INTRODUTION
Conception is the time when
sperm travels up through the vagina, into the uterus, and fertilizes an egg
found in the fallopian tube. Conception — and ultimately, pregnancy — can
involve a surprisingly complicated series of steps. Everything must fall into
place for a pregnancy to be carried to term. Conception occurs during the part
of a woman’s menstrual cycle called ovulation. Doctors consider day 1 of a
menstrual cycle the first day of a woman’s period. Ovulation usually occurs
around the midpoint of a woman’s menstrual cycle. This would fall
around day 14 in a 28-day cycle, but it’s important to remember that even
normal cycle lengths can vary. During ovulation, one of the ovaries releases an
egg, which then travels down one of the fallopian tubes. If there’s sperm
present in a woman’s fallopian tube when this happens, the sperm could
fertilize the egg. Usually, an egg has about 12 to 24 hours where it can be
fertilized by sperm. However, sperm can live for several days in a woman’s
body. Therefore, when the ovary releases the egg, sperm that are already
present from intercourse a few days before could fertilize it. Or, if a woman
has sex during the time the egg has been released, the sperm could fertilize
the just-released egg.(
Bergman, 2006)
Conception
Conception
comes down to timing, the health of a woman’s reproductive tract, and the
quality of a man’s sperm. Most doctors usually recommend having unprotected sex
starting about three to six days before you ovulate, as well as the day you
ovulate if you wish to become pregnant. This increases the chances that sperm
will be present in the fallopian tube to fertilize the egg once it’s released.
Conception-related concerns
Conception
requires several steps to come together. First, a woman must release a healthy
egg. Some women have medical conditions that prevent them from ovulating altogether.
A
woman must also release an egg healthy enough for fertilization. A woman is
born with the number of eggs she will have throughout her lifetime. As she gets
older, the quality of her eggs diminishes.
This
is most true after age 35, according to the Royal College of Obstetricians and Gynecologists Trusted
Source.
High-quality
sperm are also required to reach and fertilize the egg. While only one sperm is
needed, the sperm must travel past the cervix and uterus into the fallopian
tubes to fertilize the egg. If a man’s sperm aren’t motile enough and can’t travel that
far, conception can’t occur. A woman’s cervix must also be receptive enough for
the sperm to survive there. Some conditions cause the sperm to die before they
can swim to the fallopian tubes. Some women may benefit from assisted
reproductive technologies like intrauterine insemination or in vitro fertilization if there are
issues preventing healthy sperm from meeting a healthy egg naturally.
Stages of Growth
Month-by-Month in Pregnancy
First trimester
The
first trimester will span from conception to 12 weeks. This is generally the
first three months of pregnancy. During this trimester, the fertilized egg will
change from a small grouping of cells to a fetus that is starting to have a
baby’s features.
Month 1 (weeks 1 through 4)
As
the fertilized egg grows, a water-tight sac forms around it, gradually filling
with fluid. This is called the amniotic sac, and it helps cushion the growing
embryo.
During
this time, the placenta also develops. The placenta is a round, flat organ that
transfers nutrients from the mother to the fetus, and transfers wastes from the
fetus. Think of the placenta as a food source for the fetus throughout your
pregnancy. In these first few weeks, a primitive face will take form with large
dark circles for eyes. The mouth, lower jaw and throat are developing. Blood
cells are taking shape, and circulation will begin. The tiny "heart"
tube will beat 65 times a minute by the end of the fourth week. By the end of
the first month, the fetus is about 1/4 inch long – smaller than a grain of
rice.
Month 2 (weeks 5 through 8)
Facial
features continue to develop. Each ear begins as a little fold of skin at the
side of the head. Tiny buds that eventually grow into arms and legs are
forming. Fingers, toes and eyes are also forming. The neural tube (brain,
spinal cord and other neural tissue of the central nervous system) is well
formed now. The digestive tract and sensory organs begin to develop too. Bone
starts to replace cartilage.
The
head is large in proportion to the rest of the body at this point. At about 6
weeks, a heartbeat can usually be detected. After the 8th week, healthcare
providers refer to it as a fetus instead of an embryo. By the end of the second
month, the fetus is about 1 inch long and weighs about 1/30 of an ounce.
