What your baby looks like — 4 weeks
Amniotic sac: By next week, this cavity will envelop the embryo and continue to house your baby throughout your pregnancy.
Embryo: All of your baby’s organs and body parts will develop from the two layers of cells that now make up the embryo: the epiblast and the hypoblast.
How your baby’s growing
This week marks the beginning of the embryonic period. From now until 10 weeks, all of your baby’s organs will begin to develop and some will even begin to function. As a result, this is the time when she’ll be most vulnerable to anything that might interfere with her development.
Right now your baby is an embryo the size of a poppy seed, consisting of two layers: the epiblast and the hypoblast, from which all of her organs and body parts will develop.
The primitive placenta is also made up of two layers at this point. Its cells are tunneling into the lining of your uterus, creating spaces for your blood to flow so that the developed placenta will be able to provide nutrients and oxygen to your growing baby when it starts to function at the end of this week.
Also present now are the amniotic sac, which will house your baby; the amniotic fluid, which will cushion her as she grows; and the yolk sac, which produces your baby’s red blood cells and helps deliver nutrients to her until the placenta has developed and is ready to take over this duty.
What should I plan?
- Perform a urine pregnancy test. If is it negative you could either wait for another week and ask your doctor to do a blood test to detect the pregnancy hormone called B-HCG.
- You should already be taking a multivitamin that contains at least 400 micrograms (mcg) of folic acid. Once you’re pregnant, you’ll need a bit more — 600 mcg a day — so switch to a prenatal vitamin if you haven’t already.