Fatigue in the third trimester

By trimester

Weeks 28–birth

3rd trimester

Fatigue this late usually comes from a few things together: disrupted sleep from nighttime bathroom trips, reflux, and trouble getting comfortable, plus rising iron needs and the physical load of carrying a full-size baby. Providers often recheck iron levels and thyroid function around now. Sleeping on your left side with a pillow for support can meaningfully improve your sleep.

What does the evidence show for fatigue in the third trimester?

• Sleep disturbances are common in the third trimester and can make daytime fatigue worse, driven by nighttime bathroom trips, reflux, back pain, and trouble getting comfortable. 1
• Side sleeping, especially on the left, is generally recommended by the second and third trimesters for better blood flow and comfort. 2
• Iron-deficiency anemia becomes more common later in pregnancy and can show up as worsening fatigue, so iron supplementation levels are best set with your provider's guidance. 3
• Continued moderate activity, with modifications as needed, is part of the standard approach to keeping energy, mood, and sleep quality up in the third trimester. 4
• Iron-deficiency anemia in pregnancy shows up as feeling tired or faint, shortness of breath, and becoming pale, and it sits on the same list of common pregnancy complications as preeclampsia and hyperemesis gravidarum. 5

When should I call my provider about fatigue in the third trimester?

Ordinary third-trimester tiredness builds slowly and eases with rest. What does not fit that shape is fatigue paired with shortness of breath, feeling faint, or noticeably pale skin, which is the iron-deficiency anemia picture and earns a blood count rather than more naps. Bring up weakness and trouble concentrating in the same conversation, since those track with low iron too. Low iron in pregnancy carries associations with premature birth and low birthweight, so this is a raise-it-now finding, not a wait-and-see one. If you are ever unsure which side of the line you are on, make the call. Obstetric teams handle these check-ins as routine, not as overreacting.