There are about 40 weeks between the first day of the last menstrual period and the birth of the baby. The mother's and baby's bodies undergo a vast array of changes during this time. The stages of pregnancy are often divided into three stages, and each stage is often referred to as a trimester; each trimester is about three months long.
First Trimester
The first trimester encompasses the first three months of pregnancy. According to information provided by the Nemours Foundation, there are many changes that occur during this period. The egg is fertilized by the sperm, and then goes through extensive cell division and implants in the uterus during the first month. The new mother may begin to feel fatigue, sensitive breasts and nausea. In the second month, the Nemours Foundation reports that the embryo's distinctive baby shape begins to form, along with the brain, spinal cord, digestive tract and lungs. In the third month, vital organs, a beginning of teeth and tiny finger and toe nails form.
For the mother, fatigue, sensitive or aching breasts and/or nausea commonly make up so-called morning sickness during these three months. The National Women's Health Information Center also reports that headache, heartburn, weight gain or loss, and the frequent need to urinate is common during this period.
Second Trimester
The fourth through sixth months of pregnancy comprise the second trimester. The Nemours Foundation reports that the baby's genitals fully develop during this time, and fine colorless hairs begin to develop in the fourth month. According to a guide provided by Sutter Health, the mother may feel the fatigue and nausea of the earlier months begin to dissipate. Also, the growing baby begins to make the mother's body larger. The Sutter Health guide also reports that, during the fifth month, the breasts may start to leak a fluid called colostrum. According to the NWHIC, the hands may begin to feel numb or tingling around this time, and body aches and stretch marks may begin. Swelling of the ankles, fingers and face may also occur. In the sixth month, the baby's senses begin developing, he will soon start to hear and feel, and he begins to move his muscles.
Third Trimester
According to the Nemours Foundation, the baby's eyes will may start to open and blink in the seventh month, and she may now start to recognize her mother's voice. Also during the seventh month, layers of fat are added to the baby's body, and the brain further develops. The baby's movement often becomes more vigorous and forceful. In the eighth month, the baby begins to urinate into the amniotic sac, and eyelashes and hair are recognizable. The baby's eyes can sense light, and even his pupil's can dilate. The baby's lungs continue the last stages of maturation. In the last month or so, the baby usually repositions herself head-down and gains a large amount of weight.
