Around the five-week mark, your baby's heart will begin to beat.

At 27 weeks, they'll have regular sleep and wake cycles.

And at 39 weeks, your baby will be physically developed.

Use this timeline to learn how your baby is developing throughout the pregnancy.

For the first few weeks of what is counted as your pregnancy, you're not pregnant yet.

This is the time between the first day of your last period and when you ovulate and conceive.

Over the next several days, the fertilized egg will start dividing into multiple cells as it travels down the fallopian tube, enters your uterus, and burrows into the uterine lining.

You're now about four weeks from the beginning of your last period.

This ball of cells, called a blastocyst, has begun to produce the pregnancy hormone HCG.

This hormone tells your ovaries to stop releasing eggs and can be detected by a pregnancy test.

A mere 16 days after conception, your fetus's neural plate forms.

Think of it as the foundation of your baby's brain and spinal cord.

The neural plate folds onto itself to form the neural tube, which closes by about week six of pregnancy to eventually become the brain and spinal cord.

Folic acid is one of the B vitamins that help form this neural tube.

Because your baby's nervous system starts developing right out of the gate, it's important to consume 400 micrograms of folic acid daily before getting pregnant, and up that amount to 600 micrograms once you do.

This can reduce certain defects of the brain and spinal cord by more than 70%.

At two months pregnant, the cluster of cells that will become your baby's heart has begun to develop and pulse.

Your baby's face and buds, which will eventually be limbs, begin to develop.

Organs such as the brain, sensory organs, and the digestive tract begin to take shape.

Your baby has what looks like a little tail.

It will recede after a few weeks and form the tailbone.

At three months pregnant, the embryo already has a human appearance.

The limbs, hands, feet, fingers, and toes are recognizable.

Their skin is so thin that you can see the blood vessels beneath it.

Though reproductive organs have begun to form, they can't yet be determined on an ultrasound or sonogram.

By the end of the third month, your baby is fully formed.

They weigh about an ounce and are four inches long.

Since your baby's most critical development has occurred, your chance of miscarriage drops considerably after three months into the pregnancy.

During the second trimester, very fine wisps of hair appear on your baby's body.

This is called lanugo and plays a critical role in protecting the fetus from damaging substances found in amniotic fluid.

Your baby's senses—smell, vision, touch, taste, and hearing—are developing, and they may be able to hear your voice.

Your baby's eyelids are still fused shut, but they can sense light.

If you shine a flashlight on your tummy, they'll move away from the beam.

Their movements have gone from flutters to full-on kicks and jabs against the walls of your womb.

Ultrasounds done at four months pregnant may reveal your baby's sex.

Here you are in your seventh month of pregnancy.

You've come a long way.

During the third trimester, your fetus continues to grow in size and weight.

Your baby's lungs are beginning to reach maturity, meaning your baby would have a good chance of surviving if born now.

Starting in week 36, your baby gains about half a pound and grows half an inch a week.

Many babies turn head down and stay in that position until birth.

Thank you for watching this video.

Please watch my other videos if you would like to know what to expect during a vaginal delivery or c-section.