Week 4

Welcome to the beginning of the embryo stage. Your baby is still way too teeny to be seen or called a fetus yet, and is no longer than 1mm - about the size of a poppy seed. It’s now implantation time – the blastocyst will begin burrowing into your uterine lining, before splitting to form the placenta and the embryo.

What’s my baby doing at four weeks pregnant?

Your soon-to-be-baby has found its new home, where it will now grow for the next eight months. It’s completed the journey from the fallopian tube to your uterus and has inserted itself into the lining of your womb. Some women swear they can feel this happening, and report a cramping style sensation, whereas others say they had light spotting.

As soon as that precious ball of cells has settled into its new home, it will begin splitting in two. One half is now called the embryo and will become your baby, the other half will become the placenta, which will act as your growing baby’s lifeline for the next eight months.

This week, the amniotic sac will form around it and there are three distinctive layers of cells that will grow into different parts of your baby’s body.

Your embryo might be tiny, but it’s busy! This week, the amniotic sac will form around it and there are three distinctive layers of cells that will grow into different parts of your baby’s body. The endoderm is the inner layer – think digestive system, liver and lungs. The mesoderm is the middle layer, and will become your baby’s heart, sex organs, bones, kidneys and muscles. And the ectoderm is the outer layer – this will form your baby’s skin, hair and eyes.

What’s my body doing at four weeks pregnant?

If you took a blood pregnancy test around this week it would be positive (for a urine pregnancy test, it might be a few days too soon). That said, your body knows it is pregnant and is getting ready, big time! Some women will be completely oblivious to their growing baby at this stage, others will experience some early pregnancy symptoms such as mood swings, bloating and cramping.

As the blastocyst begin to attach to your womb, around 30% of women might experience some implantation bleeding. Midwife Lesley Gilchrist explains, ‘it’s extremely easy to mistake implantation bleeding for an early period as man of the pre-menstrual symptoms, such as cramps, bloating and mood changes are present with pregnancy too. The difference with a period and an implantation bleed is the length of the bleeding, the colour of the bloody loss and the heaviness of the blood flow. Implantation bleeding is not a sign that there is anything wrong with the pregnancy and there are no links to implantation bleeding and miscarriage.’

Within six to twelve days after fertilisation, your body starts releasing hCG – human chorionic gonadotropin. This is the pregnancy hormone that makes that extra line appear on your pregnancy test. Whilst we’re talking about pregnancy tests, it’s important to note, it can take over a week for your body to start producing enough pregnancy hormones to be detected. If you’ve missed a period and had a negative test, it’s worth doing another one in a week’s time.

What are the common symptoms to look out for at four weeks?

•        Implantation bleeding: As we mentioned above, if you find you’re having a really light period a week before you’re due, or spotting slightly, this could be an implantation bleed. Only a small percentage of women experience an implantation bleed, so do not worry either way.

•        Period-like symptoms: Your hormones are going mad, which can cause everything from bloating and cramping to mood swings.

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