general facts about pregnancy pregnancy lasts for 266 days on average. doctors count first day...

General facts about pregnancy

Pregnancy lasts for 266 days on average. Doctors count first day last menstrual

period (LMP)—not the day you conceive--as the first day of pregnancy

According to the medical model, pregnancy lasts 40 weeks; it’s actually 38 weeks from the time of conception until birth (on average).

Three distinct periods of development

Period of the zygote (weeks 1-2)-also called the germinal period

Period of the embryo (weeks 3-8) Period of the fetus (weeks 9-38) **These are not the same as first,

second, and third trimester

Period of the zygote (germinal period)

First two weeks after conception Period of rapid development Zygote becomes the blastocyst--hollow

inner layer of cells, which implants into the uterine lining on days 7-9

Trophoblast—outer layer of cells; becomes the placenta

Differentiation of cells begin 30-50% of conceptions don’t make it

through this period Placenta is formed at the end of this stage

Life support systems of the embryo

Amnion—sac filled with clear fluid in which embryo floats

Placenta—disk-shaped group of tissues that allows food and oxygen to reach the embryo; carries waste products away

Umbilical cord—contains two arteries and one vein that connect the baby to the placenta.

Embryo’s and mom’s blood supplies come in close contact but never mix directly

Placenta at around 8 weeks

Placenta at birth

The placenta is the baby’s life support system throughout pregnancy.

Developmental trends

Cephalocaudal—from head to tail; development occurs head-down

Head region accounts for 50% of total length during the first month

Proximodistal—development occurs “from the inside out”—midline outward

Same pattern of development throughout childhood

Period of the embryo

Dramatic and rapid growth takes place Groundwork for all body structures and

internal organs is laid By the end of this period, all of the

structures and internal organs a baby is born with are already formed

By the end of this period, embryo loses its gills and tail and looks more human.

Cellular differentiation in the embryo Three distinct layers are formed:

Ectoderm: outer layer of the embryo—gives rise to the nervous system, skin, hair, teeth, nails, and teeth

Mesoderm: middle layer—gives rise to muscles, skeleton, circulatory, and excretory systems

Endoderm: inner layer which gives rise to the respiratory system, liver, and pancrease

Organogenesis during the first four weeks

The process of organ formation 3rd week: neural tube forms (becomes

spinal cord) 21 days—eyes appear 24 days—heart cells begin to differentiate 4th week—urogenital system is apparent;

arm & leg buds emerge Primitive mouth, intestinal tract, liver form Primitive brain forms Embryo is 1/6 of an inch long

The embryo at 6 weeks

Neural Induction

The process of beginning the development of the nervous system at the start of the third week

Starts with a chemical signal from the mesoderm to the ectoderm, causing a portion of the ectoderm to become the neural plate

Nervous System Development Begins with neural induction of the neural

plate Neural tube then forms; top becomes the

brain and the rest becomes the spinal cord.

Even in the early days of neural tube development, neurons know to what part of the brain they’ll travel and what time of nerve cell they’ll become (motor, vision, hearing, etc.)

Speed of Neural Development Cell proliferation: nerve cells begin to form

in the neural tube at a rate of 250,000 per minute for the entire pregnancy. 30,000 synapses are formed every second. Baby is born with 100 billion neurons.

Cell migration: begins during 7th week; neurons begin their destination in the developing brain.

Some neurons travel distances equal to the distance between Boston and San Francisco!

1000 trillion connections in the brain begin to form, followed by a pruning process that continues throughout life.

Embryonic development at 8 weeks

Embryo is 1 ½ inches long and 1 oz. In weight

Arm and leg differentiate further Elaborate peripheral nervous system in place Glandular system operating Internal sex organs developed (NOTE: Sex is

determined at conception.) Embryo can move, but movements can’t be

felt by mom yet. 95% of body parts are differentiated (arms,

legs, beating heart, nervous system, etc.) by the 8th week.

