Markers of type I and type III collagen synthesis in serum as indicators of tissue growth during pregnancy.

The concentrations of the carboxy-terminal propeptide of type I procollagen (PICP) and the amino-terminal propeptide of type III procollagen (PIIINP) in serum were followed prospectively as indicators of synthesis of the respective collagens in 266 healthy primiparas during the second and third trimesters of pregnancy. The PIIINP concentration increased 2-fold during the third trimester; the median value was 10.0 micrograms/L at gestational week 40, with a range from 4.6-32.7 micrograms/L (reference interval for nonpregnant women, 1.7-4.2 micrograms/L). A significant increase also took place in the PICP concentration. The frequency distributions of the two parameters were near normal at week 26. They started to broaden out at week 32 and were wide at week 38. In severe preeclampsia, PIIINP tended to increase more than in normal pregnancies of the same duration. The increase in PIIINP correlated significantly with maternal weight gain and the birth weight of the infant, but not with other parameters related to pregnancy or delivery. At gestational week 38, there was a significant correlation between the circulating concentrations of insulin-like growth factor-I and PIIINP or PICP, but not between human placental lactogen and PICP, and only a weak association between human placental lactogen and PIIINP. This suggests that insulin-like growth factor-I is involved in the regulation of type I and type III collagen synthesis during pregnancy.