Chew P C, Mok H, Ratnam S S
Br J Obstet Gynaecol. 1976 Nov;83(11):861-3. doi: 10.1111/j.1471-0528.1976.tb00761.x.
Plasma unconjugated oestradiol-17 beta, total oestriol and human placental lactogen levels were measured in twelve healthy volunteers admitted for bed rest in the last trimester of pregnancy. No significant alteration in levels was observed.