First Trimester:

Mother:

• The breasts will start to change, becoming larger, and tender as hormone changes cause changes in breast tissue. This is to prepare them for breastfeeding. The pigment of the areola may also get darker, and small lumps may appear called Montgomery's tubercles.
  
  
• Nausea and vomiting may occur at any time of the day usually lasting 8-12 weeks. 
  
  
• Mother may feel very tired as her energy demands increase. 
  
  
• Some women experience headaches as a result of the physical and emotional changes.
  
  
• A dark line may appear from your navel downward (linea nigra)
  
  
• Increased frequency of urination due to pressure on the bladder

Baby:

• By eight weeks the fetus has all the organs including the heart that is already pumping. Bone formation has begun.
  
  
• By twelve weeks, the baby's sex can be determined. The baby teeth are present in the gums. Fingernails and toenails are forming. The baby can move in the amniotic fluid, but the movements are small and cannot be felt by the mother.
  
  
• The baby is 9cm or 3.5 inches, and weighs 15 grams or 0.5 oz

Second Trimester:

Mother:

• The uterus has risen in the abdomen decreasing pressure on the bladder
  
  
• The breasts may begin to secrete colostrum
  
  
• The mother may feel the baby's movements now.
  
  
• The mother may experience back and leg pain, constipation, varicose veins, or mild swelling of the ankles, feet, hands, and face.

Baby:

• The head has hair, as do the eyebrows and eyelashes.
  
  
• The baby's heartbeat can be heard with a stethoscope.
  
  
• The baby's movements can be felt by the mother.
  
  
• The baby is 30cm or 12 inches, and weighs 600 grams or 1 1/4 lb by 24 weeks.
  
  
• By 26 weeks, the baby's outline may be felt through the abdomen.

Third Trimester:

Mother:

• Irregular, painless contractions of the uterus may be experienced. (Braxton Hicks contractions)
  
  
• Heartburn, haemorrhoids, shortness of breath, and difficulty sleeping may be experienced in the early part of the third trimester.
  
  
• Toward the end of the third trimester, breathing may improve due to the uterus settling down into the pelvis, this may also cause an increase in frequency of urination.

Baby:

• The baby becomes aware of sounds outside the body, the pupils can react to light
  
  
• The baby stores fat under the skin
  
  
• The baby increases the store of maternal antibodies and thus resists some diseases.
  
  
• By 40 weeks, the baby is 45-55cm long (18-22in.) and usually weighs at least 3200g or 7lbs.

For More Information:

Go to Baby's Best Chance pages 21-33

or Week by Week Guide for each of the forty weeks of pregnancy, you'll find information about baby's development.