Week 5
Trimester 1Days 4+0 to 4+6
Baby is now the size of a sesame seed
For many people, Week 5 is the week when pregnancy starts to feel real. A missed period often leads to a pregnancy test, and many parents see their first positive result around this time. Although your baby is still incredibly tiny, some of the most important development of the entire pregnancy is already beginning — the foundations for the brain, spinal cord, heart, and major organs are now being formed. Pregnancy hormones are rising rapidly, which can bring a variety of new symptoms.
Length
~1–2 mm
0.4 in–0.8 in
Weight
< 1 g
2.2 lb
Development highlights
- check_circleThe embryo now has three distinct cell layers — ectoderm, mesoderm, and endoderm — that will form every organ and body part.
- check_circleThe neural tube is beginning to develop. This will eventually become the brain and spinal cord.
- check_circleThe structures that will become the heart are starting to appear.
- check_circleThe foundations for the lungs, liver, pancreas, and digestive system are forming.
This week's milestones
- check_circleThe embryo has three distinct germ layers — the building blocks of every organ in the body.
- check_circleNeural tube development begins — this is why folic acid is so important right now.
- check_circleThe early heart structure starts to form.
- check_circleThe placenta is developing rapidly to support the embryo.
Fun fact
Although your baby is only the size of a sesame seed, every major body system is already beginning to form this week.
Weekly checklist
- Continue taking prenatal vitamins.
- Schedule your first prenatal appointment if you haven't already.
- Stay hydrated.
- Get plenty of sleep.
- Eat regular meals to manage nausea.
- Start thinking about questions you want to ask your healthcare provider.
Frequently asked questions
Is it normal to feel exhausted?
Yes. Fatigue is one of the most common symptoms of early pregnancy. Your body is doing enormous work building the placenta and supporting a rapidly growing embryo.
Is cramping normal at Week 5?
Mild cramping can be normal as the uterus begins changing. Severe or one-sided pain should always be discussed with a healthcare professional promptly.
Should I be worried if I don't have symptoms?
No. Some people have many symptoms while others have almost none. The absence of symptoms does not mean anything is wrong.
Can I exercise during Week 5?
In most cases, yes. Continuing normal exercise is often encouraged unless your healthcare provider advises otherwise. Choose lower-intensity activities if you are feeling tired or unwell.
Related tools
shopping_bagHelpful picks for Trimester 1
Browse all pregnancy products →Frida Mom Anti-Nausea Acupressure Bands
Drug-free acupressure wristbands for morning sickness relief — wear during the first trimester to ease nausea without medication.
Lokaheadr 1st Pregnancy Essentials Kit
Curated first-pregnancy essentials gift set for new moms-to-be — everything you need for a comfortable first trimester.
Momcozy Maternity Pregnancy Pillow
Full-length maternity pillow with removable sections for bump support, back relief, and comfortable side sleeping.
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Medical information disclaimer
The content on this page is provided for general informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.
Always consult your GP, midwife, health visitor, paediatrician, or other qualified healthcare provider before making decisions about your health or your child's health and development. Never ignore or delay seeking professional advice because of something you have read on BabyScout. If you think there is a medical emergency, call 999 (UK) or your local emergency services immediately.