Thyroid function in early pregnancy II: Paradoxical growth hormone response to thyrotropin-releasing hormone

A variant of growth hormone (GH) known as human placental growth hormone (hpGH) is found in maternal serum during pregnancy. It is well established that during the second half of normal pregnancy, pituitary GH secretion is suppressed; however, there are no data about maternal GH secretion during the first trimester of pregnancy. The present study reports the response of GH to thyrotropin-releasing hormone (TRH) in eight pregnant women in the first trimester of pregnancy (weeks 6-9) who had previously requested voluntary interruption of pregnancy. The TRH test induced a significant paradoxical GH response with a peak of 9.4 ± 0.5 ng/ml (mean ± SD) at 30 min and a higher thyroid-stimulating hormone (TSH) response in pregnant women. The increment was observed until 120 min and no response was observed in the control group. These data show the paradoxical response of GH to TRH, a releasing factor to which the hormone does not normally respond. This paradoxical secretion may be due to direct pituitary stimulation and can be explained on the basis of a state of gestational hypothyroidism.