Supine Hypotensive Syndrome is caused by which mechanism?

• A. Lightening
• B. Compression of vena cava by uterus
• C. Fetal head visible at vaginal opening
• D. Area between vagina and anus

Answer: (B)

Supine hypotensive syndrome happens when a pregnant person lies on the back and the enlarged uterus presses on the inferior vena cava as it runs behind the abdominal organs. This compression reduces venous return to the heart (lower preload), which drops cardiac output and can lead to maternal hypotension. With less blood flowing through the placenta, fetal perfusion can also decline, potentially causing fetal distress. The left lateral position relieves the pressure of the uterus on the IVC, restoring venous return and stabilizing both mother and fetus.

Lightening is the fetus descending into the pelvis late in pregnancy and is not the mechanism here. The fetal head visible at the vaginal opening is a sign of active labor, not the vascular compression causing this syndrome. The area between the vagina and anus is simply the perineum and has no role in this mechanism.