El proceso de desarrollo que experimentan los embriones de embarazos múltiples en el útero está lleno de complicaciones y peligros. Pero resulta fascinante observar cómo un ser humano interactúa por primera vez con sus iguales antes de cruzar el umbral del útero materno. En el vientre materno: gemelos, trillizos y cuatrillizos hace el seguimiento de una pareja de gemelos bivitelinos (o mellizos) y de otra de univitelinos (o idénticos), de un embarazo de trillizos y de la rareza de unos cuatrillizos idénticos que luchan por su supervivencia. Gracias a la tecnología más avanzada con imágenes en 4-D generadas a través de ultrasonidos, somos testigos de la interacción de los fetos antes del nacimiento: se estiran, se empujan, se acarician y se dan patadas en una especie de juego prenatal que puede prolongarse tras el nacimiento.
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00:00But in this case, something even more extraordinary happens.
00:05The fertilized egg splits in two, creating two twins.
00:10The fertilized egg is born.
00:15The fertilized egg is born.
00:20The fertilized egg is born.
00:26The fertilized egg splits in two, creating two identical twins.
00:33Then each one splits again.
00:36Something that happens once every 64 million.
00:42They are identical quads.
00:47For the first time, the new and revolutionary techniques of creating images
00:52allow us to follow in detail three very different pregnancies.
01:00Identical twins.
01:04Triplets conceived on different days.
01:09And some spectacular quadruplets.
01:15Through them, we will delve into the greatest wonder in the history of human reproduction science.
01:22The miracle of multiple births.
01:27In the mother's womb.
01:45Twins, triplets and quadruplets.
01:55This girl is about to be born.
02:01But for her, her stay in the mother's womb has not been a pleasant journey.
02:08After her birth, it will not be the first time she meets other humans.
02:18She has been sharing her space not with one, but with three sisters.
02:31Each grew up from a smaller egg than a grain of sand.
02:38Lonely and ignorant.
02:43They have been touching each other.
02:46Reacting to each other.
02:51Even doing something that looks like a kiss.
02:58They have all fought for space and sustenance.
03:05However, they have laid the foundations for a life of warmth, comfort and companionship.
03:15They have also helped each other.
03:18And they have forged a connection and some patterns of conduct that will define them for the rest of their lives.
03:35As for most of us, the journey begins with the act of conception.
03:44During which an adult and healthy male releases approximately 300 million sperm in the woman's vagina.
03:56The sperm will go through the reproductive tract towards the fallopian tubes.
04:01Where the prize is.
04:05An egg without fertilization.
04:08During its reproductive cycle, a woman usually releases an egg.
04:15The first sperm that reaches it and manages to enter through its outer layer will be the winner.
04:27Once inside, the sperm head, which contains the father's DNA, and the nucleus of the egg, where the mother's DNA is,
04:36join through small fibers called centrosomes.
04:45The two DNA games merge.
04:49The conception has taken place.
04:54And this is the first cell of what will be a new human being.
05:02Day 1.
05:04In its first hours, the fertilized egg begins its journey down through the fallopian tube towards the uterus.
05:13A day later, it has already been subdivided once.
05:19The second day we have between two and four cells.
05:25The third, eight.
05:31Day 5.
05:32The fifth day, the embryo, which is now called blastocyst, has between 70 and 120 cells distributed in two differentiated sections.
05:43The inner cellular mass will be the body.
05:48The exterior, which is ring-shaped and is called trophectoderm, will become the placenta.
05:55A vital part.
06:02Around the sixth day, the blastocyst finally comes out of the shell of the egg and adheres to the uterus, where it begins to grow.
06:15Here it will remain for the next 39 weeks, going from blastocyst to embryo.
06:23From embryo to fetus.
06:27And from fetus to full baby.
06:37But in a few cases, approximately one in every 250, the egg performs an extraordinary operation.
06:49It splits in two.
06:50It duplicates, giving rise to the separated fertilized eggs.
06:55Separated, but identical.
07:04No one fully understands why this happens.
07:09But the very nature of the egg could give us a clue.
07:17Most identical twins are conceived by women who are well at the beginning, well at the end of their fertile years.
