Week 1 HG&D

Typical human gestation is approximately __ weeks from the first day of menstruation, or __ weeks from fertilization

40; 38

When does fertilization happen?

Week 2 of gestation

When does implantation occur?

Week 3 of gestation

Gestational Age definition

Time between first day of the last normal menstrual period and delivery

(weeks are always rounded down)

Chronological Age definition

Time elapsed after birth

Postmenstrual Age definition

Time elapsed from the first day of the last normal menstrual period to birth (gestational), plus the time elapsed after birth (chronological)

Corrected Age definition

Age of infant from the expected fur date of delivery at 40 weeks

(10 weeks old but born 33 weeks of gestation = 3 weeks old)

When is the 1st trimester?

First day of last menstrual period - 12 weeks

When is the 2nd trimester?

13-28 weeks

When is the 3rd trimester?

28-40 weeks

When is the 4th trimester?

40-52 weeks post-menstrual age, or 0-12 weeks chronological age

(allows for greater environmental input during a time of incredible neuroplasticity)

Average length of gestation is __ weeks, average and healthy range is __ weeks

40; 37-42

What is considered a term pregnancy?

After 37 weeks, 0 days

What is considered a preterm delivery?

On or prior to 36 weeks, 6 days

What is considered a post-term delivery?

After 42 weeks, 0 days

What would be considered very preterm?

>32 weeks

What would be considered extremely preterm?

>28 weeks

What is the age of viability?

22-24 weeks

(World record: Iowa (21 wks), MN (21 wks, 2 days))

When is the germinal stage?

starts at conception ~ 0-2 weeks (2-4 weeks GA)

When is the embryotic stage?

3-8 weeks (5-10 weeks GA)

When is the fetal stage?

9-38 weeks (11-40 weeks GA)

What does mitosis mean?

Cell division

Normal chromosome #

46 (22 autosome pairs and 1 sex pair)

What does meiosis mean?

Reduction division

What is nondisjunction?

The chromosomes don’t separate, leading to on having an extra chromosome (47 - trisomy) and the other having none (45 - monosomy)

Karyotype vs Phenotype

Karyotype is the genetic sequence that leads to the phenotype which is the physical outcome

1st half of germinal period

Fertilization → Zygote → Cleavage → Morula → Blastocyst → Implantation

2nd half of germinal period

Implantation Completes → Embryonic Disc Formation

What are the two layers of the bilaminar embryonic disc?

Epiblast (amnion cavity on top) and Hypoblast (yolk sac cavity on bottom)

What is the most critical period of development for viable pregnancies?

Embryonic Period (3-8; 5-10 GA)

Exposure to teratogens, infection, or genetic anomalies during the germinal period leads to chromosomal changes that result in _____________

termination of pregnancy

What happens during Gastrulation?

Bilaminar to Trilaminar embryonic disc

What are the three primary germ layers and what do they turn into?

(1) Ectoderm ~ epidermis (skin) and nervous system

(2) Mesoderm ~ dermis (skin), muscles, bones, and circulatory system

(3) Endoderm ~ digestive system and lungs

What do Noggin Morphogenic proteins do?

Prevent neural stem cells from becoming epidermal stem cells by blocking BMPs in the ectoderm

What happens during Neurulation (6 GA)?

Neural tube from the neural plate ~ CNS (brain and spinal cord)

Neural crest forms the PNS

Somite formation

• Form from head to tail

• Turn into skeleton, muscle, and dermis of skin

• Consists of the blocks of mesoderm on the sides of the neural tube

Coelum (cavity) formation

• Pericardial

• Pleural

• Peritoneal (upper and lower)

What do Hox Morphogenic Proteins do?

Signal changes in segments; Top Down/Bottom Up

What do sonic Hedgehog genes do?

Block BMPs ventrally allowing ventral/dorsal development

When does the first heartbeat begin?

21 days after fertilization (5 weeks GA)

How large is the embryo at the 6th week?

Poppy seed (2-3 mm)

What happens at week 7?

Sideways movement

How large is the embryo at 8 weeks?

Skittle or baked bean

What happens in the 9th and 10th week of gestational age?

Tail disappears & human characteristics are visible

• Eyes, ears, lips, nose, neck, and external genitalia (gender indistinguishable)

11-14 Weeks (gestational age)

Intestines move internally in the abdomen

14th Week - about the same size as a _______

Fun sized candy bar

15 - 18 Weeks (gestational age)

• Recognizable genitalia (wk 16)

• M health will perform fetal surgery to repair spinal lesions in utero (wk 18)

19 - 22 Weeks (gestational age)

• Lanugo and vernix caseosa cover; form barrier protecting skin from amniotic fluid

• Begin hearing noises

20 Weeks (gestational age) - revise and adjust

• End of spinal cord is at S1; marked by the filum terminalae

  • At Birth: At level L3

  • Adulthood: Will migrate to L1-L2

23-27 Weeks

• Lungs produce surfactant by 26 weeks

• Viability edge is 22 weeks

  • 500g is around 1 lb

• 1000g is extremely low birth weight (ELBW)

• 2400g is considered normal

Born under 1500 grams experience

• Intrauterine growth restriction

• highest risk of pulmonary, neurological, and gastrointestinal pathology

• Most significant development delays

• Highest risk of vision and hearing loss

DPT connection to <1500g births

• 47% chance of a multiple domain developmental delay

• Increased risk of mild motor delays not associated with CP

• Significantly increased incidence of autism, cerebral palsy, developmental coordination disorder, cognitive delays, and ADHD

28-31 Weeks

Pre-term infants can move their legs against gravity at 30 weeks

32-36 Weeks

• Preterm infants can move their trunk against gravity at 32-34 weeks

• Upper extremity movement against gravity at 35 weeks

• Infants born at 32 weeks gestation will begin “back to sleep” in NICU

What is the “back to sleep” in NICU

Sleeping on back to prevent sudden infant death syndrome

36-38 Weeks (revise)

• Normal full-term weight 3400g

• Normal height 18-22 inches

• Infant is able to regulate their:

  • Temperature, muscle tone, arousal states

    • necessary to interact with and learn from their primary caregivers

Physiological flexion

Midline stability: feeding, self-regulation, and parent-infant interactions

• Preterm infants never experienced the assisted recoil of the womb; extend their extremities and the womb assists with returning to a flexed position