§first trimester · week 3 of 40
you're 3 weeks pregnant.
last revised · baby is about 0.06 cm (0.02") · 0.02 g (0.00 oz)
about the size of a sugar.
A cluster of cells (the morula and then blastocyst) is drifting through the fallopian tube on its way to the uterus.
this week's highlights
- Rapid cell division
- Blastocyst forms
- Heading to the uterus
- Inner cell mass appears
how your baby looks
A hollow ball of about 100 cells called a blastocyst. The inner cells will become the embryo; the outer cells will become the placenta.
body in focus
- head
- body
- A hollow ball of about 100 cells, split between future embryo and future placenta.
- hands
- feet
what's happening in your body
Hormones are quietly shifting. A few people notice a slight twinge during implantation late in week 3, but most feel nothing yet.
gentle tips
- Stay hydrated — your blood volume is starting to ramp up.
- Skip any new medications without checking with your doctor first.
- Avoid raw fish, unpasteurized dairy, and undercooked meat from now on.
- Note the date of your last period — you'll need it for due-date math.
what to expect next
By the end of next week the blastocyst burrows into the uterine wall — implantation. Some women notice light spotting then.