Baby is the size of a sesame seed
👶 Baby's development
The neural tube — future brain and spinal cord — starts forming. A heart precursor appears.
💛 How mom feels
Breasts may become tender. Possible morning sickness. Mood swings from hormones.
📖 Tip of the week
The neural tube is actively closing — folic acid is especially critical right now. The baby's heart is making its first beats, though it can't yet be heard on ultrasound. Morning sickness at this stage is normal: small frequent snacks and ginger tea can help.
🔬 Detailed baby development
- The embryo's neural tube, which becomes the brain and spinal cord, begins to form
- The heart starts as a simple tube-like structure and begins its first contractions
- Arm and leg buds begin to appear as tiny protrusions from the embryo's body
- The embryo is about 1.25 mm long, roughly the size of a sesame seed
- Blood vessels form and the primitive circulatory system starts to develop
- The embryo curves into a C-shape as rapid growth continues
🤱 What mom may feel
- Morning sickness or nausea may begin, often triggered by certain smells or foods
- Increased urination frequency as the uterus begins pressing on the bladder and kidneys filter more blood
- Heightened sense of smell that can trigger nausea
- Mood swings caused by rapidly changing hormone levels
- Persistent fatigue and a strong need for extra sleep
🏥 Tests and check-ups
If you haven't already, schedule your first prenatal appointment. Your provider may order blood work including blood type, Rh factor, complete blood count (CBC), and immunity to rubella. A dating ultrasound may be performed if the exact date of conception is uncertain.
💡 Tips for this week
- Eat small, frequent meals to help manage nausea throughout the day
- Keep crackers or dry toast by your bed to eat before getting up in the morning
- Continue prenatal vitamins; if they worsen nausea, try taking them at night with food
- Get plenty of rest — your body is working hard even though the embryo is tiny
- Avoid strong odors that trigger nausea, and keep rooms well ventilated
❓ Frequently asked questions
When will I hear the baby's heartbeat?
A heartbeat is usually detectable by transvaginal ultrasound around week 6. At week 5, the heart is just beginning to form, so it is typically too early to detect a heartbeat.
Is morning sickness only in the morning?
Despite the name, nausea can occur at any time of day or night. It is caused by rising hCG and estrogen levels and commonly peaks between weeks 8 and 12.
Should I tell people I'm pregnant at 5 weeks?
This is a personal decision. Many couples wait until after the first trimester (around 12 weeks) when the risk of miscarriage drops significantly. However, some prefer early support from close family and friends.
Is caffeine safe during pregnancy?
Moderate caffeine intake (under 200 mg per day, about one 12-oz cup of coffee) is considered safe by ACOG. Excessive caffeine has been linked to increased miscarriage risk.
📝 Week 5 of pregnancy: detailed guide
At week 5, the embryo is roughly the size of a sesame seed — about 2 mm — yet remarkable changes are underway inside. The neural tube, which will become the brain and spinal cord, is forming along the embryo’s back. The primitive heart tube has begun to beat, pumping blood through the earliest vessels. The three germ layers are now differentiating rapidly: the ectoderm is forming the foundations of the nervous system, while the endoderm and mesoderm are laying down the organs. Your hCG levels are doubling approximately every 48 hours, which is why a pregnancy test will now give a clear positive result.
For many women, morning sickness makes its first proper appearance this week. Despite its name, nausea can strike at any time of day or night, and it is caused by the rapid rise in hCG and oestrogen. You may also notice an intensified sense of smell — even previously pleasant aromas (coffee, cooked meat, perfume) can become overwhelming. Breast tenderness typically increases, the areolae may begin to darken, and extreme fatigue is very common. Your body is working hard to build a placenta while simultaneously adapting every system to support a pregnancy.
If you have not yet contacted your GP or midwife, do so now. Confirm that you are taking folic acid 400 mcg each day; women with a BMI over 30, a family history of neural tube defects, or who are taking certain medications (such as anti-epileptics) should take the higher dose of 5 mg as recommended by NICE guidelines. Begin taking a daily vitamin D supplement of 10 mcg, as recommended throughout pregnancy in the UK. Avoid X-rays and inform any dental or medical practitioners that you are pregnant before any procedure or prescription.
To ease nausea, eat small, frequent meals every two to three hours rather than three large ones — an empty stomach often makes queasiness worse. Keep dry crackers or plain oat biscuits by the bed and eat a few before rising in the morning. Cold foods and foods with a mild smell tend to be better tolerated. Ginger — as a tea, biscuit, or lozenge — has good evidence behind it for reducing pregnancy nausea. Stay well hydrated with small, frequent sips of water or diluted fruit juice. If you cannot keep any fluids down, contact your midwife or GP promptly.
⚠️ When to see a doctor
- Heavy bleeding or spotting
- Severe abdominal pain or pain on one side
- Severe nausea and vomiting (unable to eat or drink)
- Fever above 38°C (100.4°F)
- Pain or burning during urination
- Dizziness or fainting
Sources
- WHO recommendations on antenatal care (2016)
- ACOG Practice Bulletins
- Williams Obstetrics, 26th Edition
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