Week 4 of Pregnancy
Your baby is about the size of a poppy seed (1-2 mm)
Your Baby This Week
Development milestones for week 4
At 4 weeks pregnant, your baby is officially an embryo, about the size of a poppy seed - just 1-2 millimeters. This tiny speck is already incredibly complex. The embryo has implanted into your uterine wall, and cells are rapidly differentiating into three distinct layers: the ectoderm (which will become skin, hair, and the nervous system), the mesoderm (which will form muscles, bones, and the circulatory system), and the endoderm (which will develop into internal organs). The neural tube, which will become your baby's brain and spinal cord, is beginning to form. The amniotic sac is developing to protect your baby, and the yolk sac is providing nutrients until the placenta fully takes over. Your baby's heart cells are forming, and within the next week or two, that tiny heart will begin to beat. Four weeks pregnant marks a milestone: you are officially pregnant.
Your Body This Week
Changes you may experience
This is the week you might get your BFP - Big Fat Positive - the moment every trying-to-conceive woman dreams about. Your period is due around now, and if it does not arrive, that is often the first sign that sends women running to the pharmacy for a pregnancy test. The pregnancy hormone hCG is rising rapidly, doubling approximately every 48-72 hours. Some women notice implantation bleeding around this time - light pink or brown spotting that can be mistaken for an early, light period. Many women share stories like "I thought my period was coming because I had cramps, then I took a test and there were two lines." Early pregnancy symptoms may begin appearing: heightened sense of smell, breast tenderness that feels different from PMS, fatigue, and for some lucky ones, the first waves of nausea. But many women feel nothing at all at 4 weeks - both are completely normal.
Tips & Advice for Week 4
Practical guidance from real moms
If you get a positive test, take a breath - you did it. Take a second test a few days later to confirm hCG is rising (the line should get darker). Call your OB or midwife to schedule your first prenatal appointment, typically scheduled around 8 weeks. Many practices will do blood work to confirm pregnancy before your appointment. Start a pregnancy journal or app to track symptoms and milestones. Be prepared for the emotional rollercoaster: joy, fear, disbelief, and anxiety often hit simultaneously. If your test is negative but your period does not arrive, wait a few days and test again - implantation might have occurred late. If you see light spotting, do not panic; implantation bleeding is common. Avoid announcing to the world yet - most couples wait until after the first trimester due to miscarriage risk. Confide in your partner and enjoy this secret for now.
Medical Guidance for Week 4
What to discuss with your healthcare provider
Once you have a positive test, call your healthcare provider to schedule your first prenatal appointment. They will likely order a beta hCG blood test to confirm pregnancy and ensure levels are rising appropriately. Watch for warning signs: heavy bleeding (soaking a pad), severe one-sided abdominal pain (could indicate ectopic pregnancy), or dizziness and fainting. Otherwise, continue prenatal vitamins and avoid alcohol, raw fish, and unpasteurized foods.
Disclaimer: For educational purposes only. Consult your healthcare provider for personalized medical advice.