07:29Some scientists believe that the ovules of older women are weaker and therefore more likely to split.
07:40What we know for sure is that this has to happen in the first 14 days after conception.
07:46Otherwise, it would not happen.
07:56Identical twins have one of the closest biological relationships known.
08:02They will grow up looking alike and having similar voices, but they are not perfect replicas.
08:11A small number of the maternal ovule's genes are located outside its nucleus.
08:19Known as mitochondrial DNA, these genes can mutate after the ovule is subdivided,
08:28subtly altering the development of the embryo.
08:34As the twins grow and reach maturity,
08:38small differences in height, constitution, and even personality will become more and more evident.
08:49This is why, nowadays, some scientists avoid the term identical,
08:54and prefer to use monozygotic twins or uniovular twins.
09:04Our uniovular identical twins settle in the ovule around the sixth day.
09:13Like the single embryos, each of them will develop inside two sacs.
09:19One outside, the corion, which is attached to the placenta,
09:24and the inside, known as the amniotic sac.
09:29Both will merge.
09:33Some twins share a corion, and very few of them have the same amnion.
09:42As they grow up, they will compete for their mother's space and nutrition.
09:48But despite this, they will also share a very deep and lasting bond.
09:55This woman, Julie, is very atypical.
10:00Although she doesn't know it, her fertilized ovule has split, not in two, but in four.
10:14She is probably one of the few pregnant women in the world with identical quadriplegics.
10:21Something that happens once every 64 million years.
10:29These tiny fetuses each have their own amnion,
10:33but they share the corion, and with it, the placenta.
10:38The consequence of this is that for 30 weeks,
10:42they will have the same source of oxygen and nutrition.
10:47From a biological point of view,
10:50they are some of the closest individuals that the human body is capable of conceiving.
11:00Rachel, another mother, will go through a totally different process.
11:06She has released two eggs.
11:09One from each ovary, fertilized by different sperm.
11:15She is pregnant with twins, also called biovulars or dizygotic.
11:23It's as if two pregnancies had started on the same day.
11:30Unlike the identical ones,
11:33the twins are not genetically more different than the siblings
11:37that share half of their genes.
11:45Rachel is a mother of four,
11:48and she is pregnant with twins.
11:52They share half of their genes.
11:59Day 7
12:01All of our ovules are implanted in the uterus.
12:07In the next few days,
12:09the blastocyte begins to enter the uterus lining,
12:14which is currently swollen by the hormones.
12:20This small army of cells invades the uterus,
12:24and little by little,
12:26its members split in two to form the primary bonds
12:29between the placenta and the bloodstream of the mother.
12:37Among the changes that occur in the blastocyte cells,
12:42the first of them is the configuration of two layers.
12:50Around the ninth day,
12:52these layers have become a disk with a cavity at the top,
12:57the future amniotic sac,
13:00and another one at the bottom, the vitelline sac.
13:09Halfway between them,
13:11a crevice called the primitive line appears.
13:16They go towards it,
13:18and over it, the cells precipitate.
13:30Two weeks later,
13:32at one end of the primitive line,
13:35another spot known as the organizer is formed.
13:40Up to this moment,
13:42the cells in the body had all been the same.
13:48They are the mother cells.
13:53Now each one flows over the organizer,
13:56who assigns them their destiny.
14:01Some will be part of a limb,
14:05some will be part of a limb,
14:07some will be part of a hand,
14:10and some will be part of a crystal eye.
14:16The crest of this little embryo
14:18does not yet look like a head.
14:21But at 15 days,
14:23the nervous cells begin to configure what will later become the brain,
14:27as well as the spinal cord.
14:31Both organs are completely exposed and unprotected by skin or bones.
14:36One of the first to form is the heart.
14:40Until now,
14:41there had been a lot of dormant muscle cells.
14:47But later,
14:48around the 22nd,
14:50a cell contracts spontaneously,
14:55and begins a chain reaction in the rest of the body.
15:00The whole body begins to beat.
15:06At first,
15:07it pumps primitive blood cells,
15:09no thicker than hair,
15:11which transports the vital food and oxygen supplies for growth.
15:17Later,
15:18when the brain has developed,
15:20it will control the rhythm of the contractions,
15:23increasing the speed when it needs more energy.
