Trimesters and Due Date

Written by Tracy Stickler | Published on March 15, 2012
Medically Reviewed by Jennifer Gunter, MD, OB/GYN

Trimesters

A normal, full-term pregnancy is anywhere from 37-42 weeks, and is divided into three trimesters. Each trimester lasts between 12 and 14 weeks.

First Trimester

The first trimester lasts from the first through the 13th week of pregnancy. Although you may not look pregnant during the first trimester, your body is going through enormous changes as it accommodates a growing fetus. In the first few weeks following conception, your hormone levels change significantly, your uterus begins to support the growth of the placenta and the fetus, your body begins to make more blood in order to carry oxygen and nutrients to the developing baby, and your heart rate increases. These changes can cause the onslaught of pregnancy symptoms, such as fatigue, morning sickness, headaches, and constipation.

Read about the first signs of pregnancy, and what you can do to help ensure a healthy pregnancy »

The first trimester is vital for the development of your baby. The fetus will develop all of its organs by the end of the third month, so it's particularly vulnerable at this time. It's important to maintain a healthy diet, including adding an adequate amount of folic acid in order to help prevent neural tube defects. Cut out any bad habits, such as smoking and alcohol use which have been related to serious complications in pregnancy and birth defects.

Read how your baby is developing each week in our pregnancy calendar »

Second Trimester

Often called the "golden era," the second trimester (weeks 13–27) is the most comfortable period of time for the majority of pregnant women. Most of the early pregnancy symptoms will gradually disappear, and you should enjoy a more restful night's sleep and a surge in energy levels during the daytime.

Your abdomen will start to look pregnant, as the uterus will rapidly grow in size. At the end of the second trimester, your baby will be almost four times as big as it was at the end of the first trimester. It's a good time to invest in maternity wear, and spread the good news of your pregnancy with your friends and family.

While the discomforts of early pregnancy should ease off, there are a few new symptoms to get used to. Common complaints include leg cramps and heartburn.

Screening tests are also performed in the second trimester, and this is when a diagnostic test would be performed. Be sure to talk to your doctor about your medical history and any issues that could put you or your baby at risk.

Third Trimester

The third trimester lasts from the 28th week through the birth of your baby. During the third trimester you will start seeing your health care provider more frequently. Your doctor will regularly test your urine for protein, check your blood pressure, listen to the fetal heart rate, measure your fundal height (the approximate length of your uterus), and check your hands and legs for any swelling.

Your doctor will also determine the baby's position and check your cervix in order to monitor how your body is preparing for childbirth.

The third trimester is a good time to educate yourself about labor and delivery. Take time out to enroll in a childbirth class. Childbirth classes are designed to prepare you and your partner for labor and delivery. It's a great way to learn about the different stages of labor and delivery options, and gives you the opportunity to ask any questions or voice any concerns to a trained childbirth instructor.

Due Date

A normal, full-term pregnancy can last anywhere from 37 to 42 weeks. Your due date is really an estimated date of delivery (EDD) and is dated from the first day of your last period, even though you actually conceive two weeks or so after this date (depending on the length of your cycle). The dating system works well for women who have fairly regular menstrual cycles. However, for women who have irregular periods, the dating system may not work and other methods may be needed to determine the EDD. The most accurate method of determining the due date is an ultrasound in the first trimester, because early fetal development is fairly regular across all pregnancies.

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