Serveral different types of collagen have been identified invivo. Human
   placenta has been employed by a number of investigators over the past
   decade as a starting material for isolation and characterization of different
   genetic types of collagen including type I,III,IV and IV molecules.

          Proteases of the placenta participate in the degradation of intracellular
   and extracelluar matrix proteins. To extract collagen types IV and I+III , a
   healthy placenta at term (38 weeks) and a premature placenta (14 weeks)
   were placed under pepsin digestion using minimum quantity. The steps of
   extraction were controlled by the SDS-PAGE.

          The electrophoretical patterns of premature placental collagen
   indicated that the number of collagen chains types IV and I+III in premature
   placenta were less than that of the healthy placenta at term.  According
   to electrophoretical pattern in the premature placenta , there were not
   a2(IV) , b11(I) , b12(I) and a1(III) chains. Thus , it is probable that in some of the
   repeating abortion the synthesis of collagen is decreased or degradation of
   collagen is increased.

          So it is suggested to measure the serum and cervix collagenase in
   women who had unexplained abortions.