mybabybase

First trimester

5 weeks pregnant

Baby is about the size of a sesame seed.

Week 5 of 40 · in your first trimester · Updated

Your baby this week

The neural tube (brain & spine) is forming. The tiny heart is beginning to develop.

  • The neural tube — which becomes the brain and spinal cord — closes this week. (This is exactly why folic acid is so critical.)
  • Three layers of cells are now distinct: ectoderm (brain, skin, nails), mesoderm (heart, bones, muscles), endoderm (lungs, gut).
  • The heart starts as a simple tube that will fold and divide over the next week.

Your body this week

Morning sickness, sore breasts, and fatigue can kick in. Hormone levels rising fast.

  • hCG is still doubling rapidly. This is what's driving the first big wave of symptoms.
  • Your blood volume is starting to increase — eventually you'll have about 50% more blood than before pregnancy.
  • Tiredness can be intense and not what you've felt before. It's normal.

Common symptoms

  • Nausea
  • Bone-deep fatigue
  • Tender or tingling breasts
  • Heightened sense of smell
  • Food aversions
  • Bloating

Things to do this week

  • Start eating small frequent meals if nausea is hitting
  • Sleep 9+ hours when you can
  • Avoid raw/undercooked meat, fish, and unpasteurized dairy

For partners this week

Take on the smelly jobs

  • Take over cooking and taking out the garbage if smells are setting off nausea.
  • Keep plain crackers and water by the bed.
  • Pick up extra chores so naps can happen.

Typical visits around this week

Based on a typical schedule in Ontario. Your doctor or midwife sets the actual timing.

Coming up

  • First prenatal visit

    Weeks 6–12

    Book with your doctor or midwife as soon as you know you're pregnant. This is usually the longest visit: your health and family history, medications, blood pressure and weight, and routine blood and urine tests (including your blood type and Rh factor). Your provider will also talk about your due date and the screening options ahead.

    Questions to ask →
    • When is my estimated due date, and how was it worked out?
    • Are my current medications and supplements okay to keep taking?
    • Who will care for me during pregnancy and birth, and where would I give birth?
    • Who do I call with questions or worries between visits?
    • Which vaccines should I plan for this pregnancy?

  • Dating ultrasound

    Weeks 7–12

    An early ultrasound that measures the baby to confirm how far along you are. Dating is most accurate between about 7 and 12 weeks, and the scan also confirms the pregnancy is in the uterus.

    Questions to ask →
    • Does this scan change my due date?
    • Can my partner come into the room?
    • Do I need a full bladder, and how should I prepare?
    • When will my provider get the results?

When to call your doctor or midwife

Bleeding, fluid leaking, a bad headache or vision changes, or baby moving less than usual all need a call. See the warning signs and who to call →

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Follow your pregnancy week by week in MyBabyBase.

A due-date countdown, a mood and symptom journal, appointments, and a safe place for your documents — all in one hub.

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Further reading from health authorities