First trimester
5 weeks pregnant
The embryo is roughly the size of a sesame seed, and its heart begins to beat this week — often before you have seen anyone about the pregnancy. For many people this is also the week symptoms arrive in earnest.
Size of
sesame seed
Length
2 mm
Weight
< 0.001 g
Your baby at 5 weeks
The neural tube, which becomes the brain and spinal cord, closes during this week. This is the developmental step that folic acid supports, and it is why guidance emphasises taking it before conception rather than after a positive test.
A primitive heart tube forms and begins beating, typically around day 22 after conception. It is not yet a four-chambered heart, but it is pumping.
Small buds appear that will become arms and legs, and the beginnings of the eyes and ears are visible under magnification.
How you may be feeling
Nausea often begins around now. Despite the name, morning sickness frequently lasts all day, and for some people evening is worst. It is thought to be related to rising hCG, which is also why it often eases as hCG plateaus later in the first trimester.
Fatigue in the first trimester is frequently described as unlike ordinary tiredness — a heaviness that sleep does not fully resolve. Your body is building an entire organ, the placenta, which is genuinely demanding.
Common symptoms around week 5
- Nausea, with or without vomiting, often not limited to mornings
- Profound fatigue that rest does not fully fix
- Sore, heavy, or tingling breasts
- Needing to urinate more often, which starts earlier than most expect
- Food aversions, which can be sudden and absolute
Appointments and tests around now
If nausea is severe enough that you cannot keep fluids down, contact your provider rather than waiting it out. Hyperemesis gravidarum is a recognised condition with real treatments, and dehydration is the part that needs attention.
What is normal, and what varies
The absence of symptoms is not a bad sign. Plenty of people sail through the first trimester feeling almost normal and go on to have entirely uneventful pregnancies.
Worth doing this week
Eat before the nausea arrives
An empty stomach generally makes nausea worse. Small, frequent, bland food often works better than waiting until you feel able to eat a meal.
Prioritise fluids over food
If eating is difficult, staying hydrated matters more in the short term. Sips throughout the day beat large drinks.
Rest without guilt
First-trimester fatigue is physiological, not a failure of willpower. It typically eases in the second trimester.
Looking ahead
Next week the heartbeat may be visible on an early scan, and facial features begin to take shape.
Nearby weeks
Not sure which week you are in? The week tracker works it out from the first day of your last period, and the due date calculator gives you an estimated due date.