Week 5
Your baby is the size of a sesame seed
What's happening this week
Your baby has officially entered the embryonic stage — and the speed of development this week is staggering. At about the size of a sesame seed (roughly 2mm), your embryo is tiny but incredibly busy.
The neural tube — the structure that will become your baby's brain and spinal cord — is forming and beginning to close. This is exactly why folic acid matters so much right now. Adequate folate helps the neural tube close properly, reducing the risk of neural tube defects like spina bifida. If you've been taking your prenatal vitamin, you're already giving your baby a crucial advantage.
Here's the milestone that gives most parents chills: cardiac tissue is beginning to organize. The cells that will become your baby's heart are arranging themselves into a tube-like structure, and by the end of this week or early next week, they'll begin generating tiny electrical impulses — the very first flickers of cardiac activity. It's not a fully formed four-chambered heart yet (that develops closer to weeks 9-10), but it's the beginning.
The embryo has three distinct cell layers actively differentiating now. The ectoderm is forming the nervous system and skin. The mesoderm is building the circulatory system, bones, and muscles. The endoderm is shaping the digestive tract and lungs. Three layers, all working simultaneously, all building toward the same incredible goal.
Your body this week
If you just found out you're pregnant this week — welcome. Week 5 is one of the most common weeks for that positive test, since it's roughly one week past your missed period. You might be processing a swirl of emotions right now, and that's completely okay.
Physically, rising hCG and progesterone are starting to make themselves felt. Fatigue might hit harder than you expected — the kind where you could fall asleep at your desk by 2pm. Breast tenderness may intensify. You might notice you're urinating more frequently, which happens because your blood volume is already increasing and your kidneys are working harder.
For some people, early morning sickness begins creeping in this week. It might start as a vague queasiness or a sudden aversion to a smell that never bothered you before. Not everyone experiences nausea this early — some won't feel it until week 6 or 7, and about 20-30% of pregnant people experience very little nausea at all.
This is a good week to call your healthcare provider and schedule your first prenatal appointment if you haven't already. Most providers see patients between weeks 8 and 12, but calling now gets you on the calendar. If you're taking any medications, mention them during the call — your provider can advise which are safe to continue.
Contact your provider sooner if you experience heavy bleeding, severe abdominal pain, or dizziness — these could indicate a complication that needs evaluation.
For dads
If your partner told you she's pregnant last week — or even today — you might still be absorbing the news. That's normal. The reality of week 5 is that there's no bump, no ultrasound scheduled yet, and the whole thing can feel abstract. But behind the scenes, this is one of the most developmentally intense weeks of the entire pregnancy. Your baby's heart is starting to form. Understanding what's happening — even when you can't see it — helps you feel connected to a process that can otherwise feel like it's happening to someone else.
Your partner may be starting to feel the first physical symptoms: crushing fatigue, sore breasts, maybe some nausea. These aren't minor inconveniences — her body is undergoing a massive hormonal shift. One concrete thing you can do this week: take over dinner planning and cooking for the next few nights. Don't wait to be asked. If she's too tired to eat a full meal, keep snacks stocked — crackers, fruit, whatever she can stomach. Small acts of initiative mean more than grand gestures right now.
Common concerns
Is it normal to have no symptoms at 5 weeks?+
Yes — many people feel completely normal at 5 weeks. Pregnancy symptoms are driven by rising hormone levels, and the speed at which those levels rise varies from person to person. Some people don't experience noticeable symptoms until week 6, 7, or even later. A lack of symptoms does not mean anything is wrong with your pregnancy.
When should I schedule my first prenatal appointment?+
Call your healthcare provider as soon as you have a positive test. Most providers schedule the first visit between weeks 8 and 12, but calling early ensures you get on the calendar — popular practices book up fast. During the call, mention any medications you're taking and ask about any lifestyle changes they recommend.
Can I still exercise now that I'm pregnant?+
For most pregnancies, moderate exercise is not only safe but recommended. Walking, swimming, and prenatal yoga are excellent choices. The outdated idea that pregnant people should avoid all physical activity has been thoroughly debunked by ACOG. That said, avoid contact sports and activities with a high fall risk, and always check with your provider if you have specific concerns about your exercise routine.
When should I be concerned about cramping?+
Mild cramping is common in early pregnancy as your uterus begins to grow. It often feels similar to period cramps — a dull ache in your lower abdomen. However, contact your healthcare provider if cramping is severe, one-sided, accompanied by heavy bleeding, or comes with dizziness or shoulder pain. These could be signs of an ectopic pregnancy, which requires immediate evaluation.
Product picks for week 5
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Anti-nausea wristbands
Acupressure bands that apply gentle pressure to the P6 point on your wrist — many parents find they take the edge off early nausea.
Pregnancy planning binder
Organize your appointments, questions for your provider, insurance info, and birth preferences in one place from the start.
Insulated water bottle
Staying hydrated helps with fatigue and nausea — a good bottle makes it easier to sip throughout the day.
A quick note: This content is for informational purposes only and is not a substitute for professional medical advice. Always talk to your healthcare provider about any questions or concerns. Learn how we create our content.
Content based on guidance from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), Mayo Clinic, and peer-reviewed medical literature. Learn more about how we create our content.