Your baby is the size of a poppy seed

4 Weeks Pregnant: Your Baby's Development

Congratulations! you're four weeks pregnant – you must have been tracking your cycle very closely to notice you may be pregnant after missing your period. A home pregnancy test should show a positive result, thanks to the hormone human chorionic gonadotrophin (hCG) that's released when you're pregnant. Whether you're completely thrilled about the prospect of becoming a new mum or you are still getting used to the idea, now is the time to start planning while treating yourself to some extra-special care. Even though you have just found out you're pregnant, the new life inside you has been busy. You released an egg two weeks after your last period, and around the three-week mark the fertilised egg moved down the fallopian tube towards your uterus, having divided into more than 100 cells, by which point it's known as an embryo. When you're four weeks pregnant, the embryo will have implanted itself into the side of your uterus. The cell layers in the embryo will grow into different parts of the developing fetus, such as the nervous system, skeleton, muscles, organs and skin. From 8 weeks after fertilisation onward, until birth, the embryo is known as a fetus. The placenta, a disk-like organ that connects your body's systems to that of the developing fetus, begins to form and attaches to the uterine wall where the blastocyst is implanted. The amniotic fluid, which will cushion the fetus throughout your pregnancy, is already forming inside an encircling membrane sac.

How Big Is Your Baby at 4 Weeks?

At four weeks, the newly implanted embryo is very tiny – just the size of a poppy seed. On average, it's about 2 millimetres long. For a sneak peek, take a look at this illustration to get a glimpse of what’s happening in your belly:

embryo at 4 weeks pregnant

Your Body at 4 Weeks Pregnant

This week, pregnancy symptoms may already be present. For example, you might feel some cramping and see a little spotting. That's not all: Here are some more early signs of pregnancy you may experience four weeks along.


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4 Weeks Pregnant: Your Symptoms

Some of the symptoms of early pregnancy may be very similar to getting your period. If you notice a missed period or you suspect you're pregnant, take a pregnancy test to be sure.

Keep in mind, every mum-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:

  • Bloating. You may be feeling a little bloated in the early days of pregnancy, for which you have your hormones to thank. The female hormone progesterone is doing its job to relax the muscles in your uterus so that it can expand as your little one grows over the nine months of pregnancy.

  • Light bleeding or spotting. It's common to see some spotting at four weeks – it's called implantation bleeding. If you see a lot of blood or if the spotting lasts longer than two days, it probably means you haven't missed your period at all, but if you did see a positive pregnancy test or you're concerned about anything, then see your GP.

  • Moodiness. Pregnancy hormones may make you feel emotional or upset. Now might be a great time to come up with some tactics for dealing with mood swings. Relaxation exercises, massage, sleep, and eating right are some of the easiest ways to deal with the issue.

  • Breast tenderness. Your breasts are starting to prepare for the important job of nourishing a new arrival. Hormones are surging, and your milk ducts are beginning to swell.

  • Morning sickness. You may or may not have morning sickness at four weeks pregnant. This symptom varies from one woman to the next, with some feeling only mildly nauseous and others vomiting. If it's affecting you, consider yourself in good company: some level of morning sickness impacts approximately 7 out of 10 women during their pregnancies. The good news is that this symptom usually subsides during the second trimester.

  • Light-coloured discharge. When you're four weeks pregnant, discharge is usually a normal symptom. It should be clear to milky coloured, with no real odour.

  • Fatigue. Don't be surprised if you feel completely exhausted, and get ready for even more tired days ahead. Your body is just getting used to the effort of building a brand-new person, and it can affect your energy levels. Fatigue can also arise from iron deficiency. More than 20 percent of pregnant women in Europe suffer from iron deficiency anaemia, so talk to your GP about your iron intake, as getting enough iron can help prevent anaemia.

4 Weeks Pregnant: Things to Consider

  • Find out when to expect your baby using our Due Date Calculator. A good estimate is 40 weeks after the first day of your last period. Remember that it's just an estimate, since most babies are born sometime between 38 and 42 weeks, with first-time mums often delivering a bit later than those who have already given birth.

  • Now is a good time to start a healthy diet if you haven't already.

  • Try to quit smoking and replace alcohol with water and other healthy beverages.

  • Avoid second-hand smoke. Recent research shows that exposure can increase the risk of complications including low birth weight, miscarriage, or ectopic pregnancy.

  • Try to relax and keep your stress levels low.

  • Keep on exercising if your doctor approves it. Most women can continue exercising throughout pregnancy as long as there are no complications. If you're not into exercise, ask your doctor whether you can start a simple routine that includes gentle activities like swimming, walking, or stretching. Labour and delivery are hard work – and the fitter you are, the better off you'll be.

  • Start taking prenatal vitamins every day – they'll support your health and help the new life inside you grow! The best ones contain at least 400 micrograms of folic acid, an important nutrient that's proven to reduce the likelihood of birth defects, along with vitamin D.

  • 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 paper 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

  • Plan an appointment with your Midwife or GP – your first appointment will probably be scheduled between 8 and 12 weeks of pregnancy as long as everything seems normal.

  • Call your doctor right away in case of heavy bleeding or pain other than mild cramping.

4 Weeks Pregnant: Your Checklist

  • Schedule your pregnancy confirmation appointment, if needed.

  • Share the good news with those closest to you – but remember, it’s best to wait until about 12 weeks before ‘going public’ with the baby news.

  • 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 National Health Service (NHS). The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.