What's New in Pregnancy Tests?

Baby we've come a long way.

Traditionally diagnosis of pregnancy is based on missed menstrual periods, elevated temperature, feelings of nausea and breast changes. As the pregnancy progresses more visible signs and symptoms develop.

Pregnancy testing has evolved during the past half century from a time consuming, complicated laboratory procedure using expensive test animals into a rapid, relatively inexpensive and convenient technique.

The basis for most pregnancy tests involves the production of human chorionic gonadotropin or HCG by the placenta during pregnancy. It can be detected in blood or urine. In normal pregnancy the production of HCG begins within 48 hours after instantiation, ascends to a peak between 50 and 90 days after the last menstrual period then falls to a lower level throughout the pregnancy and finally ceases 3 - 10 days after delivery.

In 1928 two Germans, Aschheim and Zondek introduced the first biological test. They observed that urine from pregnant women injected into immature female mice caused changes in the ovaries. After repeated injections the test animals were killed 4 - 5 days later and the ovaries examined for evidence of HCG activity.

In 1932 Friedman did the same thing to rabbits and found that an earlier result could be obtained. The rabbits were killed and examined 48 hours later.

In 1941 Frank and Berman used immature female rats. These were killed and the ovaries examined 16 - 24 hours later.

In 1947, the male toad test was introduced. Injections of blood containing HCG caused the appearance of sperm in the toad's urine. The reporting time for the male load test was 1 - 5 hours and the same animals could be used again.

Since 1942 another avenue has been that of hormone tests. Either injected or taken orally, oestrogen-progestogen combinations will induce menstruation in the non-pregnant woman. Because of the suspicion of increased congenital malformation associated with the administration of these hormones during early pregnancy the use of these tests has been discouraged since 1975.

In 1960 the first immunological test carried out in a test tube became available Immunological tests utilise antibodies to detect HCG in blood or urine.

In 1962 a similar test was developed which could be done using a drop of urine on a slide. The agglutination of latex particles indicates HCG; This is the basis of the standard urine tests performed today in a doctor's surgery or laboratory. The result can be read in 2 minutes These tests however can only be carried out 10-14 days after a missed period.

The search for tests capable of detecting pregnancy at a much earlier stage continues. A new generation of tests called radioimmunoassays are capable of diagnosing pregnancy prior to or at the time of the first missed period. Instead of using latex particles this method uses HCG labelled with radioisotopes of iodine.

In 1974 a more rapid, one hour lest was developed at Cornell called a radio recept-orassay.