Month 3 (weeks 9 through 12)
The
arms, hands, fingers, feet and toes are fully formed. At this stage, the fetus
is starting to explore a bit by doing things like opening and closing its fists
and mouth. Fingernails and toenails are beginning to develop and the external
ears are formed. The beginnings of teeth are forming under the gums. The
reproductive organs also develop, but gender is still difficult to distinguish
on ultrasound.
By
the end of the third month, the fetus is fully formed. All the organs and limbs
(extremities) are present and will continue to develop in order to become
functional. The circulatory and urinary systems are also working and the liver
produces bile. At the end of the third month, the fetus is about 4 inches long
and weighs about 1 ounce. Since the most critical development has taken place,
your chance of miscarriage drops
considerably after three months.
Second trimester
This
middle section of pregnancy is often thought of as the best part of the
experience. By this time, any morning sickness is probably gone and the
discomfort of early pregnancy has faded. The fetus will start to develop facial
features during this month. You may also start to feel movement as the fetus
flips and turns in the uterus. During this trimester, many people find out
whether their baby will be designated male or female at birth. This is
typically done during an anatomy scan (an ultrasound that checks physical
development) around 20 weeks.
Month 4 (weeks 13 through 16)
The
fetal heartbeat may now be audible through an instrument called a doppler. The
fingers and toes are well-defined. Eyelids, eyebrows, eyelashes, nails and hair
are formed. Teeth and bones become denser. The fetus can even suck his or her
thumb, yawn, stretch and make faces. The nervous system is starting to
function. The reproductive organs and genitalia are now fully developed, and
your doctor can see on ultrasound if the fetus will
be designated male or female at birth. By the end of the fourth month, the
fetus is about 6 inches long and weighs about 4 ounces.
Month 5 (weeks 17 through 20)
At
this stage, you may begin to feel the fetus moving around. The fetus is
developing muscles and exercising them. This first movement is called
quickening and can feel like a flutter. Hair begins to grow on the head. The
shoulders, back and temples are covered by a soft fine hair called lanugo. This
hair protects the fetus and is usually shed at the end of your baby's first
week of life. The skin is covered with a whitish coating called vernix caseosa.
This "cheesy" substance is thought to protect fetal skin from the
long exposure to the amniotic fluid. This coating is shed just before birth. By
the end of the fifth month, the fetus is about 10 inches long and weighs from
1/2 to 1 pound.
Month 6 (weeks 21 through 24)
If
you could look inside the uterus right now, you would see that the fetus's skin
is reddish in color, wrinkled and veins are visible through translucent skin.
The finger and toe prints are visible. In this stage, the eyelids begin to part
and the eyes open.
The
fetus responds to sounds by moving or increasing the pulse. You may notice
jerking motions if the fetus hiccups. If born prematurely, your baby may survive
after the 23rd week with intensive care. By the end of the sixth month, the
fetus is about 12 inches long and weighs about 2 pounds.
Month 7 (weeks 25 through 28)
The
fetus continues to mature and develop reserves of body fat. At this point,
hearing is fully developed. The fetus changes position frequently and responds
to stimuli, including sound, pain and light. The amniotic fluid begins to
diminish. If born prematurely, your baby would be likely to survive after the
seventh month.
At
the end of the seventh month, the fetus is about 14 inches long and weighs from
2 to 4 pounds.
Third Trimester
This
is the final part of your pregnancy. You may be tempted to start the countdown
till your due date and hope that it would come early, but each week of this
final stage of development helps the fetus prepare for birth. Throughout the
third trimester, the fetus gains weight quickly, adding body fat that will help
after birth. Remember, even though popular culture only mentions nine months of
pregnancy, you may actually be pregnant for 10 months. The typical, full-term
pregnancy is 40 weeks, which can take you into a tenth month. It’s also
possible that you can go past your due date by a week or two (41 or 42 weeks).