15:27And slowing down when the body rests.
15:32Throughout life,
15:33a heart beats 3 billion times.
15:46This 32-year-old woman is Jennifer.
15:51A year ago,
15:53her body created an egg that was later fertilized.
16:03Then it split in two to form identical twins.
16:09But the story doesn't end there.
16:13Later,
16:14Jennifer released another egg that was also fertilized.
16:20A third brother joined the identical twins.
16:32This process is known as super-fertilization.
16:36In Latin,
16:37it means additional fertilization.
16:42It's something very unusual.
16:47In Jennifer's case,
16:48the second egg was fertilized
16:50by the surviving sperm of the first penetration.
16:56But this is not always the case.
17:01Technically,
17:02each egg could have been fertilized by the sperm of two ejaculations.
17:08Or even different men.
17:15It is estimated that out of every 400 pairs of twins,
17:20one is made up of two siblings of different parents.
17:24Week 6.
17:26Our three groups of embryos have reached their sixth week.
17:31They measure almost two and a half centimeters.
17:35Now,
17:36the eyeball is made up of 85%.
17:40And we can see the beginning of some rudimentary crystals.
17:47In this phase,
17:48the uterus can contain many fetuses.
17:51The record is 15,
17:52although the number of live births has not exceeded 9.
17:57In this echograph,
17:58we can see five fetuses of a few weeks old.
18:04Although Jennifer's triplets were conceived naturally,
18:08perhaps as a result of a super fertilization,
18:11most of the multiple pregnancies
18:13occur thanks to modern fertility treatments.
18:21In some cases,
18:22the woman takes drugs to stimulate the production of ovules,
18:26some of which end up being fertilized through sex.
18:36In other cases,
18:37we use in vitro fertilization.
18:44Here,
18:45the ovules are fertilized outside the ovary,
18:47in a petri dish,
18:49and then they are inserted into the uterus.
18:57Since the beginning of fertility treatments in the 1970s,
19:02the number of twins has increased by 50%.
19:05And the number of triplets and quadruplets has multiplied by more than four.
19:11Second month.
19:19The embryos are eight weeks old.
19:26Now they are three centimeters long,
19:29the size of the tip of the thumb.
19:35The eyeball is finished.
19:38The crystalline almost as well,
19:40but the muscle that will allow it to function has not yet grown,
19:45and will not be useful until the sixth month.
19:52In two weeks, the fetus will have eyelids.
19:58The head,
19:59one of the first structures that grow,
20:01is huge.
20:03It is one third the size of the fetal body.
20:08The embryo begins to resemble a small human.
20:12From now on,
20:13it is known as fetus,
20:15from the Latin word that means baby.
20:24Week nine.
20:29In the ninth week, the brain develops rapidly.
20:37Each minute creates an average of two and a half million cells,
20:41which is equivalent to 100 billion at birth.
20:54It is now when the body begins to move.
21:03These movements consist of involuntary spasmodic reflexes
21:08that the brain still does not control.
21:14This phenomenon plays a vital role
21:16in stimulating muscle growth
21:18and strengthening the joints.
21:25The heart acquires greater speed.
21:29When it began to beat the third week,
21:31it was at a rate of 75 beats per minute.
21:35Gradually, the speed increases,
21:37and in the ninth week,
21:38it beats at a frenetic rate of 165 beats per minute.
21:43It is its maximum speed.
21:46During the second half of the pregnancy,
21:48its rhythm will slow down
21:50until it reaches between 125 and 150 beats per minute.
21:55A child's heart beats an average of between 70 and 100 beats per minute.
22:00An adult's heart beats between 70 and 80 beats per minute.
22:09Week ten.
22:14Between the tenth and the fourteenth week,
22:17the pregnant women undergo their first ultrasound.
22:28Ultrasounds have revolutionized our understanding of fetal development.
22:39These images are produced by high-frequency waves,
22:43too high for us to perceive,
22:47emitted from a probe into the womb.
22:58The vibrations penetrate the soft tissue,
23:01but bounce off when they collide with denser structures,
23:04such as bones.
23:06From the pattern they form,
23:08the computer creates an image of the hidden fetus.
