There’s a lot going on in there as your baby begins to develop. Here’s more about what to expect, including your first trimester to-do checklist.
You may not look pregnant yet — but chances are you’re feeling it. That’s because a flood of pregnancy hormones is prepping your body to play baby hostess for the next nine months — so you could be in line for quite a few aches and pains, from fatigue to flatulence. While you might be less than thrilled with some of these symptoms, try to remind yourself that these temporary discomforts are part of the incredible process that’s happening inside: You’re growing a child!
How long is the first trimester?
The first trimester lasts from week 1 through the end of week 13 of pregnancy.
Not sure what week you are in your pregnancy? The first step to nailing your current week down is to calculate your due date. Keep in mind that your date might change (especially if you have irregular periods), so try to go with the flow.
Baby’s growth during the first trimester
During the first trimester alone your baby changes from a single fertilized cell (a zygote), to the embryo that implants itself in your uterine wall, to a peach-sized bundle of growing limbs and body systems. Organs take shape, and baby starts to move. Here are a few of the big highlights happening in this exciting time:
Baby’s bones: By about week 6, baby starts to sprout arms, legs, hands and feet — and fingers and toes around week 10.
Hair and nails: Skin begins forming between weeks 5 and 8, with hair follicles and nail beds forming around week 11.
Digestive system: By about week 8, baby’s intestines will begin forming, and your baby will have already gone through two sets of kidneys (with the third and final set on its way!).
Sense of touch: Your baby will have touch receptors on his face (mostly lips and nose) around week 8. By week 12, he’ll have receptors on his genitals, palms and the soles of his feet.
Eyesight: Optic nerves (which pass info from the eyes to the brain and back) and lenses begin to form by week 4, with the retina beginning to form around week 8.
Heart: By week 5, the tube that will become your baby’s heart begins to beat spontaneously. It will become stronger and more regular — and you’ll be able to hear it! — around week 9 or 10 (though sometimes later, depending on your baby’s position in your uterus).
Brain: By about week 8 of pregnancy, your baby’s brain will be wiggling his developing limbs.
Sense of taste: Your baby will have developed taste buds that connect to his brain by about week 8 — but he’ll need taste pores before he can taste the surrounding amniotic fluid (which, by the way, tastes like your most recent meal).
Other major first-trimester milestones include the formation of muscles, the production of white blood cells to fight off germs and the development of vocal cords.