Our Baby Journey18 weeks pregnant
18 weeks pregnant is about 4 months. It falls in the fifth month of pregnancy. You are in week 18 of 40, in the second trimester. Here is what is happening with your baby and your body this week.
Your baby is about the size of a bell pepper.
Length: about 14.2 cm (5.6 in) from crown to rump · Weight: about 190 g (6.7 oz)
Your baby at 18 weeks
The baby can hear sounds, including your heartbeat and voice. The nervous system is maturing.
Your baby's ears are now in their final position, and the tiny bones of the middle ear and the nerve endings from the brain are developed enough to pick up sounds. Your heartbeat, your digestion, and the muffled sound of your voice are part of their surroundings.
A protective coating called myelin is beginning to form around the nerves. Myelin helps nerve signals travel quickly and efficiently, and this process will continue well into childhood.
The reproductive organs are well developed. In girls, the uterus and fallopian tubes have formed; in boys, the genitals are usually visible on ultrasound. Your baby is very active, yawning, hiccuping, stretching, and changing position often, and may now be large enough for you to notice movement, especially if you have been pregnant before. Your baby also has periods of rest and activity during the day.
Your body at 18 weeks
Back pain and dizziness can occur. Stand up slowly to avoid lightheadedness.
During the second trimester your blood pressure is often lower than usual, as your blood vessels relax to carry the extra blood. Combined with your growing uterus pressing on blood vessels when you lie on your back, this can make you feel dizzy or lightheaded, especially if you stand up quickly, get too hot, or go without eating for a while. Back pain is common as your posture changes. Some people also start to get leg cramps at night or notice mild swelling in their feet at the end of the day.
Your belly at week 18
In month 5 (weeks 18–22) your bump is usually clearly visible. At about 20 weeks the top of the uterus reaches your belly button. From around 20 weeks, your fundal height (the distance in centimeters from your pubic bone to the top of the uterus) roughly matches the number of weeks you are pregnant, give or take about 2 cm.
Belly size and shape vary a lot depending on your build, whether this is your first pregnancy, your baby's position and the amount of amniotic fluid. At checkups your doctor or midwife may measure your fundal height to track your baby's growth, and may arrange an ultrasound if the measurement is quite different from what they expect.
Symptoms at 18 weeks pregnant
- Dizziness or lightheadedness
- Lower back pain
- Leg cramps, often at night
- Mild swelling of the feet
- Possible feelings of movement
- Heartburn
Checkups around week 18
The detailed anatomy scan, also called the anomaly or mid-pregnancy scan, is usually done between about 18 and 22 weeks. It checks your baby's growth and organs, the position of the placenta, and the amount of amniotic fluid. The exact week varies by country and clinic.
Tips for week 18
- Talk, read, or sing to your baby.
- Avoid lying flat on your back for long periods.
- Your anatomy scan is usually scheduled around weeks 18–22.
Common symptoms in the second trimester
The second trimester runs from week 14 to week 27. Nausea often eases, energy returns, your bump starts to show, and you will begin to feel your baby move. Not everyone has every symptom, and it is normal for symptoms to come and go. Common ones include:
- A growing bump and weight gain
- First baby movements, usually felt between weeks 16 and 25
- Round ligament pain (sharp pains low in the belly or groin)
- Heartburn and indigestion
- Back ache
- A blocked nose or nosebleeds
- Leg cramps
- Skin changes such as a dark line on the belly or darker patches on the face
Read the full second trimester guide.
When to call your doctor or midwife
Contact your healthcare provider or maternity unit straight away, or get emergency care, if you have:
- Vaginal bleeding
- Severe or persistent abdominal pain or cramping
- A severe headache, blurred vision, or sudden swelling of your face, hands or feet
- A fever of 38°C (100.4°F) or higher
- Fluid leaking from your vagina
- Severe vomiting where you cannot keep fluids down
- Your baby moving less than usual or a change in their pattern of movements (later in pregnancy)
- Regular contractions before 37 weeks
- Pain or burning when you urinate
- Feeling very low, anxious, or having thoughts of harming yourself
Have a question about week 18?
Ask our AI pregnancy assistant about symptoms, nutrition, scans or anything else on your mind this week.
Frequently asked questions
How big is my baby at 18 weeks pregnant?
At 18 weeks pregnant, your baby is about the size of a bell pepper. That is about 14.2 cm (5.6 in) from crown to rump, weighing about 190 g (6.7 oz).
How big is my belly at week 18 of pregnancy?
In month 5 (weeks 18–22) your bump is usually clearly visible. At about 20 weeks the top of the uterus reaches your belly button. From around 20 weeks, your fundal height (the distance in centimeters from your pubic bone to the top of the uterus) roughly matches the number of weeks you are pregnant, give or take about 2 cm. Bump size, shape and when you start to show vary a lot from person to person.
What does the anatomy scan check?
The anatomy scan looks in detail at your baby's brain, face, spine, heart, stomach, kidneys, and limbs, and measures their growth. It also checks where the placenta is lying and the amount of amniotic fluid. The scan can find many physical differences but not every condition. Most scans are reassuring, and if anything needs a closer look, your provider will explain the next steps.
Will I find out the baby's sex at the anatomy scan?
Often, yes, if you want to know and if the baby is lying in a position that allows a clear view. The sonographer isn't always able to tell, and some hospitals have policies about whether they share the sex. If you would rather keep it a surprise, let the sonographer know at the start of the scan.
Why do I feel dizzy at 18 weeks?
Dizziness is common in the second trimester because blood pressure tends to drop and your circulation is adjusting to more blood. Standing up slowly, eating small regular meals, drinking enough water, avoiding overheating, and lying on your side can help. If you faint, or your dizziness comes with blurred vision, a severe headache, a racing heartbeat, or chest pain, contact your doctor or midwife promptly.
What trimester is 18 weeks pregnant?
Week 18 is in the second trimester, which covers weeks 14 to 27.
How many months is 18 weeks pregnant?
18 weeks pregnant is about 4 months. It falls in the fifth month of pregnancy. The fifth month covers weeks 18 to 22. Pregnancy is about 40 weeks, or roughly 9 months, counted from the first day of your last period.
This page is general educational information and is not a substitute for advice from your doctor or midwife. Every pregnancy is different, and baby sizes are approximate averages. Last updated 2026-11-07. See our medical disclaimer.