Supine hypotension syndrome is characteristic finding of the following trimester:

During third trimester, in about 10 percent of women, supine compression of the great vessels by the uterus causes significant aerial hypotension, sometimes referred to as the supine hypotensive syndrome. Also when supine, uterine aerial pressure--and thus blood flow--is significantly lower than that in the brachial aery. This may directly affect fetal hea rate patterns. This also occurs with hemorrhage or with spinal analgesia. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 5. Maternal Physiology. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.