The bulge at the lower part of this image will eventually become the baby's head. Segments called somites (seen as bright, round areas running down one side of the embryo), which will form the baby's spine, have started to develop.
At this important stage of development, the building blocks of your baby's spine are being laid down.
By the end of this 5th week, individual elements that will form the embryo have begun to develop.
Starting at what will become the head end, individual segments, called "somites," form. Roughly three new pairs of somites appear every day and each forms part of your baby's spine as well as the muscles associated with each segment of the body. Eventually there will be four somites at the head, eight in the region of the neck, 12 at chest level, five in the lumbar region, and five in the pelvic area.
More somites develop in the baby below the pelvis but most disappear. In other mammals, these develop to form the tail.
Focus On... Your body
Regular exercise will increase your base metabolic rate, which is the rate at which your body burns calories. During pregnancy your metabolism will already be slightly elevated. When exercising your body will be encouraged to use up excess energy and fat reserves, but will always keep enough reserve energy to facilitate the growth of your baby.
Exercise will also help your body regulate blood sugar (see Get carb loading) and energy levels.
Doing moderate aerobic exercise during pregnancy – such as walking or running – regularly will burn excess fat, but won't affect your baby's development.
Ask A... Nutritionist
I'm underweight. Could this affect my pregnancy?
You may be more likely to suffer from nutritional deficiencies, which could affect the baby's health; you are also more likely to give birth prematurely, and have a smaller-than-usual baby, who is more vulnerable to health problems.
To gain weight, eat bigger portions and choose healthy foods that have plenty of protein, good-quality fats, and unrefined carbohydrates (see Get carb loading). Opt for nutrient- and calorie-dense foods, such as avocados and whole-milk dairy products; eat lots of leafy greens to ensure you are getting key vitamins and minerals (see Vitamins and minerals). Eat healthy snacks, such as nuts, fruit, and seeds, and don't skip breakfast. Your doctor will refer you to a dietician, if necessary.