Your healthcare provider will monitor you closely as you approach your due
date. If you pass your due date, and don’t go into spontaneous labor, your
provider may induce you. This means that medications will be used to make you
go into labor and have the baby. Make sure to talk to your healthcare provider
during this trimester about your birth plan.
Month 8 (weeks 29 through 32)
The
fetus continues to mature and develop reserves of body fat. You may notice more
kicking. The brain developing rapidly at this time, and the fetus can see and
hear. Most internal systems are well developed, but the lungs may still be
immature. The fetus is about 18 inches long and weighs as much as 5 pounds.
Month 9 (weeks 33 through 36)
During
this stage, the fetus continues to grow and mature. The lungs are close to
being fully developed at this point. The fetus has coordinated reflexes and can
blink, close the eyes, turn the head, grasp firmly, and respond to sounds,
light and touch. The fetus is about 17 to 19 inches long and weighs from 5 ½
pounds to 6 ½ pounds.
Month 10 (Weeks 37 through 40)
In
this final month, you could go into labor at any time. You may notice
that less movement because space is tight. At this point, The fetus's position
may have changed to prepare for birth. Ideally, it's head down in your uterus.
You may feel very uncomfortable in this final stretch of time as the fetus
drops down into your pelvis and prepares for birth. Your baby is ready to meet
the world at this point. They are about 18 to 20 inches long and weigh about 7
pounds.
CONCEPTION DEVELOPMENT FROM EGG TO EMBRYO
Conception: From Egg to Embryo
This
slideshow will illustrate the incredible process of conception, beginning with
the moment a sperm fertilizes an egg.
Ovulation
Each
month, one of a woman's two ovaries releases a mature egg in a process known
as ovulation. Ovulation occurs about two weeks
after the start of a woman's last menstrual period.
Moving Into the Fallopian Tube
The
released egg travels into the Fallopian tube, where it is fertilized by a
single sperm.
The Sperm's Long Journey
When
a man ejaculates, 40 to 150 million sperm may be contained in the fluid. The
sperm start swimming upstream in the women's reproductive tract toward the
Fallopian tubes. The time it takes for sperm to reach an egg is very variable -
some may reach their target in half an hour, while others may take days. Sperm
can live for up to 48 to 72 hours. Of the millions of sperm, only a few hundred
even come close to the egg.
Fertilization: Sperm Penetrates Egg
The
process of fertilization takes about 24
hours. Once a sperm has penetrated the egg, the egg surface changes, preventing
entry of other sperm. Fertilization completes the genetic makeup of the baby,
including whether it will be a girl or boy.
The Cells Start to Divide
Once
the egg is fertilized, a rapid process of division begins. The fertilized egg
leaves the Fallopian tube and enters the uterus 3 to 4 days after
fertilization. A tubal or ectopic pregnancy results in the rare cases in which
the fertilized egg does not properly enter the uterus. An ectopic pregnancy
poses serious health risks to the mother.
Implantation
Implantation
is the process by which the fertilized egg attaches to the endometrium (lining
tissues of the uterus). The cells in the fertilized egg continue to divide.
Pregnancy Hormones
A
hormone called human chorionic gonadotrophin (HCG) is produced by the cells
that will eventually form the placenta. It can be found in the mother's blood
within about a week of conception and is detected in pregnancy tests done on
blood or urine.
Fetal Development
After
implantation in the uterus, some of the cells form the placenta while others
form the embryo. The heartbeat begins during the fifth week of gestation. At
the eighth week the developing embryo is now called a fetus. The fetus at eight
weeks is about ½ inch long and constantly growing.
FACTORS
AFFECTING CONCETION DEVELOPMENT
Factors
influencing development
Poverty
Poverty has been linked to poor
prenatal care and has been an influence on prenatal development. Women in
poverty are more likely to have children at a younger age, which results in low
birth weight. Many of these expecting mothers have little education and are
therefore less aware of the risks of smoking, drinking alcohol, and drug
use – other
factors that influence the growth rate of a fetus.
