<P> Ultrasound is also a common tool for determining viability . A lower than expected heart rate or missed development milestones may indicate a problem with the pregnancy . Diagnosis should not be made from a single ultrasound, however . Inaccurate estimations of fetal age and inaccuracies inherent in ultrasonic examination may cause a scan to be interpreted negatively . If results from the first ultrasound scan indicate a problem, repeating the scan 7--10 days later is reasonable practice . </P> <P> Records of attempts at pregnancy testing have been found as far back as the ancient Greek and ancient Egyptian cultures . The ancient Egyptians watered bags of wheat and barley with the urine of a possibly pregnant woman . Germination indicated pregnancy . The type of grain that sprouted was taken as an indicator of the fetus's sex . Hippocrates suggested that a woman who had missed her period should drink a solution of honey in water at bedtime: resulting abdominal distention and cramps would indicate the presence of a pregnancy . Avicenna and many physicians after him in the Middle Ages performed uroscopy, a nonscientific method to evaluate urine . </P> <P> Selmar Aschheim and Bernhard Zondek introduced testing based on the presence of human chorionic gonadotropin (hCG) in 1928 . Early studies of hCG had concluded that it was produced by the pituitary gland . In the 1930s, Georgeanna Jones discovered that hCG was produced not by the pituitary gland, but by the placenta . This discovery was important in relying on hCG as an early marker of pregnancy . In the Aschheim and Zondek test, an infantile female mouse was injected subcutaneously with urine of the person to be tested, and the mouse later was killed and dissected . Presence of ovulation indicated that the urine contained hCG and meant that the person was pregnant . A similar test was developed using immature rabbits . Here, too, killing the animal to check her ovaries was necessary . An improvement arrived with the frog test, introduced by Lancelot Hogben, which still was used in the 1950s and allowed the frog to remain alive and be used repeatedly: a female frog was injected with serum or urine of the patient; if the frog produced eggs within the next 24 hours, the test was positive . This was called the Bufo test, named after the toad genus Bufo, which was originally used for the test . Other species of toads and frogs have been used later on . </P> <P> Hormonal pregnancy tests such as Primodos and Duogynon were used in the 1960s and 1970s in the UK and Germany . These tests involved taking a dosed amount of hormones, and observing the response a few days later . A pregnant woman does not react, as she is producing the hormones in pregnancy; a woman not pregnant responds to the absence of the hormone by beginning a new menstrual cycle . While the test was (is) generally considered accurate, research advancements have replaced it with simpler techniques . </P>

When does beta hcg become positive in urine