Baby at 3 weeks

Implantation

Your developing blastocyst has travelled down the fallopian tube and is starting to implant itself in the lining of your uterus. At this time, 15 to 25 percent of women experience implantation bleeding, which is a light bleeding that happens about six to 12 days after conception. You may feel implantation cramps as well.

Early pregnancy symptoms

Some women may notice bloating, cramping, or spotting this week. Your breasts may also be more tender than usual and you may have a heightened sense of smell, one of the earliest pregnancy symptoms. So if your partner, your house, or your dog suddenly smells different to you, thank your surging hormones.

Baby at 4 weeks

Placenta and embryo begin forming

While you may have just started to wonder whether you’re pregnant, your soon-to-be baby has already found its home: The blastocyst has completed its journey from your fallopian tube to your uterus.

It making that unbreakable connection to you that’ll last the next eight months (and a lifetime after that).

As soon as that little ball of cells is settled in your uterus, it will undergo the great divide, splitting into two groups. Half of what’s now called the embryo will become your son or daughter, while the other half forms the placenta, your baby’s lifeline — which channels nutrients and carries waste away until delivery.

Baby at 5 weeks

Tiny embryo

Deep in your uterus an embryo is growing at a furious pace, and it looks more like a tadpole than a human. The embryo is made up of three layers – the ectoderm, the mesoderm, and the endoderm – which will later form all of the organs and tissues.

Brain development

Your baby’s brain, spinal cord, and nerves form from the neural tube, which is starting to develop from the embryo’s top layer which is called ectoderm. This layer will also give rise to skin, hair, nails, mammary and sweat glands, and tooth enamel.

Heart development

The heart and circulatory system begin to form in the embryo’s middle layer, or mesoderm. The mesoderm will also form your baby’s muscles, cartilage, bone, and the tissue under the skin.

Lungs and gut

The third layer, or endoderm, will become the lungs, intestines, and early urinary system, as well as the thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.

Baby at 6 weeks

An embryo with about the size and shape of a pea, some people think it resembles a tadpole with its little tail.

The arms and legs are starting to form and are known as limb buds. There are tiny dents where the ears will be.

There’s a bump where the heart is and another bulge where the head will be. Sometimes the heartbeat can be picked up by a vaginal ultrasound scan, but you are unlikely to be offered one unless you’ve had IVF.

The embryo is covered with a thin layer of transparent skin.