Week 5 starts with the ongoing development of the internal organs, including the central nervous system and the heart. New features that make the embryo more baby like start to develop. Important processes of the brain and central nervous system begin to develop during this stage. Week 5 is usually the first week a pregnant mother will obtain an ultrasound because it gives the doctors a better idea of the gestation period and allows for early detection of abnormalities. Week five is usually the week that some mothers discover that they are carrying multiples.  

What is Developing?

During the fifth week the mandibular process forms and the midbrain forms. The mandibular process is specific to embryo development and aids development of lower jaw features, mainly how the jaw will attach to the skull. The midbrain is the part of the brain that helps regulate temperature, hearing, vision, and motor control. The midbrain is one of the most critical elements of the central nervous system. The head continues to become rounder. The little nubs for the limbs start to elongate. The arms at this stage are called forelimbs and the legs at this stage are called hindlimbs. Along with the midbrain, the external acoustic meatus grows. This structure is a part of the ear and is imperative for hearing.

The eyes and ears start to grow and the embryo still has its tail. A common fact that most people don’t know is that in the early stages of development, the embryo has a tail. Scientist think that millions of years ago, humans might have had tail like appendages. However, due to evolution the human tail wasn’t needed anymore. The tail only forms during the first few weeks of pregnancy before disappearing. The wrists and small nub like fingers are developing during this stage.  

What to Expect from the Ultrasound?

This will be the first week that the mother will be able to observe the heartbeat. Usually an endovaginal ultrasound is conducted. This type of ultrasound resembles the normal pelvic exams except that a wand is inserted into the vagina to allow a more accurate ultrasound. This procedure is relatively painless and you don’t have to have a full urinary bladder to get an accurate reading. However, a full urinary bladder will help elevate the mother’s womb, allowing for a better quality picture. During this ultrasound, the doctor will be able to conclude if there is more than one baby present. Before the fifth week, the embryo was too small to conclude such details. Week 5 sees the start of a more developed embryo that can be measured. The doctor will check for any irregularities with the developing embryo. This is important for mothers that are expecting multiples or that have had issues with previous pregnancies. The placenta should start developing by week 5 and the mother should be able to see the slight distinction between the placenta and the embryo. A week 5 ultrasound will allow the doctor to determine a more accurate due date based on embryo development and size.