The browser you are using is too old for our website. Please visit from Chrome and you will be able to browse normally.


      1-4 weeks pregnant

      First Weeks Of Pregnancy

      1-4 weeks pregnant

      Life begins

      Although you may not even know you’re pregnant, by week 4 your body is already going through some significant changes. Learn when your baby’s genetic make-up becomes set and how your placenta will soon begin to form to support them, along with nutrition tips for weeks 1–4 of pregnancy.

      Pregnancy Weeks 1 4

      Your baby's development at 1-4 weeks

      The start of your baby’s journey

      Fertilisation takes place around 14 days after the start of your last period. At that point, the fertilised egg that will eventually become your baby is technically called a zygote.

      During the 90 hours after fertilisation, the cells divide and subdivide into a pinhead-sized solid mass of cells that gradually makes the journey from your fallopian tube to your uterus.

      Around 6-10 days after ovulation you may notice some light spotting as the bundle of cells, now known as a blastocyst, attaches to the wall of your womb.

      Because of the way pregnancy is measured, you are considered to be 2 weeks pregnant at the time of fertilisation.

      Whether you’re aware of any subtle changes or not, your baby, now known as an embryo, already has the basic building blocks of their body in place. The rapidly multiplying cells form distinct layers within the embryo. These will soon become your baby’s internal organs; the skeleton and muscles; brain; nervous system; and external body parts, such as skin, eye lenses and nails.

      Even though there are incredible developments taking place, at 4 weeks, or 2 weeks after fertilisation, the only sign of pregnancy may be the lack of your usual premenstrual symptoms.

      The placenta: Building a super organ

      In the 4th week of pregnancy, your baby is receiving all the nourishment they need from a tiny yolk sac. But very soon your placenta will begin to form. This life-sustaining organ will supply your baby with the oxygen and nutrients they need to grow and develop. It also passes antibodies to your baby, which will provide essential resistance to infection throughout pregnancy.

      Another function of the placenta is hormone production. These hormones help your baby grow and develop while supporting your own physical changes from the earliest stages of pregnancy. Progesterone and relaxin, for example, both have a relaxant effect on your muscles, allowing your uterus to adapt and make room for your growing baby.

      Vitamin C: Supporting healthy cells for life

      Vitamin C is a vital nutrient to include in your balanced diet in the first 4 weeks of pregnancy. As your body adjusts and prepares to support your baby, it plays an important role in keeping cells healthy and contributes to normal collagen function. Collagen gives support and structure to tissue and organs such as skin, blood vessels and cartilage, and is one of the building blocks of your rapidly growing placenta.

      A balanced diet containing fruit and vegetables can provide all the vitamin C you need in pregnancy.

      The Recommended Dietary Allowance (RDA) of vitamin C during pregnancy is 80mg a day. A large strawberry provides around 10mg.

      An equally important role of vitamin C is to aid the absorption of non-haem iron (the iron found in plant sources such as spinach) into your bloodstream. Iron is a key component of your blood, helping to transport oxygen around your body and to your baby. A healthy supply of this mineral is essential for your baby’s normal cognitive function.


      Add one of the following vitamin C-rich foods to your mealtimes to increase your absorption of iron from plant sources such as green, leafy vegetables:

      • Steamed broccoli
      • Raw spinach
      • Tomatoes
      • Strawberries
      • Brussels sprouts
      • A kiwi fruit
      • Blueberries
      • Freshly squeezed fruit juice
      • A squeeze of lemon or lime

      Your baby, this week

      Discover the science behind your baby's developments, week-by-week

      Join now for free

      Related articles

      Questions about feeding and nutrition?

      Our nutritionists and feeding advisors are always on hand to talk about feeding your baby. So if you have a question, just get in touch.

      Your baby, this week

      Discover the science behind your baby's developments, week-by-week

      Join now for free

      Your privacy is important to us and therefore we would like to explain how we use cookies on this website. With your consent, we will use cookies to measure and analyse how our website is used (analytical cookies), to tailor it to your interests (personalisation cookies), and to show you relevant advertising and information (targeting cookies) we think you will like. For more information please read the cookie statement.

      Privacy Settings

      You can choose your preferences anytime for cookies and tracking. For more information please read our cookie policy.

      • Strictly necessary

        They are necessary for the website to function and cannot be switched off. They are usually only set in response to actions made by you which amount to a request for services (setting your privacy preferences, logging in, filling in forms, etc.). You can set your browser to block or alert you about these cookies, but some parts of the site will not then work.

      • Analytical cookies

        They allow us to count visits and traffic sources, to measure and improve the performance of our site. They show us which pages are the most and least popular and how visitors move around the site. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.

      • Personalisation cookies

        They enable website’s enhanced functionality and personalization. They may be set by us or by third parties whose services we have added to our pages. If you do not allow these cookies, some or all of these services may not function properly.

      • Targeting cookies

        They may be set through our site by our advertising partners, to build a profile of your interests and to show you relevant adverts on other sites. They do not store directly personal information, but are based on uniquely identifying your browser and internet device. If you do not allow these cookies, you will experience less targeted advertising.