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The Miracle of Life
Sperm Meets Egg, Fertilization, Conception,
Gestation and Birth
The length of a pregnancy is traditionally calculated
to be 10 months (40 weeks) from the first day of the last period
before conception until birth. Since the last period usually begins
14 days before ovulation, the actual time from fertilization until
birth is more like 9 1/2 months (38 weeks). In this section we describe
the age of a developing baby as starting the moment fertilization
occurs.
The First Trimester
Fertilization
Ejaculation by the male sends hundreds of millions
of sperm on a swimming frenzy into the vagina. The strong and healthy
sperm proceed on a 2 to 7 hour journey through the cervix into the
uterus and into the fallopian tubes. Several hundred are able to
make it to the egg floating through the fallopian tube. Sperm can
survive and remain capable of fertilizing an egg for up to 72 hours
or longer. When the hundreds of strong sperm reach the egg they
surround it and together clear a path through its outer covering
(the zona pellucida) enabling one lucky sperm to penetrate the egg
completely, losing his tail in the process. As soon as this occurs
a protective layer is immediately formed to prevent any other sperm
from penetrating the egg. All the sperm's comrades are then
sacrificed in the name of manhood! The nucleus of the sperm joins
the nucleus of the egg combining the chromosomes from the two parents
into one nucleus. At this point the egg has become a zygote and
all genetic characteristics from eye color to disposition have been
determined.
Conception
0 hours: Starting
at the moment of fertilization, the zygote (fertilized egg) begins
its journey toward the wall of the uterus while beginning to grow
by cell division.
36
hours: The first cell division is complete (the zygote
has now graduated to a two-cell conceptus, or pre-embryo.
2
days (48 hours): Both cells have divided again. Cell divisions
take place about every 12 hours from that time on.
3
days (72 hours): after fertilization the conceptus
has gained the right to be called a morula by forming into a 16-cell
mass.
5
days: The conceptus arrives in the uterus. It has now attained
the title, blastocyst, and consists of a hollow sphere of cells
with a small cluster of cells on one side. The inner cells of the
blastocyst will form into the embryo, while the outer cells of the
blastocyst will form part of the placenta, which will nourish and
supply oxygen to the developing baby.
7
days:
The conceptus burrows into the inner lining of the uterus, thus
implantation has occurred and conception is now complete.
Gestation
6 weeks:
The tiny embryo no larger than 1/4 of an inch is floating in a protective
sac. Its nervous, circulatory and digestive systems are developing.
A rudimentary brain, ears, eyes and mouth have appeared. Its heart
is beating. Four limb-buds, the precursors to arms and legs, have
appeared. Its umbilical cord connects it to the placenta, where
the blood of the mother and that of the baby come close enough to
transfer nutrients and oxygen.
The embryo
sends hormonal message to the corpus luteum gland in the ovaries
causing it to continue producing hormones that sustain the nutrient
rich environment in the lining of the uterus, thus preventing a
period from occurring.
2
months
(8 weeks):
The 1.25-inch embryo's internal organs have formed. The arms,
elbows, legs and knees are well defined with fingers and toes in
the process of formation. The ears and mouth are forming.
After 8 weeks, the developing baby is known as a
fetus.
3
months
(12 weeks): The fetus has grown
to become 3 inches long. The ears and eyelids have formed. The fetus
can open and close its mouth and even suck its thumb, which along
with its fingers and toes is completely formed. The limbs move.
The external genitals have formed. The mother can hear her child's
heartbeat through an amplifier. Morning sickness dissipates.
The Second Trimester
13 weeks: All internal
organs, tissues, limbs and external features have formed. This marks
the beginning of the seecond trimester.
4
months
(16 weeks):
The mother may appear to be pregnant.
The sex of the 6-inch fetus can be determined by a sonogram or ultrasound.
The bones are developing and the muscles are gaining strength.
5
months
(20 weeks):
Hair grows on the head of the 10-inch fetus and fine hair appears
on the body. The condition of the mother's hair and skin improves.
The mother can feel the fetus moving and kicking.
6
months
(24 weeks):
The fetus is 13 inches and growing rapidly.
The Third Trimester
26
weeks: This marks the beginning of the
third trimester.
7 months
(28 weeks):
The baby has grown to 14 1/2 inches. The brain developes rapidly.
The baby has a good chance to survive a premature birth at this
point.
8
months
(32 weeks):
The 16-inch fetus is gaining fat under the skin. The mother feels
breathless. The baby may invert itself so its head is pointed toward
the cervix.
35
weeks:
If this is the mother's first pregnancy she can expect a shift in
the baby's positioning, called lightening or dropping, to occurr
during the last few weeks of pregnancy. If this is not the mother's
first baby, lightening probably won't ocurr until labor begins.
During lightening, the baby's body becomes inverted
and the head descends into the pelvis usully just behind the pubic
bone. The baby's body along with the curve of your abdomen shifts
down and forward. As a result, pressure is taken off the mother's
diaphragm making it easier for her to breath and to digest. This
gives the mother a lightened feeling. Thus the name "lightening."Although
pressure is relieved from the upper regions of the mothers abdomen,
increased pressure is applied within the pelvis. This can cause
a more frequent need to urinate, and aches and twinges of pain within
the pelvic region.
9
months
(36 weeks):
The 18-inch fetus is more round and plump as it stores up fat.
10
months (40 weeks, give or take a couple weeks): The 20-inch
fetus is full grown. The baby is born.
Birth
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