A normal pregnancy lasts 40 weeks and is divided into 3 trimesters. The first trimester runs from conception to the end of the 13th week. This is when there is the greatest risk of miscarriage and all of the baby's organs must form. In the second trimester, from weeks 14-27, your pregnancy shows and the baby begins to move. In the third trimester, from the 28th week until birth, the baby plumps up and prepares for life outside the uterus.
First Trimester
You: The first signs of pregnancy are tender breasts, fatigue and a frequent need to urinate. At eight weeks, you might be experiencing morning sickness and food aversions, and you will probably feel deeply tired. By week 10, your uterus is about the size of a grapefruit and your clothes might feel tight. By the end of the first trimester, the chances of having a miscarriage have dramatically decreased.
The Baby: Four days after fertilization, the embryo, called a blastocyst at this point, implants in the uterus. The outer layer of cells, called the trophoblast, will become the fetal part of the placenta, while the inner mass of cells will form all the parts of the baby's body. Between weeks four to 10, all the baby's organs will form and by week 10, your doctor will be able to hear the baby's heartbeat. By the end of the first trimester, the baby is about 3 inches long and weighs about an ounce.
Second Trimester
You: In the second trimester, morning sickness usually disappears and your pregnancy starts to show. You might develop new symptoms like heartburn or back pain. You will gain weight quickly, about a pound a week. Your doctor might recommend the "triple test" and/or amniocentesis (testing of the fluid that surrounds your baby) to assess the risk of genetic defects between weeks 15-18. Most exciting, between weeks 18 to 20, you can feel your baby move for the first time.
The baby: In the second trimester, the baby grows up to about 14 inches long and by the end will weigh about 2 pounds. Bones replace her cartilage. She can suck her thumb, move her arms and legs and hear your voice. By week 18, the baby's sex is evident by ultrasound. The baby's kidneys and bowels begin to function in the last part of the second trimester. By the 27th week, the baby's lungs have started to function and with intensive support, the baby could survive outside the womb.
Third Trimester
You: In the third trimester, you will see your doctor every two weeks until week 36, when you will go weekly. With the continued growth of your uterus and the rapid growth of your baby you might feel short of breath, clumsy and fatigued again. You might begin to feel random, short and irregular contractions called Braxton-Hicks that prepare you for labor. At 37 weeks you can look for signs of impending labor, such as the baby dropping into the lower part of your uterus, or the "bloody show," vaginal discharge mixed with a small amount of blood. Your doctor will check for effacement (thinning) and dilation (opening) of your cervix to predict how close you are to labor.
The baby: In the third trimester your baby will gain about another 5 pounds and grow another 5 inches. She begins to put on some fat that will help her prepare for life outside the uterus. She might be moving enough to disturb you. At 37 weeks, the baby is considered full-term. By this time the baby is most likely in the head down position, ready for birth.
References
- "Essential Guide to Pregnancy and Birth"; Linda Murray, Leah Hennen and Jim Scott; 2005
- "Obstetrics: Normal and Problem Pregancies"; Steven Gabbe, Jennifer Niebyl and Joe Leigh Simpson; 2007
