Embryonic Period

What percent of al exposed ova to fertilization develop into recognized pregnancy?


What percent of recognized pregnancies develop and complete gestation?

< 30 %

What percent of fertilized ova fail to implant?


What percent of chromosomally abnormal embryos are naturally aborted?


When does organogenesis begin? (gestational age)

week 3

When does implantation of blastocyst occur? (LMP)

week 3

What are the three laters of the trilaminar disk?

endoderm, mesoderm, ectoderm

Heart begins to beat, primitive mouth develops, eye and nasal pit develop, and limbs develop.... (Gestational age)

Week 4-5

Oral and nasal passages confluent, spine is c-shaped, and fingers distinct and webbed .... (Gestational age)

Week 6

Beginnings of all internal and external structures are present, palate and ear visible... (Gestational age)

Week 7

Face has human appearance, external genitalia begin to differentiate... (Gestational age)

Week 8

What should the embryo length be at the beginning of week 8?

22-24 mm long

What should the embryo length be at the end of 8th week?

40 mm long

Maxilla and mandible are noted as bright echogenic structures in region of fetal face, cardiac ventricular septum closed, aorta and pulmonary trunk are divided, collecting tubules of kidneys developed, eyelids develop, upper limbs bend at elbows... (gestational age)

week 9

When should we see the double decimal sac sign? (LMP)

4.5-6th week

When should we see the GS measuring 4mm on a transvaginal exam? (LMP)

week 5

When should we see the GS measuring 4mm on a transabdominal exam? (LMP)

6-7 weeks

Embryo lies between yolk sac and amniotic sac?

Double Bleb sign

Heartbeat begins at _____ days post conception....

21 days

Heartbeat should be visualized in all embryos with a CRL of....

> 5mm

Embryo grows _______ per day...

2-3 mm

What is the equation for CRL

CRL (mm) + 42 = GA in days

Rhombencephalon is visualized, parallel echogenic lines posterior embryo represent neurall tube forming, able to recognize cranial vault... (LMP)

week 7

Embryo begins to unfold, limb buds visualized, embryonic gut herniates into umbilical cord, cerebellum may be visualized... (LMP)

week 8

Choroid plexus is visualized, spine is visualized.... (LMP)

week 10

Umbilical cord and insertion visualized, nuchal lucency posterior neck can be visualized... (LMP)

Week 11

Begins with formation of neural plate, neural folds, and ending with closure and fusion of neural tube...


Thickening of embryonic ectoderm and adjacent mesoderm...

Neural plate

An invagination of neural plate along its central axis...

Neural groove

Thickening of neural plate lateral to neural groove...

Neural fold

Fused neural folds...

Neural tube

What does the neural plate form?

-neural crest -neural tube

What is responsible for most of peripheral nervous system

Neural crest

What forms the CNS (Central nervous system: brain and spinal cord)?

Neural tube

When does the cranial end of the neural tube close?

24 days

When does the caudal end of the neural tube close?

26 days

What does the wall of the neural tube form?

brain and spine cord

What does the lumen of the neural tube form?

ventricular system and spinal canal

What are the primary brain vesicles?


What part of the brain is the prosencephalpn?


What part of the brain is the mesencephalon?


What part of the brain is the rhombencephalon?


When do the primary brain vesicles form? (gestational age)

end of 4th week

What are the 5 secondary vesicles?


What does the diencephalon consist of?

-epithalamus - hypothalamus -thalamus

When is brain development complete? (LMP)

8 weeks

When does the fetal head appear separate from the body? (LMP)

9.5-10 weeks

When is the anterior abdominal wall developed? (gestational age)

week 6

What forms majority of small bowel, cecum, ascending colon and proximal transverse colon?


When should we no longer see echogenic structures within the umbilical cord?

12 weeks

What is the most accurate measurement throughout pregnancy?

Crown rump length

What should the CRL be at 5 weeks?

2 mm

How do we determine GA in weeks (when CRL < 1)

CRL < 1.0 cm = CRL (cm) + 6

How do we determine GA in weeks (when CRL > 1)

CRL > 1.0 cm = CRL (cm) + 6.5