First Trimester• 5 week embryo• ~ 1 month = 7 mm• Brain and spinal cord• 4 limb buds, short tail and

gill pouches

•9 week Fetus ~5.5 cm

•Placenta, umbilical cord, amnion

•All organs and body parts

•Can move

Second Trimesterincrease in size and refinement

• Ultrasound – 18 week fetus, can show sex or abnormalities

•14 week fetus ~ 6 cm

•20 week fetus ~ 19 cm

•~ ½ kg (1 lb)

•Nails, eyelashes, covered with hair

Third Trimester rapid growth

• Premature babies

• 24 weeks may survive with medical care

• Circulatory and respiratory systems prepare for breathing air

• Rotates head toward cervix

• At birth ave =

– 50 cm (20 in)

– 2.7-4.5 kg (6-10 lb)

Childbirth• Labor – strong

rhythmic contractions of the uterus controlled by hormones

1. Estrogen - Induce oxytocin receptors

2. Oxytocin – causes uterus to contract, placenta to make prostaglandins (more contractions)

Childbirth…1. Cervix dilates (0 to ~10 cm),

ave. 6-12 hours

2. Full dilation of cervix to birth, strong contractions, ave. 20 – 60 minutes, clamp umbilical cord

3. Delivery of the placenta (afterbirth), ~ 15 minutes after birth

Hormones after birth…

• Estrogen and progesterone allow uterus to return to pre-pregnancy state

• Prolactin – promotes milk production in mammary glands – colostrum (protein and antibodies) before milk– Milk comes in ~2-3 days after birth