Your baby is the size of a poppy seed

4 Weeks Pregnant: Your Baby's Development

Congratulations if you've just found out you are pregnant! You may have discovered this after having missed your period. At four weeks pregnant, a home pregnancy test could show a positive result if it detects the pregnancy hormone hCG (human chorionic gonadotropin), which is present in your urine about 10 days after conception. Whether you’re completely thrilled about the prospect of becoming a parent, or are still getting used to the idea, now is the time to start planning while treating yourself to some extra-special care. If you're wondering when to expect your little one, try our Due Date Calculator to find out! At four weeks pregnant, it may also be possible for your healthcare provider to perform an ultrasound exam to help calculate your due date. While you’ve been adjusting to being pregnant, the new life inside you has been busy. The fertilized egg is implanting itself into the side of your uterus. It rapidly divides into layers of cells, some of which become the embryo. The cell layers will start to grow into different parts of your little one's body, such as the nervous system, skeleton, muscles, organs, and skin. The placenta, a disk-like organ that connects your body’s systems to that of the baby, begins to form and attaches to the uterine wall where the egg is implanted. The umbilical cord will eventually come out of one side of the placenta, and the amniotic fluid, which will cushion your baby throughout your pregnancy, is already forming inside a surrounding membrane, or yolk sac. During the upcoming weeks, your little one will form a neural tube, which is the main building block for the brain and spine.

How Big Is Your Baby at 4 Weeks?

The newly implanted embryo is very tiny — only about 0.04 inch long (about 0.1 centimetres), the size of a poppy seed. For a sneak peek, take a look at this illustration to get a glimpse of what’s happening in your belly:

Embryo development at 4 weeks pregnant
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Mom's Body at 4 Weeks Pregnant

This week, a few pregnancy symptoms may appear, though some moms-to-be won't have noticed any signs yet. You might feel some cramping and see a little bit of spotting at four weeks pregnant, both of which can happen as the fertilized egg implants itself in your uterus. Your body is now starting to make the pregnancy hormone hCG. This hormone tells your ovaries to stop releasing an egg each month, thus stopping your monthly period, and it also increases the production of other hormones, such as estrogen and progesterone. If you've taken a home pregnancy test and gotten a positive result, that's because these tests are designed to detect levels of hCG in your urine.

4 Weeks Pregnant: Your Symptoms

Every mom-to-be’s experience of pregnancy is unique. In fact, what you experience during this pregnancy may be different to what you experienced during a previous pregnancy. To help you feel more prepared for whatever may come, take a look at this list of possible symptoms of pregnancy at four weeks:

  • Bloated stomach. Your body is preparing itself to house a rapidly growing baby for the next several months. Expect a bit of bloating, particularly in your abdomen. Your uterine lining is getting a bit thicker at four weeks pregnant, and the swelling means your womb is taking up more space in your belly than usual. Learn more about some of the early signs of pregnancy.

  • Light bleeding or spotting. Some women have some spotting at four weeks pregnant — it’s called implantation bleeding. If you see a lot of blood, if the spotting lasts longer than two days, or you have any concerns, see your doctor right away.

  • Moodiness. Other symptoms you might notice at four weeks pregnant include mood swings. Triggered by increasing hormone levels, these extreme emotions and wild shifts may be the strongest in the first and the third trimesters. Relaxation exercises, massages, sleep, and following a balanced diet are some of the easiest ways to help yourself feel better.

  • Breast tenderness. Just like your abdomen, your breasts are starting to prepare for the important job of nourishing a new arrival. The number of milk glands increases, and the fat layer also thickens, causing your breasts to become enlarged.

  • Morning sickness. You may or may not have morning sickness — a queasiness that may strike at any time of day, not just in the morning — at four weeks pregnant. This condition varies from one woman to the next, with some feeling only mildly nauseated and others vomiting. If it’s affecting you, consider yourself in good company: Some degree of morning sickness impacts approximately 85 percent of women during their pregnancies. The good news is these unpleasant symptoms often subside during the second trimester.

  • Light-coloured discharge. When you’re four weeks pregnant, increased vaginal discharge is normal. It should be sticky, clear, or white. If you notice a bad odour or have a sore or itchy vaginal area, speak to your healthcare provider.

  • Fatigue. Don’t be surprised if you feel completely exhausted, and get ready for even more tired days ahead. Your body is working round the clock to support your little one, and your levels of the hormone progesterone are increasing, which can tire you out. Fatigue is a normal part of pregnancy, but it can also be a sign of an iron deficiency, so you may want to talk to your healthcare provider about your iron intake. Getting enough can help prevent anemia, which can lead to feelings of lethargy.

  • No symptoms. Of course, it’s also possible that you’ll have no symptoms at four weeks pregnant. Some moms-to-be don’t notice any symptoms of pregnancy until one or two weeks after their missed period, and sometimes even later.

4 Weeks Pregnant: Things to Consider

  • Now is a good time to start a healthy eating plan, if you haven’t already. Make sure you're including iron-rich foods like spinach and cereals to prevent anemia, as well as calcium from milk, cheese, and yogurt to help your growing baby build strong bones.

  • Stop unhealthy habits right away. Quit smoking and replace alcohol with water and other healthy beverages to help prevent preterm birth and other birth defects.

  • Avoid secondhand smoke. Recent research shows exposure can increase the risk of complications such as low birth weight, miscarriage, and ectopic pregnancy.

  • Try to relax and keep your stress level low.

  • Keep on exercising if your doctor approves. Most women can continue exercising throughout pregnancy, as long as there are no complications. If you haven't been exercising before, consider asking your doctor whether you can start a simple routine that includes gentle activities like swimming, walking, and stretching. Labour and delivery are hard work, and the fitter you are, the better off you’ll be.

  • Start taking prenatal vitamins every day to support your health and help the new life inside you grow! Look for a vitamin that contains at least 400 micrograms (mcg) of folic acid, an important nutrient that’s proven to reduce the likelihood of birth defects.

  • Download our Pregnancy Guide for even more information to help get you through the coming months, including info on nutrition, prenatal visits, and more.

  • Research the kind of healthcare provider you'd like to work with during your pregnancy, if you don’t already have one in mind.

  • Start a memory book. If you’d like to document your pregnancy as a keepsake for your child, you might like to buy one now. You can order one online, buy one at your local big box store, or create your own using a hard-cover notebook. Add pictures of your bump week to week to see the progress that will eventually be happening. Note down special dates like the date you found out you were pregnant and the date you first feel a flutter of movement. You might even like to write a letter to your child that he can read in the years to come. It could also be fun to write down your predictions about eye colour and hair colour and see if you got it right in a few years’ time.

4 Weeks Pregnant: Ask Your Doctor

  • Are there any specific tests you may need based on your ethnicity or medical history?

  • How can you safely continue (or discontinue) using certain medications you may already be taking once you find out you're pregnant?

  • When will the routine pregnancy checkups and tests be, and how do you go about scheduling them?

4 Weeks Pregnant: Your Checklist

  • Schedule a pregnancy confirmation appointment, if needed.

  • Share the good news with your partner, and maybe a few close family members and friends.

  • Think about what lifestyle changes you may need to make (like adjusting your diet, for example), and plan how you will implement them.

  • Sign up for even more weekly pregnancy tips:

How we wrote this article
The information in this article is based on the expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.