Misconceptions about

Conception

Menstrual cycle is not always 28 days.

Ovulation does not always occur on day 14.

It is true that there is a fixed amount of time between ovulation and menstruation, usually

12-16 days.

Conception can only within 24 hours after ovulation; however, women are considered

“fertile” for 2-3 days before ovulation.Maximum fertile day is day of ovulation.

Necessary ingredients to conception

An ovum, or egg that has been released

Sperm (average ejaculate contains 300-

350 million sperm)

Fertile-quality, “eggwhite” cervical fluid for the sperm to swim in

Fertile quality cervical fluid

Where conception occurs

Once the egg has been released, it is pulled from the ovary into the fallopian tube.

Most conceptions occur in the outer third of the fallopian tube.

The fertilized egg is called a zygote.

Corpus luteum

When the egg is released, a yellow spot is left behind on the ovary where the egg was. This is the corpus luteum.

Function of the corpus luteum: to secrete hormones to prepare the uterine lining to receive a fertilized egg.

If fertilization does not occur

The corpus luteum shrinks

Progesterone levels fall dramatically

Uterine lining is discarded through the menstrual cycle approximately 14 days past ovulation.

Zygote’s journey to the uterus

It takes 7-9 days for zygote to go from the fallopian tube to the uterus

Pulled along by the cilia of the fallopian tube

Then it implants in the uterine wall.

If you experience spotting (light bleeding) about 7-9 days after you ovulate, then there’s a good chance you’re pregnant. Called implantation bleeding.

hCG

After the zygote has burrowed into the uterus, it starts releasing human chorionic gonadotropin hormone (hCG)…the pregnancy hormone.

It is the presence of this hormone that pregnancy tests detect.

Function of hCG is to send a message back to the corpus luteum to stay alive and start producing progesterone.

Role of Progesterone

Progesterone keeps the uterine lining from shedding.

Many very early miscarriages result from lack of progesterone.

Taking progesterone supplements in early pregnancy can prevent a miscarriage.

Placenta eventually takes over progesterone production from the corpus luteum.

Fertility rates by age

Age

15

Rate per cycle

40-50%

25 30-35%

35 15-20%

45 3-5%

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

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.

The embryo at 6 weeks

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.

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 (5

th

-6

th

month)

12-15 inches long, 12-32 ounces

Grasping reflex

Lung breathing is possible

Sleep/wake cycles similar to newborn’s

Eyes and ears are sensitive to light and sound

Grasping reflux; baby sucks thumb

All neurons present by 24 weeks’ gestation

Vernix and lanugo

Appear in 5 th -6 th 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 24 th week, the fetus has a 50% chance of survival.

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

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.

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

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.

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.

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 1 st 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.