Things happen FAST.
The weirdest thing about your first week of pregnancy is that you're not actually pregnant yet. Your doctor considers Week 1 the week you started your last period — conception doesn't usually happen until two to three weeks after that, according to the Cleveland Clinic.
You're (still) not officially pregnant during Week 2, but during Week 3 it's on. If fertilization occurs, the embryo — at this point called a blastocyst — attaches itself to the wall of your uterus.
Your baby — which is now a little group of cells — is now about the size of a poppy seed. Around this time, the embryo splits in two. One part becomes the placenta and the other continues to grow into a tiny human.
Ready for some magic? At only five weeks along, your baby's heart is beating steadily. The level of a pregnancy hormone called hCG in your bloodstream will also spike right about now, causing all the early pregnancy signs you probably aren't so excited about.
RELATED: 7 Things Spotting During Pregnancy Could Mean
Your baby is now the size of a pomegranate seed or sweet pea. During your sixth week of pregnancy, his or her heart is also humming along at 150 beats per minute and facial features are beginning to take shape.
At this stage, your baby's brain is growing quickly and his or her facial features are starting to become even more recognizable. Even the arms and legs are growing, allowing the little one to move around a little bit.
Now that you're eight weeks along, your baby is about the size of a raspberry. His or her brain is more complex and the embryonic tail is disappearing. Down the road, that tail actually becomes the tailbone.
It's still too early to tell your baby's sex, but external reproductive organs are beginning to form. All of the other body parts are now present, too — they just have a lot more growing to do.
RELATED: 8 Reasons Why Your Pregnancy Test Could Be Showing the Wrong Result
At Week 10, your baby's hip and shoulder joints are able to rotate, giving much more flexibility and freedom to kick around. Fingers and toes will also start to grow.
Your baby starts to breathe amniotic fluid and begins forming a skeleton. By week 13, he or she is about the size of a lemon.
Your baby starts making faces — including cute little squints and frowns — as facial muscles start to twitch and flex. By your 16th week of pregnancy, it can suck its thumb and straighten its spine.
All that talking to your baby through your belly is starting to pay off. Your little one can officially hear you, and because of that he or she will instantly recognize your voice after birth.
RELATED: 16 Celebrities Who Hid Their Pregnancies On Screen
Let the kicks begin! Around week 20, you'll probably start to feel your baby kick. You'll also probably have your second trimester ultrasound, which is when you'll be able to find out for sure whether you're having a boy or girl.
Now the size of an eggplant, your baby has started opening and closing his or her eyes. Up until this point, the eyelids have been fused shut.
Around week 37, your little one is receiving all sorts of antibodies via the umbilical cord, and your doctor will begin checking for signs of labor. Make sure your hospital go bag is ready: Your baby could make an entrance within a few hours or a few weeks.