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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!

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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, the size of a poppy seed.

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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, 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.

That's not all: Here are more early signs of pregnancy, four weeks along.

pregnancy week 4 fetus

4 Weeks Pregnant: Your symptoms

  • 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, and the swelling means your womb is taking up more space than usual. Test your knowledge of the early signs of pregnancy in our poll, and read on for more.

  • 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 level 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-colored discharge. When you’re four weeks pregnant, increased vaginal discharge is normal. It should be sticky, clear, or white. If you notice a bad odor 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 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.

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. Labor 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.

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?

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.

Start eating a healthy diet and taking prenatal vitamins.

Sign up for even more weekly pregnancy tips:

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.

Start eating a healthy diet and taking prenatal vitamins.

Sign up to get weekly pregnancy tips

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