Fertilization occurs when a women’s egg (ovum) and man’s sperm (spermatozoon) join. This results in what is called a zygote that travels down through the fallopian tubes to the uterus and implants itself to the wall of the uterus. The zygote releases hormones, which stops the woman from having her period. This is the point the women is considered pregnant
(Pillitteri, 2007).

First Trimester (Week 1-12)

• Week 4 the zygote is growing and is only 1 cm long
• It has yet to take human form
• Week 8 the heart is beating in rhythm
• Able to make out facial features
• Weighs 20 grams, about the same as 3 cubes of sugar
• Week 12 is the end of this trimester
• Heartbeat can be heard with a doppler
• Eyelids are closed
• The buds of teeth have come through
• Movement of the fetus possible, but will probably not be felt
• Fetus is about 7-8 cm long
• Weighs 45 g, about 6 cubes of sugar
  
  
  

  Second Trimester (Week 13-24)

• Week 16 the sex of the fetus can be determined
• Heartbeat can now be heard with a stethoscope
• Lanugo is established at this time
• Week 20 the hair is forming (including eyebrows!)
• Vernix begins to form
• Meconium is present in the intestine
• Brown fat begins to deposit in target areas
• Weighs 223 g about the same as a cup of rice
• Week 24 the fetus is 28-36 cm long
• Eyelids are now open
• Can begin to hear noises by this week
• Meconium is now present in the rectum
  
  
  

  Third Trimester (Week 25-40)

• Week 28 the fetus is 35-38 cm long
• Weighs 1,200 g, the same as about 8 cups of raisons
• Lungs are beginning to mature and surfactant is present in amniotic fluid
• Retinal blood vessels are very immature
• Week 32 fetus is 38-43 cm long
• Weighs 1,600 g
• Can respond to “outside” noises
• Has formed fingernails
• Week 36 fetus is about 5-6 lbs
• Fetus is 42-48 cm long
• Usually moved into the birthing position with its head down (but may be breech)
• Continues to grow
• Week 40 the fetus is 48-52 cm long
• There is lots of movement and kicking
• Vernix is fully present
• Lanugo is almost all gone
  
  
  (American Pregnancy Association, 2005, 2007a, 2007b; Pillitteri, 2007)