8-week-old embryo

Early Period of the fetus (weeks 9-12)

Embryo becomes a fetus when bone replaces cartilage

Facial features become distinct, human-like Vocal cords, nails, lungs have formed External genitalia are identifiable Heartbeat can be heard Baby can urinate Baby can smile, frown, suck, and swallow About 3 inches long; weighs about 1 ounce

Middle months of period of the fetus (5th-6th month)

12-15 inches long, 12-32 ounces Grasping reflex; baby sucks thumb Lung breathing is possible Sleep/wake cycles similar to newborn’s Eyes and ears are sensitive to light and

sound; visibility is obtained. Very sensitive to touch All neurons present by 24 weeks’ gestation Rapid growth during 6th month; slows during

7th month.

Vernix and lanugo

Appear in 5th-6th month Vernix—cheeselike covering to protect

skin from chapping Lanugo—white, downy hair on body to

protect skin from chapping

Fetus with vernix and lanugo Vernix and lanugo are often still present

at birth, especially if the baby is preterm.

Age of viability

This is the age by which the fetus can survive outside the womb

Usually this is between 22-26 weeks’ gestation

By the 24th week, the fetus has a 50% chance of survival.

Fetal Development by Month 3rd month: sex organs appear. Visible by 12

weeks. 4th month: rapid growth; red blood cells

develop; active sucking reflex 5th month: hears sound, sleeps, 10-12 oz.

long, 1 pound 6th month: rapid growth, 12-14 inches, 2

pounds 7th month: growth slows; viability attained 8th and 9th month: baby plumps up, senses

ready to function, brain is 25% of adult weight

Last months (7-9) of pregnancy

Lungs gradually mature Rapid brain development causes sensory &

behavioral capacities to expand Antibodies are transferred from mom to

baby Baby becomes better able to regulate

temperature Gains 3.5 pounds in fat Engagement (baby’s head in birth canal) by

36 weeks Baby weighs on average 7 ½ pounds at birth

Ethical Issues during Pregnancy Embryonic adoption…what to do with frozen

embryos that the biological parents do not want

Stem cell research Embryonic stem cells are those cells that have

been removed from the inner cell mass of the blastocyst about 4 days after conception.

These cells are called pluripotent cells, which are capable of becoming almost any cell in the human body until they begin to specialize. If left alone, the pluripotent cells develop into a viable embryo.

Sex Differences in Utero

Males are more physically active—they remain more active through childhood

Females are more sensitive to external stimulation

Females advance more rapidly in skeletal development and are 1-2 weeks ahead of males in bone development at birth. Trait remains through early adolescence.

More boys are conceived than girls, but the birth rate is roughly equal (105 males to 100 females)

Mozart effect

The finding that exposing fetuses and babies to classical music (specifically Mozart) is associated with greater math and spatial ability test scores.

The finding has been disputed recently. Seems to increase math skills in adults for about 30 minutes after listening to it.

Sounds and tastes infants prefer

They prefer their mother’s voice over all others

No preference in father’s voice over other men’s

Fetuses develop taste preferences and aversions; strong tastes such as garlic are present in the amniotic fluid (also in breast milk)

Fetal tastes may influence later taste preferences.

Habituation

Getting accustomed to a certain stimulus in the womb

Fetuses at 26 weeks of age show habituation to repeated stimuli

Some psychologists think that how quickly a fetus habituates to a routine stimulus predicts future intelligence. This is debatable.

Teratogens

Any environmental agent that can interfere with the process of normal growth (even vitamins can be teratogens)

Especially harmful in the embryonic stage because this is when organs are being formed.

Effects of a teratogenic substance are worse on the body part or organ systems that are being formed at the time of exposure

Does a teratogen always cause damage?

No—a specific teratogen usually does NOT cause a specific birth defect.

