Influence of ritodrine on plasma steroids and human placental lactogen levels in third-trimester pregnancies.

The effects of ritodrine, administered by intravenous, intramuscular or per os routes, upon plasma levels of unconjugated estriol, estradiol, progesterone and human placental lactogen (HPL) were investigated in 24 third-trimester pregnancies. Ritodrine administered at a constant rate of 200 micrograms/min for 3 h, injected intramuscularly 8 x 10 mg/day for 5 days or given orally in doses of 6 x 20 mg/day for 10 days resulted in a significant decrease in the steroid hormone concentration and a significant elevation of HPL levels.