The first trimester encompasses weeks zero through twelve, the second trimester will include weeks 13 through 27 and the third trimester will cover from week 28 up to the birth of your baby. This stage of pregnancy is crucial to the development of the fetus. Although you may not look pregnant, there are major changes occurring to both the mother and the fetus. For the first eight weeks, the fetus is called an embryo. This embryo rapidly develops into a fully formed fetus. The first trimester is when the fetus is most vulnerable as all of the major organs and body systems are forming. It’s important that alcohol, tobacco, drugs and radiation are avoided.
The Embryonic StageDuring the week after fertilization, the fertilized egg will implant into the uterine wall. In the first four weeks all of the major organs and systems will begin to form. The neural tube, which becomes the spinal cord and brain begins to form. It’s important that the mother intakes enough folic acid to prevent any defects from occurring in the neural tube. The eyes and ears are beginning to develop and tiny limb buds appear that will eventually develop into arms and legs. The embryo will have a heartbeat, but it is too faint to detect yet.
Weeks four through eight complete the embryonic stage. The embryo will continue developing and functioning all major body systems. It will start taking on a more human shape, although the head will be much larger proportionately to the rest of the body. The arms and legs will now be clearly visible. The mouth will be developing tooth buds which will eventually become baby teeth. The embryo’s facial features, such as eyes, nose, mouth and ears are all becoming more distinct. Fingers and toes will still be webbed and bones are beginning to develop. Around eight weeks, mothers often have their first ultrasound, where they will also get to hear the baby’s heartbeat using a doppler. After the eighth week, the embryo officially becomes a fetus.