1 00:00:06,574 --> 00:00:12,738 The earliest known pregnancy test dates back to 1350 BC in Ancient Egypt. 2 00:00:12,738 --> 00:00:14,829 According to the Egyptians, 3 00:00:14,829 --> 00:00:20,066 all you have to do is urinate on wheat and barley seeds, and wait. 4 00:00:20,066 --> 00:00:23,668 If either sprouts, congratulations, you're pregnant! 5 00:00:23,668 --> 00:00:28,962 And if wheat sprouts faster, it's a girl, but if barley, it's a boy. 6 00:00:28,962 --> 00:00:32,404 In 1963, a small study reproduced this test 7 00:00:32,404 --> 00:00:37,097 and found that it predicted pregnancy with a respectable 70% accuracy, 8 00:00:37,097 --> 00:00:40,752 though it couldn't reliably tell the sex of the baby. 9 00:00:40,752 --> 00:00:43,396 Scientists hypothesized that the test worked 10 00:00:43,396 --> 00:00:46,561 because pregnant women's urine contains more estrogen, 11 00:00:46,561 --> 00:00:48,750 which can promote seed growth. 12 00:00:48,750 --> 00:00:52,091 Now it's easy to take this ancient method for granted 13 00:00:52,091 --> 00:00:57,138 because modern pregnancy tests give highly accurate results within minutes. 14 00:00:57,138 --> 00:00:59,050 So how do they work? 15 00:00:59,050 --> 00:01:03,228 Over-the-counter pregnancy tests are all designed to detect one thing: 16 00:01:03,228 --> 00:01:05,888 a hormone called HCG. 17 00:01:05,888 --> 00:01:09,300 HCG is produced in the earliest stages of pregnancy 18 00:01:09,300 --> 00:01:10,870 and starts a game of telephone 19 00:01:10,870 --> 00:01:15,015 that tells the body not to shed the inner lining of the uterus that month. 20 00:01:15,015 --> 00:01:16,649 As the pregnancy progresses, 21 00:01:16,649 --> 00:01:19,799 HCG supports the formation of the placenta, 22 00:01:19,799 --> 00:01:23,653 which transfers nutrients from mother to fetus. 23 00:01:23,653 --> 00:01:28,090 The test starts when urine is applied to the exposed end of the strip. 24 00:01:28,090 --> 00:01:30,850 As the fluid travels up the absorbent fibers, 25 00:01:30,850 --> 00:01:35,366 it will cross three separate zones, each with an important task. 26 00:01:35,366 --> 00:01:38,995 When the wave hits the first zone, the reaction zone, 27 00:01:38,995 --> 00:01:44,993 Y-shaped proteins called antibodies will grab onto any HCG. 28 00:01:44,993 --> 00:01:47,810 Attached to these antibodies is a handy enzyme 29 00:01:47,810 --> 00:01:53,623 with the ability to turn on dye molecules, which will be crucial later down the road. 30 00:01:53,623 --> 00:01:56,586 Then the urine picks up all the AB1 enzymes 31 00:01:56,586 --> 00:02:00,849 and carries them to the test zone, which is where the results show up. 32 00:02:00,849 --> 00:02:03,879 Secured to this zone are more Y-shaped antibodies 33 00:02:03,879 --> 00:02:08,883 that will also stick to HCG on one of its five binding sites. 34 00:02:08,883 --> 00:02:12,223 Scientists call this type of test a sandwich assay. 35 00:02:12,223 --> 00:02:19,068 If HCG is present, it gets sandwiched between the AB1 enzyme and AB2, 36 00:02:19,068 --> 00:02:20,930 and sticks to the test zone, 37 00:02:20,930 --> 00:02:24,240 allowing the attached dye-activating enzyme to do its job 38 00:02:24,240 --> 00:02:26,615 and create a visible pattern. 39 00:02:26,615 --> 00:02:31,621 If there's no HCG, the wave of urine and enzymes just passes on by. 40 00:02:31,621 --> 00:02:36,446 Finally, there's one last stop to make, the control zone. 41 00:02:36,446 --> 00:02:38,398 As in any good experiment, 42 00:02:38,398 --> 00:02:41,621 this step confirms that the test is working properly. 43 00:02:41,621 --> 00:02:44,926 Whether the AB1 enzymes never saw HCG, 44 00:02:44,926 --> 00:02:48,744 or they're extras because Zone 1 is overstocked with them, 45 00:02:48,744 --> 00:02:53,626 all the unbound AB1 enzymes picked up in Zone 1 should end up here 46 00:02:53,626 --> 00:02:55,743 and activate more dye. 47 00:02:55,743 --> 00:03:00,082 So if no pattern appears, that indicates that the test was faulty. 48 00:03:00,082 --> 00:03:03,453 These tests are pretty reliable, but they're not failproof. 49 00:03:03,453 --> 00:03:05,336 For instance, false negatives can occur 50 00:03:05,336 --> 00:03:09,639 if concentrations of HCG aren't high enough for detection. 51 00:03:09,639 --> 00:03:13,501 After implantation, HCG levels double every two to three days, 52 00:03:13,501 --> 00:03:16,453 so it may just be too early to tell. 53 00:03:16,453 --> 00:03:18,519 And beverages can dilute the urine sample, 54 00:03:18,519 --> 00:03:22,878 which is why doctors recommend taking the test first thing in the morning. 55 00:03:22,878 --> 00:03:27,374 On the other hand, false positives can come from other sources of HCG, 56 00:03:27,374 --> 00:03:30,456 like IBF injections, ectopic pregnancies, 57 00:03:30,456 --> 00:03:34,440 or certain cancers such as uterine cancer or testicular cancer, 58 00:03:34,440 --> 00:03:39,482 making it possible for one of these tests to tell a man he's pregnant. 59 00:03:39,482 --> 00:03:43,848 The best way for a woman to find out for sure is at the doctor's office. 60 00:03:43,848 --> 00:03:46,373 The doctor's are also looking for HCG, 61 00:03:46,373 --> 00:03:49,802 but with tests that are more sensitive and quantitative, 62 00:03:49,802 --> 00:03:54,530 which means they can determine the exact level of HCG in your blood. 63 00:03:54,530 --> 00:03:56,936 A few minutes can feel like forever 64 00:03:56,936 --> 00:04:00,209 when you're waiting on the results of a pregnancy test. 65 00:04:00,209 --> 00:04:04,548 But in that brief time, you're witnessing the power of the scientific method. 66 00:04:04,548 --> 00:04:07,211 That one little stick lets you ask a question, 67 00:04:07,211 --> 00:04:09,277 perform a controlled experiment, 68 00:04:09,277 --> 00:04:13,058 and then analyze the results to check your original hypothesis. 69 00:04:13,058 --> 00:04:17,455 And the best part is you won't even have to wait until the next harvest.