FETAL DEVELOPMENT

EMBRYONIC PERIOD

starts at the beginning of the second week after ovulation and ends at approximately 10 gestational weeks

PREVIABLE FETAL PERIOD

last from 11 to 19 gestational weeks

VIABLE FETAL PERIOD

lasts from 20 to 40 gestational weeks

GESTATIONAL AGE

also known as menstrual age and age of gestation

GESTATIONAL AGE

is calculated from the first day of the last menstrual period (LMP)

GESTATIONAL AGE

is generally used in clinical practice

280, 40, 9 1/2, 10

Pregnancy lasts for about __ days, or weeks, calendar months, or _ lunar months, when calculation is made from the LMP.

GESTATION

comes 2 weeks after the LMP

GESTATION

It is 2 weeks less than the gestational age

0-2 DAYS AFTER OVULATION

fertilization of the ovum takes place

ampulla

fertilization takes takes place usually in the ___ of the fallopian tube

ZYGOTE (STAGE 1)

This is what fertilized egg become

ZYGOTE (STAGE 1)

It then undergoes a series of mitotic cell divisions as it travels toward the uterine cavity

BLASTOMERES

a cell formed by cleavage of a fertilized ovum.

2-4 DAYS AFTER OVULATION & FERTILIZATION

 the zygote enters the uterine cavity

MORULA (STAGE 2)

a solid ball of 12-16 cells 

MORULA (STAGE 2)

solid mass of blastomeres resulting from a number of cleavages of a zygote, or fertilized egg.

4-6 DAYS AFTER OVULATION & FERTILIZATION (STAGE 3 & 4)

morula acquires 0 fluid-filled cavity, called the blastocyst 

TROPHOBLAST

distinct outer cell layer 

END OF 1 WK/7 DAYS AFTER OVULATION & FERTILIZATION

 the blastocyst implants, usually in the midportion of the uterus.

6-12 DAYS (STAGE 5)

2nd week after ovulation, the embryo continues developing.

NEURULATION BEGINS

The early stage of forming the brain and spinal cord.

SOMITES FORM

These are blocks of cells that will develop into the spine, muscles, and skin.

END OF 4TH WEEK AFTER OVULATION (6TH WEEK OF GESTATION)

The embryo has a C-shaped curvature.

END OF 4TH WEEK AFTER OVULATION (6TH WEEK OF GESTATION)

Arm and leg buds are visible.

END OF 4TH WEEK AFTER OVULATION (6TH WEEK OF GESTATION)

The body stalk has 1 umbilical vein (carries oxygenated blood) and 2 umbilical arteries (carry deoxygenated blood), which will become the umbilical cord.

AMNION

unsheathes the body stalk, forming the umbilical cord.

END OF 8TH WEEK GESTATIONAL AGE (AOG)

Embryo is 22–24 mm long.

END OF 8TH WEEK GESTATIONAL AGE (AOG)

Head is large compared to the trunk.

END OF 8TH WEEK GESTATIONAL AGE (AOG)

Fingers and toes are visible.

END OF 8TH WEEK GESTATIONAL AGE (AOG)

External ears appear as elevations on both sides of the head

END OF 10 WEEKS AOG

Organogenesis is complete

END OF 10 WEEKS AOG

Crown-rump length (CRL): 30 mm.

END OF 10 WEEKS AOG

Head is rounded, eyelids fused, ears fully developed.

END OF 10 WEEKS AOG

Fingers and toes well formed.

FIRST 8 WEEKS OVULATION AGE / 10 WEEKS AOG

Period of differentiation: all birth structures are formed.

FIRST 8 WEEKS OVULATION AGE / 10 WEEKS AOG

Teratogens (e.g., infections) only affect development if the structure is still forming.

11 WEEKS AOG

Head = ½ of CRL, eyes closed.

11 WEEKS AOG

External genitalia not yet distinguishable.

12  WEEKS AOG

Ossification centers in most bones.

12  WEEKS AOG

Fingers and toes differentiated.

12  WEEKS AOG

Sex organs distinguishable, gross movements, sucking respons

16  WEEKS AOG

Sex can be seen externally.

16  WEEKS AOG

Fingers flexed, limbs crossed.

16  WEEKS AOG

Skeleton visible by x-ray.

Lanugo

covers body, scalp hair present.

20 WEEKS AOG (MIDPOINT OF PREGNANCY)

Regular fetal breathing movements begin.

24 WEEKS AOG

Wrinkled skin, eyebrows/eyelashes visible.

24 WEEKS AOG

Surfactant production begins.

24 WEEKS AOG

Survival possible with intensive neonatal care.

28 WEEKS AOG

Thin red skin, covered with vernix caseosa.

28 WEEKS AOG

Eyes partially open, eyelashes present.

32 WEEKS AOG

Skin red and wrinkled, toenails present.

32 WEEKS AOG

Testes begin to descend.

36 WEEKS AOG

CRL: 32 cm, weight: ~2500 gm.

36 WEEKS AOG

Fat deposited, skin no longer wrinkled.

36 WEEKS AOG

Fingernails reach fingertips

40 WEEKS AOG (FULL TERM)

CRL: 36 cm, weight: ~3400 gm.

40 WEEKS AOG (FULL TERM)

Testes in scrotum, breasts protrude, pinnae with cartilage

40 WEEKS AOG (FULL TERM)

Fingernails extend beyond fingertips.

40 WEEKS AOG (FULL TERM)

Fetus is fully developed.

FETAL HEAD

Most important part during labor for passage through the birth canal.

FETAL HEAD

Made of 2 frontal, 2 parietal, 2 temporal bones, part of occipital, and sphenoid.

• Frontal suture

• Coronal sutures

• Lambdoid sutures

Sutures are membranous gaps between bones

FONTANELS

Soft spots where multiple sutures meet

Anterior (bregma)

diamond-shaped

Posterior

triangle-shaped

Temporal (casserian)

at lambdoid and temporal junction

Occipitofrontal diameter (OFD)

11.5 cm

• Biparietal diameter (BPD)

• Suboccipitobregmatic diameter (SOB)

• Trachelo-bregmatic diameter (TBD)

9.5 cm

Bitemporal diameter (BTD)

 8.0 cm

Occipitomental diameter (OMD)

12.5 cm

Greatest head circumference (OFD plane)

~34.5 cm

Smallest circumference (SOB plane

~32 cm