18 weeks pregnant: scan time and a first flutter
Your detailed mid-pregnancy scan window opens this week. Here is what it checks, what it cannot, and what else changes.
Updated October 13, 2026 · sources checked October 13, 2026
In short
At 18 weeks your baby is about 14cm long from head to bottom, wriggling a lot, with hearing, swallowing and sucking reflexes developing. You may feel a first fluttering. The detailed scan window opens: 18 to 21 weeks in England, 18 to 22 weeks in the US. This week, check your scan date and decide whether you want to know the sex.
Where you are at 18 weeks
You are in month five by Cleveland Clinic's grouping (weeks 17 to 20), and close to halfway. To see exactly how many weeks and days you are today, use the pregnancy week calculator; the due date calculator shows the finish line.
Your baby this week
The NHS gives a length of around 14.2cm from head to bottom and compares it to a bell pepper. Hearing, feeling, swallowing and sucking reflexes are developing, and your baby is wriggling and moving arms and legs a lot (NHS).
Cleveland Clinic adds that your baby is now covered in lanugo, a fine downy hair, may have a sleep-wake cycle, and can be woken by loud noises. ACOG's description of weeks 17 to 20 includes the part of the brain controlling movement being fully formed and ears, nose and lips becoming recognisable on ultrasound.
Your body and common symptoms
A first flutter. It can feel like bubbling or fluttering in your belly. If you have not felt anything yet, that is normal: the NHS gives 16 to 24 weeks, often after 20 weeks in a first pregnancy.
Dizziness. Your blood pressure is probably a bit lower than before, so the NHS suggests getting up slowly from the sofa or bed.
Clumsiness and bigger breasts. Your breasts may have gone up a size, especially in a first pregnancy, and a bigger belly can make you feel clumsy (NHS).
Linea nigra. A dark line down the middle of your tummy is normal skin pigmentation and usually fades a few months after birth (NHS).
Also common now: stretch marks and round ligament pains on the sides of the bump.
Is this normal? When to call
Light-headedness when you stand up quickly, a dark line on your tummy and not feeling movements yet are all normal at 18 weeks.
Call your midwife, GP or OB-GYN straight away if you faint, have vaginal bleeding or fluid leaking, severe or lasting tummy pain, or a temperature of 38C (100.4F) or above. In the UK, contact your early pregnancy unit or maternity unit, or NHS 111; call 999 in an emergency. In the US, call your provider, or 911 in an emergency.
Appointments and tests around 18 weeks
The detailed scan.
| United States | England | |
|---|---|---|
| Name | Standard (anatomy) ultrasound exam | 20-week screening scan, also called the anomaly scan |
| Timing | Usually 18 to 22 weeks (ACOG) | Usually 18 to 21 weeks, sometimes up to 23 weeks (NHS) |
| What it looks at | Major physical differences in the brain and spine, face, abdomen, heart and limbs (ACOG) | Signs of 11 conditions, your baby's growth, the placenta and blood flow in the womb (NHS) |
The NHS is clear that the scan cannot find everything, and that it is your choice whether to have it. It will not hurt, though the sonographer may press a little on your tummy. Practical tips from the NHS: arrive early, wear loose clothes, take out a belly piercing, bring paper notes if you have them, and check whether you need a full bladder or have to pay for pictures.
Also around now: the US quad screen window (15 to 22 weeks, ACOG) if you chose it; in the UK, the whooping cough vaccine from 16 weeks, usually given around the 20-week scan.
Your checklist for week 18
For your partner
Clear your diary for the scan if you can, and talk beforehand about whether you both want to know the sex. Whatever you see on the screen, you are there to listen first.
Previous and next week
Week 17: first flutters and stretch marks · Week 19: relaxin, sleep and pelvic pain
Read the full second trimester guide or see all pregnancy weeks.
Questions parents ask
What should my bump look like at 18 weeks?
There is no single right size. The NHS explains that bump size depends on your hormones, your weight before pregnancy, how many babies you have had and the strength of your muscles. Your midwife or doctor checks growth at your appointments.
How many months is 18 weeks pregnant?
Cleveland Clinic groups weeks 17 to 20 as month five, so 18 weeks is in the fifth month.
Will I find out the sex at the 18 to 20 week scan?
Possibly. The NHS says the sonographer may be able to tell you, but not everyone wants to know and some hospitals do not reveal it. If you do not want to know, say so before the scan starts.
Sources
- NHS — Week-by-week guide to pregnancy, week 18 checked October 13, 2026
- NHS — 20-week screening scan checked October 13, 2026
- ACOG — Ultrasound Exams checked October 13, 2026
- ACOG — Prenatal Genetic Screening Tests checked October 13, 2026
- Cleveland Clinic — Fetal Development, week-by-week stages checked October 13, 2026
- NHS — Week-by-week guide to pregnancy, week 12 (what affects bump size) checked October 13, 2026
Mamavela explains; it does not replace your midwife, doctor or pediatrician, who know your situation. If something worries you, call them. In an emergency, call 911 (US), 999 (UK) or 112.