What position should women in their second or third trimester of pregnancy avoid when performing exercise?

The prone position is impractical later in pregnancy due to the growing abdomen but does not carry the specific vascular compression risk that makes supine the primary contraindicated position in these trimesters.

In the supine position, the gravid uterus compresses the inferior vena cava, impairing venous return to the heart and potentially causing supine hypotensive syndrome, which reduces uteroplacental blood flow. This risk increases substantially in the second and third trimesters as uterine size grows. Major obstetric guidelines, including those from ACOG, specifically recommend avoiding the supine position during exercise after the first trimester.

The lateral or side-lying position is actually recommended and considered safe for pregnant women because it avoids compressing the inferior vena cava.

The hands-and-knees position is generally considered safe during pregnancy and does not produce the hemodynamic compromise associated with the supine position.