0:37:46.270,0:37:52.498 Once inside the cervix, the sperm continue on their journey. 0:37:52.498,0:37:55.363 Some remain here, perhaps to provide a back-up 0:37:55.363,0:38:01.622 for those that continue on. 0:38:01.622,0:38:05.588 The rest proceed up through the cavity of the uterus 0:38:05.588,0:38:12.880 in search of the egg. 0:38:16.926,0:38:24.498 Their number is noticeably reduced. 0:38:31.120,0:38:33.498 Here from inside the uterus, 0:38:33.498,0:38:40.558 we see the openings to the two fallopian tubes. 0:38:42.208,0:38:47.590 The sperm swim toward them. 0:38:49.622,0:38:54.498 One leads to the waiting egg. 0:38:54.498,0:38:59.861 The other to an empty tube. 0:39:01.862,0:39:04.588 Only half of the few remaining sperm 0:39:04.588,0:39:10.769 will swim up the tube that holds the egg. 0:39:29.865,0:39:33.268 The tubes are lined with millions of tiny cilia, 0:39:33.268,0:39:35.708 the same cilia which helped draw the egg 0:39:35.708,0:39:40.268 from the ovary toward the uterus at ovulation. 0:39:40.268,0:39:42.529 These cilia sway constantly, 0:39:42.529,0:39:45.498 creating a gentle downward current 0:39:45.498,0:39:52.238 that the sperm must swim against. 0:39:58.620,0:40:01.161 Some sperm get stuck in among the cells 0:40:01.161,0:40:07.329 lining the walls of the tube. 0:40:07.329,0:40:14.738 Others lose their sense of direction. 0:40:18.419,0:40:21.119 During this part of the sperm's journey 0:40:21.119,0:40:24.590 the layer of enzyme inhibitors, at the tips of their heads 0:40:24.590,0:40:28.799 is slowly being worn away. 0:40:28.799,0:40:31.968 The sperm are fully capacitated and able to fertilize 0:40:31.968,0:40:39.329 the egg, if they ever encounter it. 0:40:48.620,0:40:51.391 Of the two hundred million sperm that begin 0:40:51.391,0:40:53.150 this long journey 0:40:53.150,0:41:00.317 only about 50 ever reach the egg. 0:41:02.238,0:41:05.362 The egg is surrounded by 2 layers of the nutritive 0:41:05.362,0:41:07.862 cells which have nourished it on its journey 0:41:07.862,0:41:12.833 in the fallopian tube. 0:41:13.653,0:41:17.298 The sperm immediately release their digestive enzymes 0:41:17.298,0:41:20.921 to break through these protective, nutritive layers 0:41:20.921,0:41:27.088 in order the reach the egg itself. 0:41:27.798,0:41:31.149 At best, only one will eventually enter and 0:41:31.149,0:41:36.738 fertilize the egg. 0:41:39.208,0:41:43.359 The joint force of their exertions starts the egg 0:41:43.359,0:41:51.210 rolling around, like a mysterious, celestial body. 0:42:27.389,0:42:30.468 All the while, the sperm are dissolving their way 0:42:30.468,0:42:37.152 through the egg's outer layers. 0:42:41.214,0:42:44.212 The first sperm to reach the egg's membrane 0:42:44.212,0:42:50.208 is immediately drawn inside. 0:42:50.208,0:42:52.968 This is the tail of the penetrating sperm 0:42:52.968,0:42:55.391 seen from the surface of the egg at enormous 0:42:55.391,0:43:01.921 magnification. 0:43:01.921,0:43:07.891 And this is a picture from inside the egg itself. 0:43:07.891,0:43:16.119 It has been fertilized now for only a fraction of a second. 0:43:16.119,0:43:18.589 Here is the penetrating sperm with a circle 0:43:18.589,0:43:19.394 around it 0:43:19.394,0:43:22.563 from a wider perspective. 0:43:22.563,0:43:26.968 Only this single sperm will be allowed inside the egg. 0:43:26.968,0:43:29.712 A rapid, biochemical change took place in the 0:43:29.712,0:43:31.711 egg's membrane. 0:43:31.711,0:43:37.318 It is now impermeable to all other sperm. 0:43:37.318,0:43:39.833 Once inside the sperm too undergoes a 0:43:39.833,0:43:43.397 dramatic transformation. 0:43:43.397,0:43:47.911 It loses its mid-piece and tail. 0:43:47.911,0:43:54.238 The tailless head spells up almost like rising bread. 0:43:54.238,0:43:56.382 This hole in the sperm head's covering 0:43:56.382,0:43:59.768 is the first indication that it's about to rupture 0:43:59.768,0:44:04.060 and release its precious genetic material. 