Embryonic & Fetal dev. Wks 4-8

Question 1

What is another name for gestational age?

What is this?

Answer 1

Gestational age=Menstrual age:

The age calculated since the first day of Last Normal Menstrual Period (LNMP).

Question 2

How long is the length of pregnancy according to the gestational age?

How long is the length of pregnancy according to the embryonic/fetal/conceptual age?

Answer 2

The length of pregnancy is the date of LNMP to birth (280 days or 40 wks);

The length of pregnancy is from date of fert. + 266 days, or + 38 wks

Question 3

How would you count the embryonic age?

Answer 3

Count forward 14 +/- 2 days from the time since LNMP.

eg LNMP Feb 14 estimated, gestational age 6 wks,

estimated date of conception=Feb 28, estimated conceptual age =4 wks

Question 4

Into what wks are the trimesters divided?

Answer 4

1st trimester: LNMP to 14wks gestational age (12 wks fetal age)

2nd trimester: 14 to 26 wks gest. age (24 wks fetal age)

3rd trimester: 26 to 40 wks gest. age (38 wks fetal age)

Question 5

What is Nägele’s rule?

Answer 5

It is used to calculate the due date;

First day of LNMP - 3 mo + 1 yr + 7 days

eg: First day LNMP= Aug 20, 2011,
- 3 mo= May 20, 2011,

+ 1yr= May 20, 2012

+ 7 days= May 27, 2012

Question 6

What is quickening and when does it happen?

Answer 6

Fetal movements felt by the mother; usually felt at approx 17-20 wks

Question 7

When is the organogenetic period?

Answer 7

wks 4 thru 8 of conceptual age.

NOTE: Embryo is extremely susceptible to teratogens in this period

Question 8

When is the fetal period?

Answer 8

Wks 9 thru birth; Embryo now called fetus (after beginnig of wk 9)

NOTE: As a result of the morphogenetic processes of wks 4-8, the embryo is recognizably human by beginning of wk 9, and is now referred to as a fetus

Question 9

What is the carnegie embryonic system?

Answer 9

It is a system to determine the age of an embryo based on physical appearance

Question 10

What are the 3 different common measurements for an embryo?

Answer 10

1. Greatest length: used primarily for young embryos that haven’t yet folded
2. Crown-rump length: (most frequentlly used) sitting height
3. Crown-heel length: standing height

Question 11

What are the external characteristics and important events for wk 4?

Answer 11

Characteristics:

1. Upper limb buds flipper-like, lower limb buds appear
2. 4 pairs pharyngeal arches visible
3. otic vescicle, lens placodes present

EVENTS:

Embryonic folding

Question 12

What are the external characteristics and important events for wk 5?

Answer 12

Characteristics:

1. Head enlarges, face contacts heart prominence
2. Mesonephric ridge marks kidney developmnt

Question 13

What are the external characteristics and important events for wk 6?

Answer 13

Characteristics:

1. Digital rays present in hand
2. Elbows and hand plates appear
3. Auricular hillocks appear and eye is clearly visible

EVENTS:

Dental laminae form, reflex response to touch

Question 14

What are the external characteristics and important events for wk 7?

Answer 14

1. Epidermis has 2 layers
2. Fingers separate, digital rays on foot
3. Scalp vascular plexus

EVENTS:

Intestines herniate into umbilical cord; ossification begins in UPPER limbs

Question 15

What are the external characteristics and important events for wk 8?

Answer 15

Characteristics:

1. Digits of hands are webbed, notches appear in feet
2. Caudal eminence disappearing
3. Eyelids closing

EVENTS:

Ossification begins in LOWER limbs