Deep in your uterus, your embryo is growing at a furious pace. At this point, he’s about the size of a sesame seed, and he looks more like a tiny tadpole than a human. He’s now made up of three layers — the ectoderm, the mesoderm, and the endoderm — which will later form all of his organs and tissues.
How is your baby growing?
The amniotic sac now houses the embryo, which floats in a sea of fluid. The embryo is the size of a sesame seed. The neutral tube will develop into your baby’s brain, spinal cord and nerves.
The neural tube — from which your baby’s brain, spinal cord, nerves, and backbone will sprout — is starting to develop in the top layer, called the ectoderm. This layer will also give rise to his skin, hair, nails, mammary and sweat glands, and tooth enamel.
His heart and circulatory system begin to form in the middle layer, or mesoderm. (This week, in fact, his tiny heart begins to divide into chambers and beat and pump blood.) The mesoderm will also form your baby’s muscles, cartilage, bone, and subcutaneous (under skin) tissue.
The third layer, or endoderm, will house his lungs, intestines, and rudimentary urinary system, as well as his thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.
What your baby looks like — 5 weeks
Bladder: You may soon start to notice a more frequent urge to pee. Your blood volume is increasing, creating a lot of extra fluid that ends up in your bladder.
Embryo: About the size of a sesame seed, the embryo is made of three layers of cells that are folded over on each other.
Neural tube: At the fold of the top layer of the embryo is the neural tube, which will develop into the baby’s brain, spinal cord, nerves, and backbone.
Primitive placenta: The tiny blood vessels (“villi”) that make up the primitive placenta deliver nourishment and oxygen to the embryo.
Yolk sac: The yolk sac will soon yield its job delivering nutrients to the developing placenta.
Amniotic sac: The amniotic sac now houses the embryo, which floats in a growing sea of amniotic fluid.
Tips of the week
- Start taking folic acid.
- Start taking prenatal vitamin supplements.
- Stop smoking and drinking alcohol.
- Stop or reduce caffeine intake.
- Eat a healthy balanced diet.