Chapter 7 - Ninth week to Birth

Premature birth

Before 37 weeks

Nonviable birth

Before 24 weeks

In the fetal period, the focus shifts from organogenesis to what?

growth and tissue maturation

What rapidly increases during the fetal period?

Body size

Weight

-especially during final weeks

How much weight is gained per week from weeks 30-38?

½ lb

Fertilization age

38 weeks

Gestational age (LNMP)

40 weeks

Trimesters

Three 3-month intervals

Embryonic to Fetal Development

How large is the head at 9 weeks?

½ CRL

Body length nearly doubles by what week?

12 weeks

When do cranial bones begin ossifying?

During weeks 9-11

When is the brain fully grown?

6 years old

Allometry

How much one thing grows relative to another

Fetal facial development during weeks 9-12

• Eyes are widely spaced

• Ears lowset

• Eyelids are fused

Fetal Limb development during weeks 9-12

• Upper limbs near final relative length; 70% of lower limb length

• Lower limbs shorter

When is external genitalia distinguishable?

End of week 12

Intestine development during weeks 9-12

• Temporary herniation into umbilical cord

• Return to abdomen by week 11

• Stomach starts as one tube and rotates during development

Urine development during weeks 9-12

• Swallowed amniotic fluid recycled by the placenta

• Fetus with kidney problems usually result from less surrounding amniotic fluid and swallowing urine

Oligohydranamus

Low amniotic fluid

Internal fetal development occurs in weeks

9-12

When does rapid growth and earl movement occur?

Weeks 13-16

Coordinated limb movements occur by which week?

Week 14

• Visible on ultrasound

• not yet felt by mother

When are bones visible on ultrasound?

16 weeks

When does quickening occur?

Weeks 17-20

When are the first fetal movements felt by the mother?

Weeks 17-20

What is quickening?

Baby can be felt by the mother

Quick

Living

When do skin adaptations occur?

Weeks 17-20

Vernix Caseosa

• Water

• Lipids

• Dead skin cells

Covers baby at birth

Vernix

Coating

Caseosa

Cheese

Lanugo

• Fine fetal hair

• Helps hold vernix against the skin

Thermoregulation

Preparing for life after birth occurs when?

Weeks 17-20

What occurs to prepare for birth in weeks 17-20

Brown fat begins to form

• Important for heat production after birth - Thermoregulation

Approaching viability occurs during which weeks?

Weeks 21-25

What growth changes occur during weeks 21-25?

Significant weight gain

What appearance changes occur during weeks 21-25

Skin:

• Think

• Wrinkled

• Reddish

Little subcutaneous fat

Underlying blood vessels remain visible

Singleton vs Dichorionic Twins vs Monochorionic Twins

Lung maturation occurs when?

Weeks 21-25

Lung maturation

• Type II pneumocytes begin secreting surfactant by ~24 weeks

-fetus not viable before this

• Surfactant reduces alveolar surface tension

• Helps prevent alveolar collapse

Alveoli

Ends of our lungs where O2 + CO2 exchange occur

Cohesion

H20 sticking to eachother

What does the surfactant do?

Breaks apart H2O

When does viability occur in infants?

Week 24

Birth at week 24

• Survival possible with intensiveneonatal care

Major risks include:

• Respiratory distress (NRDS)

• Brain hemorrhage: vessels not fully developed

• Sepsis

• Long-term neurodevelopmental

impairments

Continued Maturation occurs when?

Weeks 26-29

When do eyelids open

During weeks 26-29

When are lungs capable of gas exchange?

During weeks 26-29

When does the CNS continuously control rhytmic breathing and body temperature?

During weeks 26-29

When is there more subcutaneous fat?

During weeks 26-29

SIDS

sudden infant death syndrome

-medulla isn’t fully matured until 6 months after birth and it dictates rhythmic breathing

How can SIDS occur?

Babies that are covered in blankets can breathe in their own CO2 and this causes their blood to become acidic

-also stomach sleeping for babies is dangerous

When does Late Fetal Development occur?

Weeks 30-38

When does the pupillary light reflex present

30 weeks

By what week would most fetuses survive if born?

32 weeks

What else occurs during late fetal development?

subcutaneous fat increases and continued organ maturation

When are fetuses full term?

~38 weeks after fertilization or ~40 weeks gestational age

Average weight at birth

7.5 lbs or 3,400 grams

What is the appearance of the body at birth

Rounded

9-12 weeks snapshot

Rapid growth and changing proportions

13-20 weeks snapshot

Coordinated movement → quickening

21-25 weeks snapshot

Lung maturation and potential viability

26 weeks → birth snapshot

Functional maturation and fat accumulation

Factors influencing fetal growth

Genetic

Placental

Environmental

IUGR

Intrauterine Growth Restriction

-Fetus is too small

Macrosomia

Fetus is too large

Multiple pregnancy leads to

Lower birth weight

Maternal diabetes leads to

Larger

Ultrasonography

Used throughout the pregnancy to assess changes in the fetus

Early pregnancy ultrasonography

Around week 8 to determine:

• Viability

• Gestational age

Mid pregnancy ultrasonography

Around week 18 to determine:

• Fetal anatomy

Later pregnancy ultrasonography

Around week 30 to determine:

• Growth

• Placenta

• Presenation: direction baby is facing

What are the different fetal presenations

1.) Cephalic: Head first

2.) Breech: Feet first

3.) Transverse: Shoulder first

Chorionic Villus Sampling (CVS)

• Samples Chorionic villi

• Around 8-10 weeks

Used for:

• Chromosomal abnormalities

• Inherited genetic disorders

1% spontaneous abortion risk

Amniocentesis

• Samples amniotic fluid

• Around 13-16 weeks

• Provides fetal cells for genetic/chromosomal testing

• Amniotic fluid can be tested for AFP

0.5% spontaneous abortion risk

Percutaneous Umbilical Blood Sampling

Samples fetal blood in the umbilical vein

Around 16 weeks

Used to evaluate:

• Fetal infections

• Blood disorders

• Genetic abnormalities

1.3% risk of spontaneous abortion

Alpha-fetoprotein (AFP) assay

Optimal around weeks 16-19

• Neural tube defects

• Ventral wall defects

Cell-free DNA/Noninvasive prenatal (NIPT) Screening

>10 weeks

• Fetal DNA in maternal blood (up to 27 years later)

• screens for common trisomies (13, 18, 21)

Fetal monitoring

• Monitors fetal heart rate

• Abnormal patterns may indicate fetal distress

MRI

• Complex fetal abnormalities

• Fetal surgery planning

Neonatal Period occurs when?

Birth to 4 weeks

What occurs at birth?

• First breath

• Fetal circulatory shunt begins to close

Early neonatal period

• Cord falls off ~ 7-8 days

• 10%weight loss normal

Late neonatal (7–28 days)

Reflexes:

• Grasp

• Rooting

• Turn toward cheek stimulus