4 Weeks Pregnant

Jan 28, 2022 | 3 Minute Read

It's implantation time! This week the embryo, which is now called a blastocyst, has found its way to the uterus, and is looking for a suitable place to nestle in for the next 36 weeks or so. Implantation usually happens at around the time you would be expecting your period so many women aren’t surprised when they have a slight bleed in the 4th week. But, if it's only slight spotting it could be an implantation bleed and not a regular period. The uterine wall is so engorged with blood at this stage that any disruption can cause a light bleed. Some women say they can feel the moment when the blastocyst embeds, and who can say they are wrong?

Can I get excited yet?

You are likely to suspect that you could be pregnant if your period doesn’t come this week when you expect it to. Keeping track of your cycles with a calendar is a good idea. You may be experiencing some early pregnancy symptoms (see below) which alert you that your body feels a little different from how it usually feels. Don’t be concerned if you feel the same as you normally do though. Even if you are officially 4 weeks pregnant, your body is still getting accustomed to pregnancy changes. By the time you are 4 weeks pregnant it's possible to confirm your pregnancy with a blood or urine test. Both are extremely sensitive to detecting Human Chorionic Gonadotrophin Hormone (HCG) if it's present in your system. You can test your own urine for HCG in the privacy of your own home and the best time to do this is when you wake up in the morning. This is when the concentration of HCG will be at its highest.

Your physical changes this week

You may feel some lower pelvic cramping and a sensation of "fullness". You may feel bloated or have more gas than you usually do.

You could start to feel some nausea, or morning sickness, especially if you haven t eaten for a while. The smell or thought of some foods may turn you off, even if you usually love them. Coffee, fish, red meat and even pet food can be enough to make you feel you want to vomit.

Your breasts may be tender and your nipples more sensitive. Your breasts may even look fuller and more rounded, especially if your breasts are usually a small size.

You may want to go to the toilet to pee more often. You don’t seem to be able to hold on for as long as you usually do and only can pee small amounts. This is because of the increase in your blood volume and the pressure of your full uterus pressing down on your bladder underneath.

You may have some slight spotting from an implantation bleed.

Your emotional changes this week

You may be feeling a big sense of apprehension and excitement. Waiting to see if your period starts can seem like an eternity, with frequent trips to the bathroom to check.

You may feel like you usually do before you have a period. A little more emotional, easily irritated and generally feeling more moody.

If you want to conceive, but have a negative pregnancy test, you may be feeling disappointed with the result. Talk with your partner or a supportive friend. Alternately, if you didn’t plan on getting pregnant, but find out that you are, this can be a stressful time.

Your baby's changes this week

This week your baby is the size of a poppy seed. It is still barely visible to the naked eye.

In the 4th week of pregnancy there is a lot of organization and cell separation going on. Three distinct layers of cells start to form. The ectoderm (outer layer), will eventually become the baby's skin, eyes, hair, their nervous system, their brain, and even the enamel of their teeth. The middle layer (mesoderm) will become their skeleton, muscles and kidneys, tissues and vascular (blood) system. The layer on the inside (endoderm) will eventually become their internal organs.

Once a cell has a specific function, it can’t become a different type of cell. Every cell is pre-programmed from the start and knows what to do and what it will become.

Hints for the week

Buy a pregnancy test or two from the drug store or supermarket. The most expensive is not necessarily the best. Try to choose one which has 2 sticks so you can repeat the test. It is impossible to get a false positive reading, though in the very early stages you can get a false negative result. Keep the test - if it is positive it is a nice memento to hold on to.

Make the first prenatal appointment with your pregnancy care provider for ongoing prenatal care.

Avoid getting overheated and try to stay healthy. An elevated temperature in the early weeks of pregnancy can sometimes carry a risk to the baby as it is forming.

Now we move onto week 5, when your baby is growing and getting comfortable.

For more information see Pregnancy or Week by Week.

The information of this article has been reviewed by nursing experts of the Association of Women’s Health, Obstetric, & Neonatal Nurses (AWHONN). The content should not substitute medical advice from your personal healthcare provider. Please consult your healthcare provider for recommendations/diagnosis or treatment. For more advice from AWHONN nurses, visit Healthy Mom&Baby at health4mom.org.