Three factors influence the effects of a teratogen: Dose—the greater the dose, the greater the

effect. Genetic susceptibility—both the mother’s and

baby’s genotypes influence vulnerability. Timing—Teratogens do more damage at

specific times of development.

Times of greatest vulnerability when exposed to teratogens

Brain: 15 to 25 days after conceptionEyes: 24-40 days after conceptionHeart: 20 to 40 days after conceptionLegs: 24-37 days*Each body part has its own critical time of

formation. Only about half of all potential effects of a

teratogen are evident at birth.

Why are teratogens harmful to baby but not to Mom?

Mother weighs a lot more Mother’s organs aren’t developing like

the baby’s are The placenta and immature fetal liver

may be unable to convert a harmful substance to a harmless one

STORCH

Refers to the following infectious diseases that are teratogens Syphilis (50% die; blindness, retardation, deafness) Toxoplasmosis (protozoan virus transmitted by cats;

neurological problems, preterm delivery, or miscarriage)

Other infections (flu, chicken pox, measles, etc.) Rubella (German measles; blindness, deafness,

retardation, death) Cytomegalovirus (CMV..no treatment for this…casus

retardation, blindness, deafness, possibly death) Herpes (Herpes II is the genital kind; contracted in

birth canal; child develops symptoms in 1st week of life. Affects CNS.)

Examples of teratogens

Over-the-counter, prescription, and illegal drugs

Caffeine—medical opinions differ as to whether it’s harmful or not (4 cups or more of coffee a day is considered harmful)

Tobacco—associated with low birth weight, miscarriage, SIDS, asthma, and childhood cancer

Alcohol—can result in fetal alcohol syndrome Maternal malnutrition—smaller brain size Maternal stress—associated with

miscarriage, preterm labor, low birth weight

Fetal alcohol syndrome

Involves mental retardation, impaired motor coordination, poor attention and memory, and certain physical characteristics.

Heroin

Well-documented effects: behavioral disturbances in children of heroin-addicted mothers

Infants have tremors, show irritability, abnormal crying, sleep disturbances, and impaired motor control.

These are all symptoms of heroin withdrawal.

Many still have behavioral problems at 1 year old, and studies show attention deficits later in development.

Methamphetamine (meth)

Babies are at significant risk of infant mortality, low birth weight, and developmental and behavioral problems.

Respiratory difficulties, neurological problems, poor cognitive functioning, and abuse and neglect by parents are common.

Meth use during pregnancy is increasing and is now considered an even greater problem than cocaine use.

What about fish?

Some fish, especially large fish such as tuna, sharks, swordfish, etc., contain high levels of mercury.

Mercury crosses the placenta easily and leaves the infant highly sensitive to brain and nervous system defects.

FDA in 2004 advised women of childbearing age and young children not to eat shark, swordfish, king mackerel or tilefish. They can eat up to 12 ounces (2 meals) a week of shrimp, canned light tuna, salmon, pollock, & catfish.

Maternal Age

Considered a teratogen Over age 35, problems increase

dramatically (more trouble getting pregnant, risk of birth defects & chromosomal problems)

Teenage mothers show the same problems as older mothers, especially in rates of Down’s syndrome

What about paternal age?

Older fathers have children who face increased risk of certain birth defects, including Down syndrome, dwarfism, Marfan syndrome (involves head & limb deformities), and perhaps autism.

When both parents are older (mom over 35; dad over 40), the risk of miscarriage is greater.

Genital herpes

Newborns contract genital herpes when they pass through the birth canal of an infected mother.

About 1/3 of the babies die, and another ¼ are brain damaged if delivered by a mother with active herpes.

A C-section may be performed if mother has an active case of herpes near the time of delivery.

AIDS

Mothers can transmit HIV to their infants in one of 3 ways: Across the placenta During delivery through contact with maternal

blood/fluids Postpartum through breastfeeding Infants can be infected but asymptomatic; they

can still develop symptoms up to 15 months old. Risk is reduced by giving pregnant HIV-infected

moms AZT during pregnancy and the baby AZT after birth; a “bloodless” C-section can also help.

