The first trimester
The
first trimester lasts for the first 12 weeks of the pregnancy and is crucial
for the baby's development. At conception, the egg and sperm combine to form a
zygote, which will implant in the uterine wall.
The
zygote becomes an embryo as the cells divide and grow. All of the major organs
and structures begin to form.
At
4–5 weeks, the embryo is only 0.04 inches long but will grow to around 3 inches
long by the end of the first trimester. The embryo is now looking a lot more
like a human baby.
The
fetus's heart rate can be heard as early as 8 weeks on a doppler in the
doctor's office, but more likely closer to 12 weeks. During the eighth week the
eyelids remain closed to protect its eyes. The fetus can also make a fist at
this stage. Also, external genitalia will have formed and may be visible during
an ultrasound, meaning that a doctor can tell
someone whether the fetus is male or female.
A
woman will experience many changes during the first trimester, too. Many women
will start to feel morning sickness, or nausea and vomiting due
to pregnancy, at 6–8 weeks.
Despite
its name, this nausea does not just occur in the morning. Some pregnant women
get sick at night, while others are sick all day.
A
pregnant woman might also feel very tired and notice that she is more emotional
than usual due to hormonal changes.
Many
also report experiencing food cravings or aversions during early pregnancy,
alongside a stronger sense of smell. Breast tenderness is also very common.
The second trimester
The
second trimester lasts between week 13 and 26 of pregnancy. The fetus will go
through a lot of changes during this time and grow from approximately 4–5
inches long to around 12 inches long.
During
the second trimester, the fetus will also go from weighing about 3 ounces to
weighing 1 pound (lb) or more.
In addition
to the major structures and organs, other important parts of the body will also
form during the second trimester, including:
- the skeleton
- muscle
tissue
- skin
- eyebrows
- eyelashes
- fingernails
and toenails
- blood cells
- taste buds
- footprints
and fingerprints
- hair
If
the fetus is male, the testes begin to drop into the scrotum. If the fetus is
female, the ovaries begin to form eggs.
The
fetus now has regular sleeping and waking patterns. They can also hear sounds
from outside the womb, and they will begin to practice swallowing, which is an
important skill after delivery.
The
woman will also likely begin to feel better. In most cases, morning sickness
and fatigue start
to go away at the beginning of the second trimester. Food cravings and
aversions can continue, however.
A
woman may notice that her belly is starting to grow and that she is beginning
to "look pregnant." She should also start to feel the
baby moving, which is called "quickening."
Braxton–Hicks
contractions may start toward the end of the second trimester.
A
woman may also begin to experience other symptoms in the second trimester,
including:
- round
ligament pain
- nipple
changes, such as darkening
- stretch
marks
The third trimester
The third trimester lasts from week 27 until delivery, which is
usually around week 40. During this trimester, a developing baby will grow from
around 12 inches long and 1.5 lbs in weight to about 18–20 inches long and 7–8
lbs in weight.
Most of the organs and body systems have formed by now, but they
will continue to grow and mature during the third trimester.
The fetus's lungs are not fully formed at the beginning of this
trimester, but they will be by the time of delivery.
A growing baby will start practicing breathing motions to help
prepare for life after birth. Kicks and rolls become stronger, and a pregnant
woman should feel the baby move regularly.
A pregnant woman may also begin to feel uncomfortable during
this trimester, as her belly starts to grow. Most women start to feel
Braxton–Hicks contractions getting stronger, and they may have back pain from carrying a heavy belly.
Other symptoms that a pregnant woman may experience during the
third trimester include:
- heartburn
- swollen feet
- insomnia
- mood swings
- leakage of
milk from the breasts
- other breast
and nipple changes
- frequent
urination
As the woman gets closer to the delivery, the baby should turn
in to a head-down position to make birth easier.
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