Mother's age
Women between the ages of 16 and 35
have a healthier environment for a fetus than women under 16 or over 35, Women
between this age gap are more likely to have fewer complications. Women over 35
are more inclined to have a longer labor period, which could potentially result
in death of the mother or fetus. Women under 16 and over 35 have a higher risk
of preterm labor (premature baby), and this risk increases for women in
poverty, women who take drugs, and women who smoke. Young mothers are more
likely to engage in high risk behaviors, such as using alcohol, drugs, or
smoking, resulting in negative consequences for the fetus. Premature
babies from young mothers are more likely to have neurological defects that
will influence their coping capabilities – irritability, trouble sleeping,
constant crying for example. There is an increased risk of Down syndrome for infants born to those aged
over 40 years. Young teenaged mothers (younger than 16) and mothers over 35 are
more exposed to the risks of miscarriages, premature births, and birth defects.
Drug use
An estimated 5 percent of fetuses in
the United States are exposed to illicit drug use during
pregnancy. Maternal drug use occurs when drugs ingested by the pregnant
woman are metabolized in the placenta and then transmitted to the fetus. Resent
research display that there is a correlation between fine motor skills and
prenatal risk factors such as the use of psychoactive substances and signs of
abortion during pregnancy. As well as perinatal risk factors such as gestation
time, duration of delivery, birth weight and postnatal risk factors such as
constant falls.
Cannabis
When using cannabis, there is a greater risk of birth
defects, low birth weight, and a higher rate of death in infants or
stillbirths. Drug use will influence extreme irritability, crying, and
risk for SIDS once the fetus is born. Marijuana will slow the fetal growth rate
and can result in premature delivery. It can also lead to low birth weight, a
shortened gestational period and complications in delivery. Cannabis use during pregnancy
was unrelated to risk of perinatal death or need for special care, but, the
babies of women who used cannabis at least once per week before and throughout
pregnancy were 216g lighter than those of non‐users, had significantly shorter
birth lengths and smaller head circumferences.[34]
Cocaine
Cocaine use results in a smaller
brain, which results in learning disabilities for the fetus. Cocaine puts the
fetus at a higher risk of being stillborn or premature. Cocaine use also
results in low birthweight, damage to the central nervous system, and motor
dysfunction. The vasoconstriction of the effects of cocaine lead to a decrease
in placental blood flow to the fetus that results in fetal hypoxia that is
oxygen deficiency and decreased fetal nutrition these vasoconstrictive effects
on the placenta have been linked to the number of complications in
malformations that are evident in the newborn.
Alcohol
Maternal alcohol use leads to
disruptions of the fetus's brain development, interferes with the fetus's cell
development and organization, and affects the maturation of the central nervous
system. Even small amounts of alcohol use can cause lower height, weight and
head size at birth and higher aggressiveness and lower intelligence during
childhood. Fetal alcohol spectrum disorder is a developmental disorder
that is a consequence of heavy alcohol intake by the mother during pregnancy.
Children with FASD have a variety of distinctive facial features, heart
problems, and cognitive problems such as developmental disabilities, attention
difficulties, and memory deficits.
Tobacco use
Tobacco smoking during pregnancy exposes the
fetus to nicotine, tar, and carbon monoxide. Nicotine results in less blood flow
to the fetus because it constricts the blood vessels. Carbon monoxide reduces
the oxygen flow to the fetus. The reduction of blood and oxygen flow may result
in miscarriage, stillbirth, low birth weight, and premature births. Exposure to
secondhand smoke leads to higher risks of low birth weight and childhood
cancer.
Infections
If a mother is infected with a disease, the placenta
cannot always filter out the pathogens. Viruses such as rubella, chicken pox, mumps, herpes, and human immunodeficiency virus (HIV) are associated with an
increased risk of miscarriage, low birth weight, prematurity, physical malformations, and intellectual disabilities. HIV
can lead to acquired immune deficiency syndrome (AIDS). Untreated HIV carries a
risk of between 10 and 20 per cent of being passed on to the fetus. Bacterial or parasitic
diseases may also be passed on to the fetus, and include chlamydia, syphilis, tuberculosis, malaria, and commonly toxoplasmosis. Toxoplasmosis can be acquired
through eating infected undercooked meat or contaminated food, and by drinking
contaminated water. The risk of fetal infection is lowest during early
pregnancy, and highest during the third trimester. However, in early pregnancy
the outcome is worse, and can be fatal.[44]
Maternal
nutrition
Adequate nutrition is needed for a
healthy fetus. Mothers who gain less than 20 pounds during pregnancy are at
increased risk for having a preterm or low birth weight infant. Iron and iodine
are especially important during prenatal development. Mothers who are deficient
in iron are at risk for having a preterm or low birth weight
infant. Iodine deficiencies increase the risk of miscarriage, stillbirth,
and fetal brain abnormalities Adequate prenatal care gives an improved result in
the newborn.