An infected mother will pass HIV along 30-50% of the time

AIDS in babies

AIDS embryopathy may develop when the virus is transmitted.

Results in growth retardation, microcephaly, flat nose, widespread, upward-slanted eyes.

Associated with higher rates of preterm disease, low birth weight, and miscarriage.

AIDS has slower incubation period in fetuses than adults. Symptoms often appear as early as 6 months (weight loss, diarrhea, fever, chronic infections).

Babies rarely survive more than 5-8 months once symptoms appear.

AIDS embryopathy

The Rh problem

If a woman has Rh - blood and the father has Rh +, the fetus may be born with Rh + blood.

Antibodies in the mother may attack the fetus as being “foreign.”

Can result in miscarriage, stillbirth, anemia, jaundice, heart defects, brain damage, or death soon after birth.

First Rh-positive baby is usually not affected; subsequent babies are.

Moms are given a RhoGam vaccine within 3 days of delivery to prevent antibodies from being produced.

Prematurity

Babies born 3 weeks or more before the end of pregnancy OR who weigh less than 5.5 pounds

Birth weight is best predictor of infant survival and healthy development

Best scenario is to be at least 2 pounds at birth and 32 weeks’ gestation

Preterm babies are more difficult infants than other babies are and have a greater risk for abuse.

Causes of Prematurity

Low socioeconomic status: 1 in 4 babies are born in underdeveloped countries

Infections Smoking and drinking Mom’s age (under 17 or over 35)—high

correlation Cervical problems, high blood pressure,

unusual stress, diabetes, heart diseases Often impossible to determine

Prematurity Stereotyping

The tendency for people to view premature babies as weaker, more vulnerable, and less competent than full-term babies, even after the premature babies have caught up developmentally with full-term peers

Developmental milestones may, in fact, be reached a little more slowly in preterm babies.

Experiment showed that people judged a 9-month-old healthy looking baby as “weaker, less sociable, and less cognitively competent” if told the baby had been premature.

Micro-preemie (at the very edge of viability)

This infant was born at 23 weeks and weighed 1 lb. 2.6 oz.

The same preemie at 4 years Although asthmatic and slightly

developmentally delayed, she’s doing great!

How much weight should mother gain during pregnancy? Normal weight woman: 25-35 pounds Overweight woman: 15-25 pounds Underweight woman: needs to gain to

ideal weight PLUS 28-40 pounds Exercise is okay, as long as it’s not too

strenuous. (Mild to moderate only) No exercises lying on the back after the

first trimester. Avoid exercise that affects balance.

Common Prenatal Tests

Amniocentesis: can be done from 15th week of pregnancy on. Involves taking a fluid sample of the amniotic fluid.

Alpha-feta Protein Test: (AFP)—this is a protein produced by baby’s liver; can detect spina bifida and possibly Downs Syndrome, although there are many false positives.

Chorionic villi sampling (CVS)—can test genetic structure as early as 9-10 weeks.

Three stages of birth

Stage 1: cervix dilates and effaces (thins out)…goes from totally closed to 10 cm (completely open). Lasts 12-14 hours on avg. in a first birth, 4-6 hours in subsequent births

Stage 2: the stage where the baby is pushed out. Lasts around an hour in a 1st birth, 15-20 minutes in later births.

Stage 3: placenta (“afterbirth”) is delivered. Usually occurs 5-10 minutes after baby is born; this is usually not felt by the mother.

C-sections

C-section rates are currently 20-25% in US; varies by hospital

Main reason for C-section: having had a prior C-section.

Fetal distress, prematurity, certain maternal illnesses (such as HIV), birth canal being too narrow, and labor that doesn’t progress are reasons for C-sections.

Push by some OB/GYNs to give women the right to elective C-sections.