PregnancyPregnancy is divided into three trimesters that coincide with fetal development stages and certain fetal/maternal tests.

First Trimester of Pregnancy

Weeks one through 13 make up the first trimester. During this time, the fetus follows a predictable course of development:

Fetal Development During the First Trimester

Weeks one and two technically are counted prior to conception, so fertilization and implantation typically occur around weeks three and four. Throughout the rest of the pregnancy’s first trimester, the embryo’s anatomy forms including the face, brain, eyes, ears, toes and fingernails will begin developing.

Testing During the First Trimester

The start of the first trimester often begins with a pregnancy test.  During the first visit, blood tests, a family history, pelvic exam and breast exam are common. Other first trimester visits often include weight and blood pressure measurements, as well as urine tests.

Second Trimester of Pregnancy

The second trimester consists of weeks 14 through 27:

Fetal Development During the Second Trimester

As the pregnancy progresses into the second trimester, the fetus’s skeleton develops bones; sex becomes visible; fat stores, skin and the swallowing reflex develop; and the fetus is able to hear. At week 26, approximately 77% of babies born are able to survive with medical support.

Testing During the Second Trimester

Regular measurements are taken to monitor the fetus’s size, heartbeat, and movement. Various prenatal tests may be recommended, to include ultrasound, fetal genetic testing/screening, and a glucose tolerance test (for gestational diabetes).

Third Trimester of Pregnancy

The third, and final, trimester of pregnancy consists of weeks 28 through 40:

Fetal Development During the Third Trimester

During the last trimester, the fetus will continue putting on weight; open his eyes and practice breathing as the lungs continue to mature.  The placenta supplies the fetus with antibodies. The due date is calculated as 40 weeks from the last menstrual period.

Testing During the Third Trimester

Weight and blood pressure screening will continue throughout the pregnancy. In addition, it is common to monitor fetal heartbeat and movement. Group B streptococcus (GBS) tests are common in the last trimester because the infection can be serious for babies after birth. Also, pelvic exams will be reinstated to monitor the changes in the cervix and the fetus’s position.