Pregnancy Week 4

At 4 weeks pregnant, the embryo is settling into the lining of your uterus. This process is called implantation, and it marks the start of your body and the embryo working closely together to support the pregnancy.

Your baby is still incredibly tiny - around 0.2–0.3mm, smaller than a poppy seed at the start of the week, but growing quickly. At this stage, it is made up of rapidly dividing cells, but the foundations for pregnancy are already beginning to appear.

The amniotic sac is starting to form. This will eventually hold the amniotic fluid that cushions and protects your baby. The yolk sac is also developing. In these very early weeks, it helps provide nourishment before the placenta fully takes over.

A very early version of the umbilical cord, sometimes called the umbilical stalk, is beginning to appear too. These structures are tiny, but they are part of the early support system your baby will rely on as development continues.

This is a rapid, delicate stage of development, even though there is still nothing visible from the outside. Over the next few days and weeks, the early pregnancy structures will continue to grow and specialise.

Week 4 is often the point when you first suspect you might be pregnant. Your period may be late, or you may be noticing early symptoms such as sore breasts, tiredness, a heightened sense of smell, needing to wee more often, mild nausea, changes in taste, or a milky white vaginal discharge.

Some people have several symptoms by now. Others feel completely normal. Both can happen.

A home pregnancy test may show a positive result around the time your period is due, because your body is producing hCG, the pregnancy hormone that tests detect. If you test very early and get a negative result, but your period still does not arrive, try testing again in a few days.

Light spotting can sometimes happen in early pregnancy, including around implantation. However, you should get medical advice if you have vaginal bleeding, pain, or symptoms that worry you, as bleeding in pregnancy can sometimes need urgent assessment.

Emotionally, Week 4 can feel like a crossroads. You may be waiting to test, staring at a faint line, trying to work out dates, or wondering whether every twinge means something.

If you have been trying for a baby, you might feel thrilled but nervous. If this pregnancy is unexpected, you might feel overwhelmed or unsure what to do next. If you have experienced loss before, you may find it hard to relax into the news.

There is no "right" emotional response to early pregnancy. It can take time for the news to feel real, especially when the pregnancy is still so new.

If you do tell someone this week, choose someone who will respond in the way you need - whether that is excitement, calm reassurance, practical help, or just a good cup of tea and a listening ear.

If your period is late, take a home pregnancy test. If it is positive, you can usually self-refer to your local NHS maternity service, or contact your GP surgery if you are not sure how it works in your area.

If you are not already taking folic acid, start now. Other first steps include:

At 4 weeks, the most useful first steps are confirming the pregnancy, starting or continuing folic acid, and finding out how to access maternity care. You do not need to make every decision at once.