0:00:08.119,0:00:11.229
Muscles and joints shift and jostle.

0:00:11.229,0:00:16.658
The heart’s pounding rhythm speeds up. [br]Blood roars through arteries and veins.

0:00:16.658,0:00:21.028
Over the course of a pregnancy, [br]every organ in the body changes.

0:00:21.028,0:00:23.514
Ignited by a range of hormones,

0:00:23.514,0:00:26.937
these changes begin [br]as soon as pregnancy begins.

0:00:30.384,0:00:36.238
Just days after fertilization, the embryo [br]implants in the lining of the uterus.

0:00:36.238,0:00:39.608
Because its DNA doesn’t exactly match [br]the mother’s,

0:00:39.608,0:00:43.510
the immune system should theoretically [br]recognize it as an invader,

0:00:43.510,0:00:48.417
attack, and destroy it, like it would [br]bacteria or other harmful microbes.

0:00:48.417,0:00:51.577
That’s the challenge: [br]the mother’s immune system

0:00:51.577,0:00:57.083
needs to protect both her and the fetus, [br]but can’t act as it usually does.

0:00:57.083,0:01:01.053
What happens is not as simple [br]as decreasing the immune response.

0:01:01.053,0:01:06.144
Instead, it’s a complex interaction [br]we’re just beginning to understand,

0:01:06.144,0:01:08.984
involving many different types [br]of immune cells—

0:01:08.984,0:01:13.523
some of which seem to protect the fetus [br]from attack by other immune cells.

0:01:15.977,0:01:20.537
The body also creates an antibacterial [br]plug made of mucus on the cervix,

0:01:20.537,0:01:24.512
which keeps germs away [br]and stays sealed until labor.

0:01:24.512,0:01:26.096
As a pregnancy progresses,

0:01:26.096,0:01:30.076
the uterus expands upward and outward [br]with the growing fetus.

0:01:30.076,0:01:33.806
To make room, hormones [br]called progesterone and relaxin

0:01:33.806,0:01:36.347
signal muscles to loosen.

0:01:36.347,0:01:41.208
The muscles that propel food and waste [br]through the digestive tract also loosen,

0:01:41.208,0:01:42.638
which makes them sluggish,

0:01:42.638,0:01:46.777
causing constipation as passage [br]through the tract slows down.

0:01:46.777,0:01:48.826
Loosened muscles [br]at the top of the stomach

0:01:48.826,0:01:52.147
might allow acid to escape [br]into the esophagus and throat,

0:01:52.147,0:01:54.347
causing heartburn and reflux.

0:01:54.347,0:01:56.607
These changes can worsen morning sickness,

0:01:56.607,0:02:03.121
which is caused in part by hormone HCG— [br]and can also happen at other times of day.

0:02:03.121,0:02:06.091
As the uterus grows, [br]it pushes on the diaphragm,

0:02:06.091,0:02:10.487
the muscle that expands and contracts [br]the chest with each breath.

0:02:10.487,0:02:12.917
This limits the diaphragm’s range.

0:02:12.917,0:02:17.592
To compensate, the hormone progesterone [br]acts as a respiratory stimulant,

0:02:17.592,0:02:21.317
making the pregnant woman breathe [br]faster so both she and the baby

0:02:21.317,0:02:25.122
can both get enough oxygen [br]with less lung capacity.

0:02:25.122,0:02:29.222
This all may leave the pregnant woman [br]feeling short of breath.

0:02:29.222,0:02:32.702
Meanwhile, the kidneys [br]make more erythropoietin,

0:02:32.702,0:02:35.812
a hormone that increases [br]red blood cell production.

0:02:38.901,0:02:43.690
The kidneys also keep extra water and salt[br]rather than filtering it out into urine

0:02:43.690,0:02:46.420
to build up the volume of the blood.

0:02:46.420,0:02:50.892
A pregnant woman’s blood volume [br]increases by 50% or more.

0:02:50.892,0:02:52.399
But it’s also a bit diluted,

0:02:52.399,0:02:56.384
because it only has 25% [br]more red blood cells.

0:02:56.384,0:03:00.214
Usually, the body makes blood cells [br]using iron from our food.

0:03:00.214,0:03:04.154
But during pregnancy, the fetus [br]is also building its own blood supply

0:03:04.154,0:03:06.014
from nutrients in the mother’s food—

0:03:06.014,0:03:09.284
leaving less iron and other nutrients [br]for the mother.

0:03:09.284,0:03:12.304
The heart has to work extra hard [br]to pump all this blood

0:03:12.304,0:03:14.444
through the body and placenta.

0:03:14.444,0:03:16.834
A pregnant woman’s heart rate increases,

0:03:16.834,0:03:21.334
but we don’t fully understand how blood [br]pressure changes in a healthy pregnancy—

0:03:21.334,0:03:23.401
an important area of research,

0:03:23.401,0:03:25.904
because some of the most serious [br]complications

0:03:25.904,0:03:29.274
are related to the heart [br]and blood pressure.

0:03:29.274,0:03:31.921
The expanding uterus may press on veins—

0:03:31.921,0:03:35.191
causing fluid buildup [br]in the legs and feet.

0:03:35.191,0:03:38.851
If it presses on a large vein [br]called the inferior vena cava,

0:03:38.851,0:03:41.949
it might interfere with blood [br]returning to the heart,

0:03:41.949,0:03:46.608
causing a dizzying drop in blood pressure [br]after standing for too long.

0:03:46.608,0:03:51.220
Some of these changes start [br]to reverse even before birth.

0:03:51.220,0:03:54.670
Shortly before delivery, [br]the fetus drops down,

0:03:54.670,0:03:56.941
decreasing the pressure on the diaphragm

0:03:56.941,0:04:00.911
and allowing the pregnant woman [br]to take deeper breaths.

0:04:00.911,0:04:02.491
During labor and birth,

0:04:02.491,0:04:05.721
much of the extra fluid in the body [br]is lost when the water breaks.

0:04:08.612,0:04:13.232
The uterus shrinks back down [br]in the weeks after birth.

0:04:13.232,0:04:16.545
Like the rest of the body, [br]pregnancy affects the brain—

0:04:16.545,0:04:20.246
but its effects here are some [br]of the least understood.

0:04:20.246,0:04:23.096
Recent studies show differences [br]in brain scans

0:04:23.096,0:04:25.606
after pregnancy and early parenting,

0:04:25.606,0:04:28.706
and suggest that these changes [br]are adaptive.

0:04:28.706,0:04:31.736
That means they could help [br]with parenting skills,

0:04:31.736,0:04:37.505
such as an increased ability to read [br]facial cues since babies can’t talk.

0:04:37.505,0:04:41.085
The lack of information about pregnancy’s [br]effects on the brain

0:04:41.085,0:04:47.174
highlights a general truth: historically, [br]almost all the research around pregnancy

0:04:47.174,0:04:51.044
has focused on the fetus, [br]rather than pregnant women.

0:04:51.044,0:04:53.775
Experiences of pregnancy vary widely,

0:04:53.775,0:04:56.245
both within the range [br]of healthy pregnancies

0:04:56.245,0:05:01.711
and due to complicating health conditions—[br]new research will help us understand why,

0:05:01.711,0:05:05.271
and develop effective treatments [br]where necessary.

0:05:05.271,0:05:08.545
In the meantime, [br]every pregnancy is different,

0:05:08.545,0:05:12.269
and it’s important to consult a doctor [br]with any specific questions.

0:05:13.189,0:05:16.779
Today, we’re turning an exciting corner,

0:05:16.779,0:05:21.723
as more research is devoted [br]to the astounding biology of pregnancy.