Stress
Stress during pregnancy can impact
the development of the embryo. Reilly (2017) states that stress can come from
many forms of life events such as community, family, financial issues, and
natural causes. While a woman is pregnant, stress from outside sources can take
a toll on the growth in the womb that may affect the child's learning and
relationships when born. For instance, they may have behavioral problems and
might be antisocial. The stress that the mother experiences affects the fetus
and the fetus' growth which can include the fetus' nervous system (Reilly,
2017). Stress can also lead to low birth weight. Even after avoiding other
factors like alcohol, drugs, and being healthy, stress can have its impacts
whether families know it or not. Many women who deal with maternal stress do
not seek treatment. Similar to stress, Reilly stated that in recent studies,
researchers have found that pregnant women who show depressive symptoms are not
as attached and bonded to their child while it is in the womb (2017).
Environmental
toxins
Exposure to environmental toxins in pregnancy lead to higher rates of
miscarriage, sterility, and birth defects. Toxins include fetal exposure to
lead, mercury, and ethanol or hazardous environments. Prenatal exposure to
mercury may lead to physical deformation, difficulty in chewing and swallowing,
and poor motoric coordination. Exposure to high levels of lead prenatally
is related to prematurity, low birth weight, brain damage, and a variety of
physical defects. Exposure to persistent air pollution from traffic and smog may lead to reduced infant head size, low birth weight,
increased infant death rates, impaired lung and immune system development.
CONCLUSION
At
conception the egg and sperm cell are united to form a zygote, which will begin
to divide rapidly. This marks the beginning of the first stage of prenatal
development (germinal stage), which lasts about two weeks. Then the zygote
implants itself into the lining of the woman’s uterus, marking the beginning of
the second stage of prenatal development (embryonic stage), which lasts about
six weeks. The embryo begins to develop body and organ structures, and the neural
tube forms, which will later become the brain and spinal cord. The third phase
of prenatal development (fetal stage) begins at 9 weeks and lasts until birth.
The body, brain, and organs grow rapidly during this stage. During all stages
of pregnancy it is important that the mother receive prenatal care to reduce
health risks to herself and to her developing baby. (Svenonius, 2000))
REFERENCE
Elaine
Svenonius, (2000). The Intellectual
Foundation of Information Organization, MIT Press, 2000, 255pp.
I’d like to thank Karen Coyle for recently posting this quote on the Linked
Library Data (LLD) mailing
list.
Marcia Lei Zeng, Maja
Žumer, Athena Salaba, eds., (2010). Functional Requirements for
Subject Authority Data (FRSAD): A Conceptual Model, prepared by the
IFLA Working Group on the Functional Requirements for Subject Authority Records
(FRSAR), June 2010, 75 pp. See http://www.ifla.org/files/classification-and-indexing/functional-requirements-for-subject-authority-data/frsad-final-report.pdf. This effort is part of the broader and well-known FRBR
(Functional Requirements of Bibliographic Records) initiative.
Melissa
Conrad Stöppler, MD on 1/15/2021
See M. K. Bergman, 2006. “Sources and Classification of
Semantic Heterogeneities,” AI3:::Adaptive Information blog,
June 6, 2006. See https://www.mkbergman.com/232/sources-and-classification-of-semantic-heterogeneities/.
See M. K. Bergman, 2010. “The Nature of
Connectedness on the Web,” AI3:::Adaptive Information blog,
November 22, 2010. See https://www.mkbergman.com/935/the-nature-of-connectedness-on-the-web/.
