TL;DR
- Your baby is the size of a sesame seed, about 3mm
- The tiny heart has started beating — one of the earliest organs to function
- Morning sickness and fatigue may be ramping up
- Rest when you feel tired — your body is working hard behind the scenes
Your Baby This Week
At five weeks, your baby is about the size of a sesame seed — roughly 3mm from top to bottom. And this week brings one of the most awe-inspiring developments of the entire pregnancy: your baby's heart has started beating.
It doesn't look like a heart yet — it's more of a tiny tube that flickers with electrical activity — but it's beating. At first it pulses at around 80 beats per minute, but over the next few weeks it will speed up dramatically, eventually reaching 150 to 170 beats per minute. You won't be able to hear it yet (that comes around week 6-8 with a Doppler or ultrasound), but it's there, working away.
Your baby's circulatory system is one of the first to develop because every other organ system needs blood flow to grow. The heart is doing double duty right now, pumping blood through a rapidly expanding network of tiny blood vessels.
Beyond the heart, other major developments are underway. The neural tube is continuing to close and differentiate — the top end is becoming the brain and the bottom end is becoming the spinal cord. Tiny buds that will become arms and legs are starting to appear. The beginnings of the digestive and respiratory systems are taking shape. Your baby is still measured in millimeters, but the complexity of what's happening is staggering.
Your Body This Week
Welcome to the week when many people start feeling genuinely pregnant. If morning sickness hasn't made an appearance yet, it might arrive now. Despite the name, it can hit at any time of day — morning, noon, or 3 a.m. Some people feel mildly queasy, while others are hugging the bathroom floor. Both extremes and everything in between are normal.
Fatigue is likely getting more intense. The kind of tired you're feeling isn't the same as a bad night's sleep — it's a whole-body exhaustion driven by progesterone and the massive amount of energy your body is devoting to building a placenta and growing an embryo. Your blood volume is already starting to increase, and your heart is pumping harder to keep up.
You might notice mood swings, too. One minute you're fine, and the next you're crying at a commercial about puppies. Hormonal shifts are responsible, and they're completely normal. Be kind to yourself — growing a human being is emotional work as well as physical work.
Some people also start experiencing food aversions this week. Foods you used to love might suddenly smell revolting. Conversely, you might develop cravings for things you've never been interested in before. Your body is going through an enormous hormonal shift, and your senses are adjusting.
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Common Questions at Week 5
Is it normal to not feel pregnant at 5 weeks?
Yes, absolutely. Some people have strong symptoms by week 5, and others feel perfectly normal until weeks 7 or 8. Every pregnancy is different. The presence or absence of symptoms at this stage says nothing about the health of your pregnancy.
When will I be able to hear the heartbeat?
Most healthcare providers can detect a heartbeat via transvaginal ultrasound around weeks 6 to 7. If you have an early ultrasound at week 5, the heartbeat might not be visible yet — and that's completely normal. If your provider can't find it, they'll typically have you come back in a week or two for another look.
I'm having cramping. Should I be worried?
Mild cramping is very common in early pregnancy and is usually caused by your uterus expanding. It can feel similar to menstrual cramps. However, if the cramping is severe, one-sided, or accompanied by heavy bleeding, contact your healthcare provider right away, as these can be signs of an ectopic pregnancy or other complications.
Can morning sickness start this early?
It can. While many people associate morning sickness with weeks 6-9, it's not unusual for nausea to begin at week 5. HCG levels are doubling roughly every 48 hours at this point, and it's this rapid rise that's thought to trigger nausea. The good news is that for most people, morning sickness improves significantly by week 12-14.
This Week's Tip
Rest when you feel tired — your body is working hard behind the scenes. This might seem like simple advice, but it's surprisingly difficult to follow. Many people push through first-trimester exhaustion, trying to maintain their pre-pregnancy pace. But your body is building an entirely new organ (the placenta) and growing a tiny human being. That takes real energy. If you can, go to bed earlier. Take short naps when possible. Ask for help with tasks that drain you. This isn't laziness — it's your body telling you what it needs. The fatigue usually eases up in the second trimester, so this intense tiredness is temporary.
Sources
- American College of Obstetricians and Gynecologists (ACOG). How Your Fetus Grows During Pregnancy.
- Mayo Clinic. Fetal Development: The 1st Trimester.
