pregnancy is the development of
offspring inside a woman's uterus it's
also called gestation and during
gestation a lot of changes occur in
mom's body
so the average pregnancy lasts about 38
and a half weeks and for ease of
discussion when we're talking about
pregnancy we sort of talk about it as
having three phases called trimesters
and each trimester lasts about 13 weeks
so if i said that event x happens in the
first trimester you'd know i meant
sometime between
1 and 13 weeks of pregnancy and if event
y happens in the second trimester that
would be between weeks 14 and 26 and so
on so three trimesters so during the
second and third trimesters
the fetus is sort of getting a lot
bigger and more developed and so the
mother's uterus has to expand to
accommodate the growing fetus and
actually both the fetal growth and the
uterine growth cause a lot of
physiological change in the mom
so before we go on to talk about some of
the non-reproductive system
physiological changes in the mother you
must be wondering well how exactly does
the uterus grow so much so let's take a
look at that first so it's really
important to note that basically all of
the maternal changes that happen during
pregnancy including this this uterine
growth can be attributed in some way to
hormones especially to the ones we
classically think of as those female sex
hormones the the estrogen and the
progesterone hcg or human chorionic
gonadotropin from the embryo that plays
a pretty big role as well so at the
start of pregnancy until about week 12
so almost till the end of the first
trimester the corpus luteum in the ovary
produces most of the estrogen and
progesterone that initially support the
embryo
and and cause the development of the
placenta but during the first part of
the second trimester the corpus luteum
degenerates and the placenta takes over
as the primary hormone producer as the
as the new major endocrine organ of of
the pregnancy and remember endocrine
organs secrete hormones to to regulate
body function
so the placenta takes over as the major
endocrine organ and it starts to create
estrogen that'll actually have some
major effects in both the mother and the
fetus and actually the placenta just
kind of keeps pumping out estrogen
throughout the pregnancy so the estrogen
levels just continually rise until the
end of the pregnancy at around the 38
and a half week point
so all this estrogen around what exactly
is it doing why is it necessary
well i'll just mention a few reasons
first it's suppressing fsh and lh
release from the anterior pituitary by
negative feedback
this is really important because what
happens when fsh and lh are floating
around in the blood
well we start getting development of
follicles and eggs in the ovaries right
and we can't really afford to have
ovulation happening during a pregnancy
the the mother already sort of has
enough on her to do list with supporting
an existing pregnancy
second the high levels of estrogen are
really important in inducing growth of
the fetus's organ systems like like the
fetal lungs and liver
third the estrogen sort of stimulates
maternal tissue growth so the uterus
enlarges to accommodate the growing
fetus and and the ducts and the mammary
glands and the breasts expand and branch
in in preparation for lactation and
breastfeeding
so that's estrogen during pregnancy
the anterior pituitary gland gets a
little bit bigger during pregnancy as
well and it starts to make more
thyrotropin among other things
thyrotropin affects the thyroid gland
and increases mom's metabolic rate and
that in turn increases her appetite and
can cause the hot flashes associated
with pregnancy
and the reason mom's metabolic rate and
her appetite increase is because it
takes a lot of energy to support
gestation and so it's important that mom
gets enough food to meet those increased
energy needs
there are some other major physiologic
changes that happen too though
for example in the circulatory system
blood volume has to increase by an extra
one to two liters of blood to make sure
the fetus is nourished properly so
because of this extra blood volume the
mother's blood pressure and pulse rise
during pregnancy
and also as the uterus grows it
eventually will compress the pelvic
blood vessels underneath it and that
will obstruct venous return to the heart
from the pelvis and the legs and so
among other conditions this can cause
varicose veins to develop
there are some skin changes as well
the expanding uterus also stretches the
overlying dermis on the abdomen dermis
meaning skin
and when the dermis gets stretched too
far beyond what it can handle connective
tissue within and underneath the dermis
can tear and cause striae or stretch
marks
so typically you'll see these ready
purpley striae in places that get
stretched during pregnancy so besides
the abdomen you might see these striae
on the breasts on the thighs and on the
hips
they usually fade to a pretty faint
color a few months after childbirth
though
the lungs have a bit more work to do
during pregnancy as well
in fact they've got to work about 50
percent harder
and this is to provide oxygen to all
that extra blood that mom's got on board
for the fetus but to sort of complicate
things a bit the growing uterus pushes
up on mom's diaphragm preventing her
from taking in full breaths
so she might develop a bit of shortness
of breath during the later trimesters
the uterus puts a bit of pressure on the
stomach as well and that can cause some
heartburn or gastric reflux in mom but
luckily in the last few weeks of
pregnancy the fetus sort of descends a
bit in the pelvis and that reduces the
upward pressure on the diaphragm so mom
can breathe a bit better and the and the
heartburn typically goes away as well
the flip side of this though is that the
uterus because it's dropped a bit it
then puts even more pressure on the
urinary bladder and that leads to
needing to urinate a lot more frequently
we haven't really talked about the
weight gain in pregnancy and there's a
fair amount of extra weight that the
mother has to sort of lug around with
her and the weight gain during pregnancy
comes from a few different things
the growing fetus is generally the
biggest portion of it about seven to
eight pounds
the placenta and the amniotic fluid add
about six pounds and the extra breast
tissue adds about three to four pounds
the growth of the uterus itself adds
about four pounds and the extra blood
volume adds about 4 pounds as well
actual fat or adipose tissue gain varies
the most but but only really needs to be
between 3 and 10 pounds
so the total typical weight gain during
pregnancy is somewhere around 25 to 35
pounds
so those are some of the major body
system changes that happen in mom's body
during pregnancy