Key takeaways
- In the first month, your baby is under 2 mm — about the size of a poppy seed.
- This is when fertilisation, implantation and the placenta begin; your baby's genetic makeup is already complete.
- The first sign is usually a missed period, sometimes with mild cramps, spotting, fatigue or breast tenderness.
- Start folic acid now, avoid alcohol and smoking, and book your first antenatal visit for 6–8 weeks.
In the first month of pregnancy (weeks 1–4), your baby is just a tiny cluster of rapidly dividing cells — smaller than 2 mm, about the size of a poppy seed — yet the foundations of the whole pregnancy are already being laid.
How big is the baby in the first month?
Your baby is under 2 mm, roughly the size of a poppy seed. At this stage it is called an embryo. Everything is microscopic, but growth is extraordinarily fast.
What is developing this month?
A remarkable amount happens in these first four weeks, even before many women realise they are pregnant:
- Fertilisation — the egg and sperm meet and combine
- Implantation — the embryo embeds into the lining of the womb
- The placenta begins to form to nourish your baby
- Your baby's genetic makeup is already complete, including whether it is a boy or girl
What symptoms can you expect in the first month?
The most common first sign is a missed period. Beyond that, early symptoms vary a lot — some women feel several, others feel nothing, and both are completely normal.
- A missed period
- Mild cramping
- Light implantation spotting
- Fatigue
- Breast tenderness
What should you do in the first month?
A few simple, well-timed steps give your pregnancy the healthiest possible start:
- Start folic acid straight away — it protects your baby's developing brain and spine. See our guide to folic acid in pregnancy.
- Confirm the pregnancy and read our guide on what to do after a positive test.
- Avoid alcohol, smoking and any medicine not approved by your doctor.
- Book your first antenatal visit for around 6 to 8 weeks.
Which tests or scans are done in the first month?
The first month is usually confirmed with a home urine pregnancy test. Your doctor may then start a few important early pregnancy blood tests:
- Beta-hCG — to confirm the pregnancy and monitor early hormone levels when needed
- Blood sugar — to check for and manage diabetes early in pregnancy
- Thyroid profile (TSH) — because thyroid problems can affect pregnancy and are easily treated
It is generally too early for an ultrasound — a dating scan is typically done a little later, around 6 to 8 weeks, at your first antenatal visit, along with baseline tests such as blood group and Rh typing, a complete blood count (CBC) and infection screening.