, a condition known as hypothyroidism. Thyroid hormones regulate the body’s metabolism and temperature control. A deficiency can cause the symptom of feeling cold all the time. Because thyroid function is important for the early development of the baby’s brain and nervous system, any severe cold intolerance combined with symptoms like weight gain or severe fatigue should prompt a discussion with a healthcare provider for thyroid screening.