0:44:04.060,0:44:07.362 Here, the first strand of genes is making its way 0:44:07.362,0:44:12.228 out of the sperm into the egg. 0:44:12.228,0:44:14.968 The genetic material continues to spill out 0:44:14.968,0:44:16.798 from the sperm head. 0:44:16.798,0:44:19.998 Its tightly packed molecules contain the father's 0:44:19.998,0:44:23.219 hereditary message. 0:44:23.219,0:44:25.395 They almost seem to have been dispersed by 0:44:25.395,0:44:31.802 an explosive force. 0:44:31.802,0:44:36.468 This is an extreme close-up of the genetic material itself. 0:44:36.468,0:44:39.240 The magnification on the television screen is over 0:44:39.240,0:44:45.120 half a million times. 0:44:45.120,0:44:47.185 The genetic material of the mother's egg 0:44:47.185,0:44:48.709 and the father's sperm 0:44:48.709,0:44:51.118 combine. 0:44:51.118,0:44:58.740 Two cells have joined to make a single new cell. 0:44:59.153,0:45:06.143 And within 24 hours that new cell begins to divide. 0:45:06.258,0:45:09.028 These early cell divisions of the human embryo 0:45:09.284,0:45:13.074 have never before been filmed. 0:45:15.986,0:45:19.315 The fertilized egg now has 2 nuclei, 0:45:19.315,0:45:24.965 the small indentations at the center of the cell. 0:45:26.076,0:45:30.756 The first division of the egg is beginning. 0:45:37.802,0:45:41.292 Now there are 2 identical cells, 0:45:41.923,0:45:44.353 still within the same nourishing material 0:45:44.406,0:45:46.256 of the original egg. 0:45:46.497,0:45:48.071 No growth has occurred, 0:45:48.071,0:45:52.191 but, rather, a distinction between cells. 0:45:53.397,0:45:55.697 Once it has begun to divide 0:45:55.707,0:45:59.817 the fertilized egg is called a zygote. 0:46:07.834,0:46:12.074 Now there are 4 cells. 0:46:19.351,0:46:22.901 The divisions happen at such an accelerated pace 0:46:22.967,0:46:25.801 that there's little opportunity for the new cells 0:46:25.801,0:46:29.951 to grow before they divide again. 0:46:42.278,0:46:46.558 Now there are 8 cells. 0:46:54.667,0:46:57.910 Each new generation of cells of the zygote is 0:46:57.910,0:47:02.080 smaller than the one before it. 0:47:19.901,0:47:22.397 Another division, 0:47:23.049,0:47:27.229 and another. 0:47:29.514,0:47:32.824 As the zygote divides, it moves along the tube 0:47:33.052,0:47:37.351 toward the uterus. 0:47:39.220,0:47:41.735 Now it has become a dense, compact cluster 0:47:41.735,0:47:46.871 of many cells. 0:47:48.574,0:47:54.826 And after 5 days it is called a blastocyst. 0:47:54.826,0:47:59.205 It is still no bigger than the original egg. 0:47:59.205,0:48:05.717 Its center is filled with liquid. 0:48:08.629,0:48:11.307 Within 10 days of fertilization, 0:48:11.307,0:48:13.492 the blastocyst implants itself firmly 0:48:13.492,0:48:16.018 in the lining of the uterus. 0:48:16.018,0:48:18.007 Already the mother's hormones are directing 0:48:18.007,0:48:19.659 changes in her body 0:48:19.659,0:48:25.023 to prepare it to support the growing embryo. 0:48:25.023,0:48:27.261 Barely visible to the naked eye, 0:48:27.261,0:48:30.629 the embryo will be nourished by the lining of the uterus, 0:48:30.629,0:48:35.483 and then by the placenta. 0:48:35.483,0:48:40.007 After 2 weeks, the embryo is elongated. 0:48:40.007,0:48:48.809 It is barely one tenth of an inch long. 0:48:50.223,0:48:58.402 At the top, what will become its head and brain. 0:49:01.116,0:49:04.131 Below, at the tail, the embryo is firmly attached 0:49:04.131,0:49:09.399 to the placenta, which will nourish it. 0:49:10.446,0:49:13.566 At 4 weeks, the embryo has arm buds and 0:49:13.566,0:49:18.923 is distinctly curled. 0:49:18.923,0:49:25.096 It has the beginning of eyes. 0:49:29.097,0:49:34.870 At 5 weeks, the nose begins to take shape. 0:49:34.870,0:49:38.597 At 6 weeks, leg buds are apparent. 0:49:38.597,0:49:42.668 The embryo is less than half an inch long. 0:49:42.668,0:49:47.007 It floats inside the fluid-filled amniotic sac. 0:49:47.007,0:49:51.905 Its spine is clearly visible. 