nuhahyearlyLaunch pricing - Get £50 off!nuhahyearlyAt week 4, your baby is the size of a poppy seed and has just implanted in the uterine wall. According to Nuhah's pregnancy guide, this is when hCG production begins - the hormone that pregnancy tests detect.
The blastocyst has implanted into the uterine wall. The amniotic sac and placenta are beginning to form. The embryo is now made of two layers of cells (epiblast and hypoblast) that will develop into all the organs and body parts. The cells that will become the placenta are burrowing into the uterine lining, establishing a blood supply.
You may experience light spotting (implantation bleeding) which is completely normal. hCG (human chorionic gonadotropin) production has begun, which is the hormone detected by pregnancy tests. Some people notice breast tenderness, mild cramping, or fatigue. A home pregnancy test may show a positive result by the end of this week, though it is more reliable from the day your period is due.
Most home pregnancy tests are accurate from the first day of your missed period. Some early detection tests work a few days before, but accuracy improves the longer you wait. Nuhah's due date calculator can help you work out dates once you have a positive result.
Light spotting that occurs when the fertilised egg attaches to the uterine wall, usually around 6-12 days after conception. It is typically lighter than a period, pinkish or brown in colour, and lasts 1-2 days. Not everyone experiences it.
About the size of a poppy seed, roughly 1mm. Your baby is a tiny cluster of cells that has just implanted in your uterine wall. Despite being microscopic, the foundations of every organ system are being laid.
Milestones, partner sharing, notes, photos, and a curated essentials guide - all free. No app to install.
Get Started - Free© 2026 Nuhah. All rights reserved.