Pregnancy is generally
divided into trimesters. Your first trimester of pregnancy ends at
about twelve weeks, or three months after your last menstrual period.
Your doctor can discuss your progress in a few weeks, which are measured starting from the first day of your last menstrual day of period it your uses of doctor to calculate your expiry and the age gestationnel of the baby. Since it is usually impossible to indicate exactly the exact date of ovulation and the date of the design, the medical experts employ your last menstrual period like starting point during your nine following months. Basically, this means that the first week of your pregnancy is really the week that you began your last period. Therefore, your baby can be up to two weeks younger
than his gestational age. Every baby develops differently and at
different rates in utero.
The First Month (1 to 4 Weeks)
Approximately during two weeks after the first day of your last menstrual period, your ovary discharged an egg in the Fallopian tube. Your actual pregnancy began when that egg was
fertilized by a sperm cell. In other words, you are not actually
pregnant for the entire first month of pregnancy—weeks one through four.
Over the next week, the fertilized
egg grows into a group of cells called a blastocyst. Once the
blastocyst completes its journey down the fallopian tube, it implants
in the uterus and divides into two parts. One half of the blastocyst
attaches to the wall of the uterus and becomes the placenta while the
other half develops into the embryo. This group of cells is already
composed of different layers. The outer layer eventually becomes the
nervous system, skin, and hair. The middle layer becomes bones,
cartilage, muscles, circulatory system, kidneys, and sex organs. The
inner layer becomes the respiratory and digestive organs.
The implantation of the
egg into the uterus triggers the beginning of hormonal and physical
changes. The amniotic sac, which cushions the fetus in the months
ahead, begins to form. The early stages of the placenta and umbilical
cord are visible and under rapid construction.
During the first month of
pregnancy, the embryo looks like a tadpole. The neural tube, which will
become the brain and spinal cord, starts to come together. A very
primitive face begins to form, with large dark circles where the eyes
will be. The mouth, lower jaw, and throat also begin to develop. The
baby’s blood cells are taking shape, and circulation will soon begin.
By the end of the first month, the embryo is about a quarter of an inch
long and is smaller than a grain of rice.
The placenta is the interface
that provides all the nutrients the baby needs, including oxygen, and
takes care of waste disposal. It also produces the hormones
progesterone and estriol, which are produced to help maintain a healthy
pregnancy. The placenta develops in the uterus just twelve days after
conception.
The Second Month (5 to 8 Weeks)
You may not look pregnant yet, but
by the second month of your pregnancy, plenty is going on. Major body
organs are beginning to develop, including the heart, brain, kidneys,
liver, intestines, appendix, lungs, and body systems. The baby’s facial
features continue to develop. The baby’s ears, fingers, toes, and eyes
begin to form. Tiny buds that will become the baby’s arms and legs are
forming. The digestive tract and sensory organs are now beginning to
develop.
During this time, bone starts to
replace cartilage. The baby’s heart starts its contractions, which will
become distinct heartbeats within the next week. The eyelids form and
grow—though sealed shut—and nostrils begin to form.
The neural tube will eventually
connect the brain and spinal cord, and by about the fifth week it
closes. Blood circulation becomes evident at this time. The placenta
and amniotic sac continue to develop. By the end of the second month,
the embryo has started to look more like a person than a tadpole. It
measures about 1 inch long and weighs less than 
ounce.
The Third Month (9 to 12 Weeks)
During your third month of
pregnancy, the embryo has developed into a fetus. The baby is active,
even though you may not yet be able to feel the activity. All major
organs, muscles, and nerves are formed. The mouth has twenty buds that
will eventually become teeth. The irises of the eyes are now forming.
The liver, intestines, brain, and lungs are now beginning to function
on their own. At around week eleven, it is possible to hear the
“swooshing” sound of the baby’s heartbeat for the first time with a
special instrument called a Doppler sound-wave stethoscope.
A Doppler stethoscope uses
ultrasound to listen to the heartbeat of the fetus. The device is
sometimes called a Doptone. The Doppler may be routinely used during
your prenatal visits.
Several of the baby’s ribs are now
visible, and tissue that will eventually form bones is developing
around the baby’s head, arms, and legs. By the end of your first
trimester, or third month, your baby is fully formed. Your little one
has arms, hands, fingers, feet, and toes. Fingers and toes are
separate, and they now have soft nails. Your baby’s reproductive organs
are developing, and the circulatory and urinary systems are working.
The liver is producing bile.
Throughout the remainder
of your pregnancy, the baby’s body organs will mature and the fetus
will gain weight, become longer, and fully develop. By the end of your
third month, your baby is about four inches in length and weighs about
1 ounce. The most critical point of formation of the organs is
finished, and your chance of miscarriage at this point drops
considerably.
