Trimester 1
Week 3
Your baby is about the size of a poppy seed.
Length: 0.1 cm · Weight: <1 g
Common this week: Light spotting, Mild cramping, Bloating.
Baby development
- Fertilisation occurs — a sperm meets the egg to form a single cell called a zygote.
- The zygote divides rapidly as it travels down the fallopian tube.
- By the end of the week it becomes a blastocyst of about 100 cells.
- The blastocyst begins to implant into the uterine lining.
Changes for you
- Implantation may cause very light spotting (implantation bleeding) — normal.
- hCG hormone begins to be produced by the implanting embryo.
- Most women have no symptoms yet — it's too early.
Tips
- Continue folic acid daily.
- Avoid raw or undercooked foods (sushi, deli meats, soft cheeses) due to Listeria risk — Australian dietary guidelines apply.
- Stay alcohol-free from this point; no safe level of alcohol in pregnancy is known.
Warning signs
- Heavy bleeding (not just light spotting)
- Severe one-sided pain
Australian notes
- Food safety is important from conception. Food Standards Australia New Zealand (FSANZ) publishes safe food guidelines for pregnancy — see foodstandards.gov.au.