Core body temperature and the thermoneutral zone: a longitudinal study of normal human pregnancy

Using a longitudinal study design, we investigated changes in maternal core temperature and ambient temperatures before and after a localized cooling procedure to the right hand.

Fifteen pregnant women participated. The experiments were sequentially performed for 21 month periods on each subject: from the 8th week of gestation to 1 year after delivery on seven separate occasions (gestational weeks 8, 16, 26, 36 and 12, 24, 52 weeks post-partum). The experiments were conducted in a climactic chamber, allowing ambient temperature adjustment to each subjects' thermoneutral zone determined using Doppler ultrasound of the digital artery.

Maternal core temperature decreased from 37.1 °C (week 8) towards term, reaching a nadir (36.4 °C) at 12 weeks post-partum (P < 0.001). The ambient temperature required to reach the thermoneutral zone changed significantly from 26.5 °C (week 8) falling to its lowest point: 23.0 °C (week 36) (P < 0.001), then stabilized from 24 weeks post-partum.

Maternal core temperature is highest in the first trimester but falls during pregnancy to a nadir 3 months post-partum. The ambient temperature required to reach the thermoneutral zone was 4 °C lower at 36 weeks of gestation compared with early pregnancy and late post-partum. Human temperature regulation is altered in pregnancy and for at least 3 months post-partum.