23:15Until now, the image of the ultrasound was flat,
23:18two-dimensional.
23:20But new technology allows us to see images in three dimensions
23:24in a temporal sequence,
23:26which produces four-dimensional or 4D ultrasounds.
23:36Week eighteen.
23:41We have reached the eighteenth week,
23:43half of the gestation.
23:46At this point, we are approaching the stage
23:49when the senses of our fetuses begin to develop for real.
23:55The digestive system also begins to function.
24:00Although they receive all the support they need directly in their blood flow
24:04and through the placenta,
24:07they have to be able to swallow and digest
24:09from the moment they are born.
24:15For this reason, their mouths open
24:17and the fetuses drink part of the amniotic fluid that surrounds them.
24:26This 4D image shows their first efforts.
24:34Some of the flavors of the food consumed by the mother
24:37travel to the placenta,
24:39enter the bloodstream of the fetuses
24:42and exit the amniotic fluid.
24:54The fetuses taste,
24:56and thus develop their taste buds.
25:03With their senses developing simultaneously,
25:06the fetuses are about to use them.
25:11The twins and other babies of multiple pregnancies
25:13exhibit a particularly peculiar behavior.
25:19Scientists have witnessed them playing together.
25:30Day 20
25:33Twenty weeks have passed since the gestation.
25:38The fetuses measure 14 centimeters,
25:41so small that they fit in the palm of their mothers' hands.
25:49They still cannot open their eyes,
25:51although the structure of the eyeball is already formed.
25:56The iris, which controls the amount of light they receive,
25:59is growing,
26:01but the pupil will not form until the moment of birth is near.
26:08The fifth month is an important time for the nervous system.
26:12The number of nervous cells increases rapidly.
26:16Two and a half million new neurons every minute.
26:21100 billion at birth.
26:26Their main task is to grow,
26:31although this is about to become their biggest problem.
26:38The uterus can contain a fetus weighing up to five and a half kilos.
26:47Normally, single babies weigh between two and a half kilos
26:50and five and a half kilos at birth.
26:54Twins weigh between two and almost three kilos.
26:59And triplets between one and a half and two and a quarter.
27:05As for quadruplets,
27:07sometimes they are born weighing only one kilo each
27:10and need to spend several weeks in intensive care.
27:16The taller a woman is,
27:19the longer her abdomen and the greater the weight she can bear.
27:24Week 24.
27:26We have reached 24 weeks of development.
27:31At this time, the lungs secrete surfactant,
27:35which helps babies breathe when they are born.
27:38It is a gelatinous substance
27:40that allows the lungs to separate while inspiration occurs.
27:45Because quadruplets are almost always premature,
27:48doctors prescribe a steroid to the mother
27:51that helps the formation of the surfactant.
27:56Because quadruplets are almost always premature,
27:59doctors prescribe a steroid to the mother
28:02that helps the formation of the surfactant.
28:06But for the first time,
28:08their mother will be able to see them interact.
28:15Although only one appears on the screen,
28:18sometimes we can see the extremity of another.
28:28These 4D images show how one pushes the other.
28:40Even the twins, who are in separate corneas,
28:43feel that their brothers are taking their place.
28:53The womb is running out of space.
28:58Our twins are about to start
29:00one of the most fascinating prenatal activities.
29:05Games.
29:10And even more.
29:12Some of these games seem to continue after birth.
29:25In one case, a pair of twins used to put their cheeks together,
29:29each one to one side of their corneas.
29:41When they were a year old,
29:44their favorite game was to put each one
29:47to one side of a curtain
29:50and laugh every time they touched each other through the cloth.
29:58Scientists believe that they simply extended
30:01their prenatal behavior to early childhood.
30:06Week 26.
30:09After 26 weeks of prenatal care,
30:12the eyes suddenly open
30:14when the eyelids are separated for the first time.
30:19Some researchers believe that now the babies can see.
30:24In the dark, the fetuses could be able
30:27to distinguish the silhouettes of their siblings.
30:30However, single babies have a more limited vision.
30:33But the twins can contemplate many more things
30:36when, from time to time, the light penetrates the uterus.
