Why you feel hot all the time during pregnancy

By trimester

Weeks 1–13

1st trimester

Early on, rising progesterone starts resetting your body's temperature control, so feeling warmer than usual can show up even before other pregnancy signs feel obvious, and it's easy to mistake for a low-grade illness.

Weeks 14–27

2nd trimester

By the second trimester, added blood volume is in full swing, which adds to the heat-generating side of the balance while your body's protective adaptations, like increased skin blood flow, work to keep pace.

Weeks 28–birth

3rd trimester

In the third trimester, the combined metabolic demands of your growing baby and placenta are at their highest, so feeling warm is common, but a measured fever, especially once labor begins, is a different, more serious situation specifically linked to worse outcomes for the baby, so measuring rather than guessing matters most now.

What does the evidence show for feeling hot?

• Pregnancy brings protective heat-regulating adaptations, a lower sweating threshold, increased plasma volume and skin blood flow, and greater thermal heat capacity from rising body mass, that work against heat-generating changes like increased body mass and fat, a shifting body surface-area-to-mass ratio, and metabolic heat produced by the growing fetus and placenta. 1
• Pregnant women's temperature regulation held up well under real heat exposure in the evidence reviewed: a hot bath of 40°C (about 104°F) or a dry sauna of 70°C (about 158°F) for 20 minutes kept core temperature within safe limits, and moderate exercise in heat showed no systematic change in thermoregulatory capacity. 1
• Fever during labor specifically is defined as a temperature over 38°C (100.4°F) and is associated with a number of poor fetal and neonatal outcomes, marking a clear difference between ordinary pregnancy warmth and an actual fever that needs attention. 1
• Trouble dealing with heat is listed among signs and symptoms of hyperthyroidism that can occur during pregnancy, and NIDDK notes this same symptom, along with irritability, tiredness, and a fast heartbeat, can appear during the hyperthyroid phase of postpartum thyroiditis, meaning heat intolerance is a genuine, if less common, thyroid clue as well as a normal pregnancy sensation. 2
• Outside of pregnancy, a fever in an adult is generally defined as an oral temperature above about 99°F to 99.5°F (37.2°C to 37.5°C), and almost any infection can cause one, underscoring that a measured number, not just a subjective feeling of warmth, is what defines a fever. 3
• "Fever," specifically a temperature of 100.4°F or higher, is listed among the urgent maternal warning signs that call for immediate medical attention during pregnancy and postpartum. 4

Feeling hot: normal or worth a call?

When should I call my provider about feeling hot?

A measured temperature at or above 100.4°F counts as an urgent maternal warning sign and needs prompt medical attention rather than being assumed to be ordinary pregnancy warmth. Heat intolerance alongside a racing heart, trouble sleeping, or unexplained tiredness can point toward a thyroid problem and is worth mentioning to your provider, since a blood test, not symptoms alone, is what tells a thyroid cause apart from normal pregnancy physiology. Fever specifically during labor is linked to poorer outcomes for the baby, so a measured temperature, not just how hot you feel, is what should guide whether to seek care. When in doubt, call your obstetric team the same day. Early input almost always beats waiting, and the on-call line exists exactly for this.