0:49:51.905,0:50:01.445 At 7 weeks, the embryo is three quarters of an inch long. 0:50:02.128,0:50:04.186 It can move its hands on which there are 0:50:04.186,0:50:10.006 clearly defined fingers. 0:50:14.746,0:50:21.777 Its internal organs are visible. 0:50:23.339,0:50:30.389 The eyelids are formed. 0:50:30.489,0:50:33.155 The skull bones, rich in blood vessels, 0:50:33.155,0:50:35.531 are growing together at an angle at the 0:50:35.531,0:50:40.627 crown of the head. 0:50:40.627,0:50:43.036 At 8 weeks, the fingers of the hand are 0:50:43.036,0:50:45.538 well defined. 0:50:45.538,0:50:56.135 And the toe joints of the feet are clearly visible. 0:50:56.135,0:51:01.372 At about 10 weeks, the embryo is considered a fetus. 0:51:01.372,0:51:04.205 It can move actively. 0:51:04.205,0:51:08.130 There is a suggestion of an ear. 0:51:08.130,0:51:10.445 It is two inches long. 0:51:10.445,0:51:15.837 And it still has the stub of a tail. 0:51:15.837,0:51:21.706 At 11 weeks, it is two and a half inches long. 0:51:21.706,0:51:27.192 At 12 weeks, it is 3 inches long. 0:51:27.192,0:51:30.237 Here-the umbilical cord-connecting the fetus 0:51:30.237,0:51:34.245 to its food supply. 0:51:34.245,0:51:38.475 By 14 weeks, it can bring its hands together. 0:51:38.475,0:51:44.390 And suck its thumb. 0:51:44.390,0:51:47.805 By 15 weeks, the sensory organs are nearly 0:51:47.805,0:51:51.513 completely formed. 0:51:51.513,0:51:57.643 And by 16 weeks, it is actively turning inside the mother. 0:52:05.718,0:52:10.343 This fetus is 18 weeks old. 0:52:10.343,0:52:12.813 It is five and a half inches long. 0:52:12.813,0:52:14.798 And is here shown, 15 times larger than its 0:52:14.798,0:52:22.020 actual size. 0:52:22.796,0:52:25.326 Its mouth and lips are fully formed. 0:52:25.326,0:52:27.388 And it has the strange nasal plugs 0:52:27.388,0:52:31.747 whose purpose is not yet understood. 0:52:31.747,0:52:34.103 The eyes of the fetus are closed, 0:52:34.103,0:52:38.283 but it can see. 0:52:38.835,0:52:42.099 (pulsing sound) 0:52:42.122,0:52:44.587 This sound is made by the fetus as it 0:52:44.673,0:52:47.015 breathes in the amniotic fluid 0:52:47.135,0:52:50.455 in what is known as fetal respiration. 0:52:50.533,0:52:53.893 It brings the fluid in through its mouth, 0:52:53.946,0:52:58.046 and then breathes it out again. 0:53:09.508,0:53:12.886 The umbilical cord is the fetus' link to its 0:53:12.886,0:53:20.297 source of life, the mother. 0:53:20.297,0:53:26.466 Here are the fetus' sex organs. 0:53:27.830,0:53:32.083 All its important physiological systems have developed. 0:53:32.083,0:53:34.751 But it will be at least another 8 weeks before the 0:53:34.751,0:53:37.660 fetus has even a remote chance of surviving 0:53:37.660,0:53:41.706 outside its mother's womb. 0:53:53.266,0:53:55.614 Whatever signals the beginning of birth 0:53:55.614,0:53:57.477 is till a mystery. 0:53:57.477,0:54:00.113 But when the fetus is ready to be born, 0:54:00.113,0:54:03.984 the uterus begins its powerful contractions. 0:54:03.984,0:54:09.175 And the process of birth begins. 0:54:12.536,0:54:13.914 "Pull your legs right in. 0:54:13.914,0:54:16.144 Keep it coming. 0:54:16.144,0:54:19.681 Take another quick breath. 0:54:19.681,0:54:20.481 Hold it. 0:54:20.481,0:54:24.903 Push. 0:54:24.903,0:54:28.210 Don't stop. 0:54:28.210,0:54:30.465 One more. 0:54:30.465,0:54:31.400 Deep breath. 0:54:31.400,0:54:33.526 Push....push. 0:54:33.526,0:54:37.706 That a girl. 0:54:37.706,0:54:43.323 Can you see this baby's head?" 0:54:43.323,0:54:44.915 "Ok, now, stop pushing.' 0:54:51.645,0:54:55.358 "Oh, beautiful job." 0:54:55.358,0:54:56.583 "Here he is... 0:54:56.583,0:54:58.558 suck out his little nose and mouth 0:54:58.558,0:55:01.355 so he can take his nice, clean, first breath. 0:55:06.665,0:55:10.675 Nothing's little about this baby." 0:55:10.675,0:55:16.384 (baby cries) 0:55:16.384,0:55:18.009 "Congratulations!" 0:55:18.009,0:55:21.474 "Another girl!" 0:55:21.474,0:55:34.854 (baby cries) 0:55:34.854,0:55:38.883 "Happy birthday."