30:42The middle and internal ears,
30:44which have been growing since the fourth week,
30:47are completely formed and can function.
30:52The fetuses can hear the heartbeat of their mother
30:55and the sounds of the amniotic fluid.
31:01They can also perceive the noises of the outside world,
31:05including music and voices.
31:10Week 28.
31:13We have reached the 28th week.
31:20Now, one of the things
31:22that doctors pay more attention to is the umbilical cord.
31:28This masterpiece of nature is thick and resistant.
31:34It contains two arteries and a vein,
31:37twisted in such a way that no knots are made.
31:48Even if the cord is wound around the neck,
31:51it can supply the baby with nutrients
31:55But for the twins who share the amniotic sac,
31:58this life-saving line is also a great danger.
32:04Identical twins can be trapped in the other's cord
32:08and interrupt the flow of blood and oxygen,
32:11either for themselves or for their siblings.
32:16This ultrasound shows a twisted cord.
32:31The reason identical twins
32:33who share the same amniotic sac
32:35are often illuminated by cesarean section
32:38is to reduce the risk of being trapped in the cord.
32:43In the last few weeks before birth,
32:45babies are putting on as much weight as they can.
32:49The bigger and fatter they are, the better.
32:54While doctors monitor the health of fetuses from the outside,
32:59they can also regulate and control their development
33:03by monitoring the growth of the fetus.
33:09If one of the twins does not receive enough blood in the uterus,
33:13its body will take measures to preserve its most important part,
33:17the brain.
33:22In fact, it is able to regulate the volume of blood
33:25that the different parts of its body receive.
33:29In this case, the volume of blood in the uterus
33:34is reduced by pumping less blood to the extremities,
33:36which do not need it so much,
33:38and more to the brain,
33:40to prevent it from being damaged by lack of food.
33:46Week 30
33:50At 30 weeks, the fetuses have everything in place.
33:57Some details, such as the eyelashes, have already been formed.
34:03For single babies, the last 10 weeks consist of one thing,
34:08to grow.
34:14But this is not so easy for the multiples,
34:17because there is no more space for them to grow.
34:22Babies compete for the space by pushing themselves.
34:30Their eyeballs move and react to light.
34:38If they are not able to move,
34:42they will not be able to grow.
34:49If an intense light is projected on the abdomen,
34:54it has been observed that the babies react.
35:01Week 32
35:04For single babies, they have eight weeks to go.
35:08But for our triplets, the big moment is much closer.
35:15All triplets face a medical challenge.
35:21The delicate balance between a sufficiently long pregnancy,
35:25so that they have a sufficient size at birth,
35:28but not so prolonged that it puts the mother or the babies in danger.
35:35It is essential that the lungs have matured
35:38so that the newborns can breathe for themselves.
35:4534 weeks is an ideal period for triplets.
35:53Due to the dangers of natural birth,
35:55doctors recommend a cesarean section.
36:00In the case of Jennifer,
36:01the doctors decide not to wait and opt for 32 weeks.
36:08Jennifer has chosen local anesthesia.
36:12As she does not feel pain in the abdomen,
36:14she will be conscious all the time.
36:20The surgeon prepares to perform the first incision.
36:25Inside, the babies do not know what is going to happen.
36:34Cesareans are always done quickly to reduce the risk of complications.
36:40The surgeon cuts the membrane.
36:46The first baby is born.
36:49It is one of the identical twins, a male.
36:53The baby breathes and shouts for help.
36:59The cord of the placenta,
37:01its life insurance for eight months, is cut.
37:07Without pausing, the surgeon looks for the other twin,
37:10which is in the same corionic sac.
37:17This one comes out quickly.
37:22However, the arrival of his brother is delayed
37:25because he is in his own corionic sac.
37:38Finally, he comes out. Also by the feet.
37:48Despite the abdominal pressure in recent months,
37:51the three babies are strong and healthy.
38:00They weigh them.
38:03Each of them weighs a little more than three kilos.
38:10But they are eight premature weeks.
38:18The sophisticated technology incubators
38:21imitate the welcoming world of the womb
38:23and will help them gain weight and make their lungs mature.
38:28In underdeveloped countries,
38:30babies share the incubators for warmth and comfort.
