When does the second and third trimesters in pregnancy start?

A pregnancy is divided into trimesters. Three trimesters make up the entire duration of the pregnancy. The first trimester begins from the first week and lasts until the twelfth week. The second trimester begins from the thirteenth week and continues till week 26, and the third trimester begins from week 27 and lasts until the delivery.

In the first trimester the fertilized egg attaches itself to the wall of the uterus. As this happens, the amniotic sac encompasses the egg and the placenta begins to grow in order to provide nourishment and remove waste. The umbilical cord supplies oxygen and other nutrients to the embryo which will soon start developing into a baby. The second trimester starts in the fourth month of pregnancy. The baby at this time weighs around six ounces. Growth starts taking placing rapidly and the umbilical cord also grows to meet the developing baby’s nutrient requirements. This is also the time when the symptoms of pregnancy experienced in the first three months begin to subside. Morning sickness and tiredness no longer occur as the body becomes accustomed to the changes. The mother will also gain weight and it is common to start experiencing the movements of the body.

During the fifth and sixth month, further development occurs and the baby’s features become developed. The baby is mostly fully formed by now and the brain tissue starts to increase.

The third trimester begins in the seventh month of pregnancy. The baby begins to stretch and kick and will also start changing positions. The mother’s weight will continue to increase. In the eight month, the baby will grow 16 inches in length and will weigh about 4 pounds. The breasts of the mother will begin to prepare for milk production. The baby starts to develop fat and begins to resemble a newborn now. In the ninth month, the baby moves down into the mother’s pelvis to prepare for delivery. The mother needs to visit the doctor every week until the birth. The baby continues to grow during this time, but as there is less space, the movements may not be felt. Towards the end of the third trimester, the head of the baby will be lodged into the pelvis. Immunity is not fully developed and the placenta continues to supply the baby with antibodies. In this final stage of pregnancy, the mother gains 25-30 pounds, of which 7 ½ pounds will be the baby’s weight. False labor contractions commonly occur during this time. Once the contractions begin to occur in a consistent pattern, delivery is likely to occur soon.

Submitted by P T on January 13, 2010 at 10:57

Read more questions in Pregnancy Trimester