Identification of pregnancy from bloodstains by radioimmunoassay for pregnancy specific β₁-glycoprotein (SP₁)

Pregnancy specific β₁-glycoprotein (SP₁), one of the pregnancy-specific proteins, has been detected by a radioimmunoassay, and its usefulness for the identification of pregnancy blood and bloodstains has been investigated. The lowest measurable concentration of SP₁, obtained by a radioimmunoassay, was found to be about 4 ng/ml. SP₁ was detected in pregnancy blood samples as early as the 5th week of pregnancy at a level of 0.945 μg/ml, and it reached on average 95.83 μg/ml in the 10th month after gradual increases. In testings of pregnancy bloodstain SP₁ was 0.883 μg/ml at the 5th week of pregnancy, then gradually increased, and became 89.94 μg/ml on average in the 10th month of pregnancy. In blood or in bloodstain samples from subjects other than pregnant women, the umbilical cord blood of newborn babies had 0.08 μg/ml (mean) of SP₁, and their umbilical cord bloodstains also contained trace amounts of SP₁, while no SP₁ was detected in blood or in the bloodstain samples from nonpregnant women, men and infants. SP₁ in pregnant blood samples stored at room temperature remained stable for 2 weeks, but then it decreased relatively rapidly to 43.0% in 1 month, 7.1% in 2 months, and 2.6% in 3 months, of the original amount. In bloodstain samples stored at room temperature, SP₁ remained relatively stable, and 55.0% of the pre-staining level was detected 6 months later, 47.5% after 1 year, and 27.0% 2 years later. SP₁ in pregnant blood was relatively unstable to heat. Heating at 50°C for 30 min decreased SP₁ to 59.8%, and at 60° for 30 min it decreased further to 1.2%. In pregnant bloodstains, SP₁ proved fairly stable to heating for 30 min in a temperature range from 50°C to 120°C, and 74.6% remained even after heating at 150°C for 30 min. Identification of pregnancy bloodstains was attempted using our standard procedures and experimentally prepared bloodstains (5 mm in diameter) on cotton cloth stored at room temperature. As a result, SP₁ was detected in all 201 pregnancy bloodstains tested, which had been prepared with blood samples collected from 2-10 month pregnant women and stored for 1 day-2 years, and the positivity was 100%. On the other hand, all bloodstains that had been prepared with blood samples from non-pregnant subjects showed negative results. Thus, pregnant bloodstains were distinguishable from non-pregnant bloodstains. These results indicate that the present method utilizing radioimmunoassay for SP₁ is a highly specific and sensitive method for identifying pregnancy blood.