38:36Week 38.
38:40Rachel's twins are about to be born.
38:44They have spent the last 38 weeks in the womb.
38:50Their lungs are robust and their bodies are ready.
38:59At birth, twins usually weigh a little over two kilos.
39:06Their small bodies make them good candidates for a natural birth.
39:13This is what Rachel wants.
39:16She has had twins before and feels safe and able to give birth naturally.
39:26A hormone causes the birth.
39:29Normally, the baby turns its head down when the pregnancy comes to an end.
39:35With two in the womb, this is more difficult.
39:46The baby whose head is closest to the canal will be the first.
39:55Water breaks.
40:00The baby's head opens up through the remains of the bag that has protected it for nine months.
40:08With the cervix fully dilated,
40:10the uterus muscles continue to push the baby into the outside world.
40:20Rachel has been pushing for three hours.
40:25The first one peeks through the head and Rachel squeezes to get it out.
40:33As is often the case with twins,
40:35the umbilical cord is wound around the neck.
40:38The comadrona immediately unties it.
40:44The first baby is about to be born.
40:47The first baby is about to be born.
40:50The first baby is about to be born.
40:53The first baby is about to be born.
40:56The first baby is about to be born.
40:59The first baby is about to be born.
41:05It's a boy, and he weighs just over three kilos.
41:08A healthy value for a twin.
41:11A healthy value for a twin.
41:26For the first time in nine months,
41:28this baby has all the belly for himself.
41:49Ten minutes after the first birth,
41:51the second baby's head appears.
41:57He follows his brother into the outside world.
42:04It's a girl, and she weighs just over two kilos.
42:12After a few minutes of separation,
42:17the twins are twenty-nine weeks and three days old.
42:21So the doctors decide that it's time to operate
42:24before the risk is too high.
42:28All the members of the extensive medical team
42:30are focused on the mother and her imminent birth.
42:38The surgeon pulls out the abdomen
42:41and tries to locate the first baby,
42:45which opens up through her uvula.
42:58Each one has their own.
43:04It's a girl, and she weighs just over three kilos.
43:19Then comes her sister, who is just as small.
43:27The team checks each one's vital signs.
43:31Their biggest concern is that the babies
43:34can't breathe without assistance.
43:40These girls were born eleven weeks before the only babies.
43:53The doctor does the third one, the smallest one.
43:59He takes her out of the womb,
44:01and hands her over to the midwife to examine her.
44:08There's only one left.
44:11So this extraordinary quadruple birth is about to end.
44:30In the end, the fourth and last baby is born.
44:34They're all girls.
44:43It's incredible that they all weigh one kilo,
44:46a quarter of the weight of a single baby.
44:53They'll also have to spend several weeks in the incubator
44:56before they mature enough to go home.
45:09Rachel's twins are eight weeks old,
45:12but they've been together for almost a year.
45:17Each one begins to acquire their own personality.
45:23Although they're not identical twins, they're very similar.
45:27This is partly due to their genes,
45:29and partly due to the time they've spent in the womb.
45:37Although identical twins look a lot more like each other,
45:41a product of their genetic configuration,
45:43their upbringing will also play a role.
45:47Jennifer's twins are already at home.
45:50Now they can breathe on their own.
45:53At this age, they all look the same.
45:57But as they grow up,
45:59it's likely that the twins will be different from the identical ones.
46:10Julie's quadruples are three months old.
46:13They're gaining a lot of weight,
46:15even though they were born with only one kilo of weight.
46:22Julie and Jose feed them with a special milk
46:25that contains extra calories to speed up their growth.
46:30It took them four weeks to reach the average weight,
46:33only three kilos.
46:40Even today, with all the advances in medicine,
46:44quadruples are still a reproductive miracle.
46:50Although they make up a small proportion of all human births,
46:54they fascinate us all.
46:58For science, they're not just a challenge,
47:01but also a window to reproduction
47:03that provides a lot of knowledge
47:05about the amazing world of the mother's womb.
47:13And for our twins, triplets and quadruplets,
47:17the interactions with their siblings in the womb
47:20will unite and define them as they grow up,
47:23and will provide them with a source of comfort and inspiration
47:27for the rest of their lives.