Your baby's rapid growth continues and she'll nearly double in size from 2.25 in (5.5 cm) to 4 in (10 cm) during the next three weeks. Muscle and bone growth advances, but, although all joints are present, it will be three weeks before the skeleton begins to harden.
Your baby is now totally dependent on the placenta for her nourishment. Environmental factors have almost no influence on your baby's size at this stage; all babies up until around 20 weeks' gestation are the same size.
The placenta is larger than your baby and supplies all the nutrients she needs. To aid her growth, the placenta extracts amino acids from your circulation, giving her high levels. Amino acids are the building blocks of protein, from which muscles and organs develop.
The umbilical cord can be seen connecting this 13-week-old fetus with the placenta, which nourishes your baby. The incredible blood vessels of the placenta are clearly visible in the background.
Protein is required for the development of the baby and placenta, as well as to fuel changes taking place in your body (see Protein). The protein requirement for pregnancy is 6 or 6.5 oz daily, instead of the usual 5 or 5.5 oz. Include a source in all three meals daily. Protein sources include meat, poultry, fish, milk, cheese, beans, nuts, and seeds.
The best protein foods are those that are lower in saturated fat and cholesterol. Trim the fat off meat and eat one or two servings of fish or seafood. When choosing dairy products, pick skim milk and low-fat cheeses. These retain all the protein benefits of the whole milk versions. Nuts and seeds are rich in heart-healthy oils. Vegetarians need to eat a wide range of plant proteins to ensure they are getting adequate amino acids (see Vegetarian mom-to-be).
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