18 weeks pregnant: the anomaly scan and first movements
18 weeks pregnant is a stage at which, the NHS says, the baby is around 14.2 cm long, about the size of a bell pepper, and the NHS says you may feel your baby move for the first time (NHS, 2026). This page sets out what the NHS, NICE, ACOG and the Office on Women’s Health say about week 18, including when the anomaly scan is offered.
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Seek help now if you have any of these symptoms
Bleeding and cramping are common in early pregnancy and often do not mean miscarriage. The symptoms below, however, need to be assessed straight away.
- Soaking two or more sanitary pads per hour, or passing large clots
- Severe lower abdominal pain, especially on one side
- Pain at the tip of the shoulder
- Dizziness, fainting, or collapse
- Signs of shock — pale, clammy, rapid heartbeat, breathlessness
- Pain on opening bowels, or bladder or bowel changes
- Feeling very unwell, or feverish
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How the sources describe development around 18 weeks
- Size and shape, NHS
- The NHS week 18 page in its week-by-week guide (NHS, 2026) gives the baby as around 14.2 cm long and compares it to a bell pepper. It says the hearing, feeling, swallowing and sucking reflexes are developing this week, and that the baby will be doing a lot of wriggling around and moving the arms and legs.
- Development, ACOG
- ACOG’s list for weeks 17 to 20 includes the part of the brain that controls motor movements being fully formed, the digestive system working, ears, nose and lips recognisable on an ultrasound, and, in girls, the uterus and vagina starting to form (ACOG, How Your Fetus Grows During Pregnancy, 2024). It does not date these to a single week.
Weeks are counted from the first day of the last menstrual period, so about two weeks of the count come before conception (ACOG, How Your Fetus Grows During Pregnancy, 2024). This page covers 18 weeks 0 days to 18 weeks 6 days.
A normal pregnancy lasts about 40 weeks from the first day of the last menstrual period, so at 18 weeks about 22 weeks remain to the estimated due date (ACOG, How Your Fetus Grows During Pregnancy, 2024). Your own due date depends on your last period or a scan, not on the week alone.
The anomaly scan: the windows differ by document
- The NHS week 18 page says you will be offered an anomaly scan at around 18 to 20 weeks, which looks at your baby in detail to see if there is anything unusual about their development and appearance, and adds that it can pick up a range of conditions but not all of them (NHS, "Week 18 of pregnancy", 2026).
- The NHS page on antenatal appointments gives the window as 18 to 21 weeks (NHS, "Antenatal (pregnancy) care and appointments", 2026).
- NICE guideline NG201 recommends offering the scan between 18 weeks 0 days and 20 weeks 6 days, to screen for fetal anomalies and determine where the placenta is (NICE, 2021).
- In the US, the Office on Women’s Health says it is not uncommon to have a standard ultrasound between 18 and 20 weeks to look for signs of problems with the baby’s organs and body systems, and to confirm the age of the fetus and proper growth (Office on Women’s Health, Prenatal care and tests, undated).
The NHS says the sonographer may be able to tell you the baby’s sex at this scan, but that not everyone wants to know and it is not always hospital policy to reveal it, so tell them before the scan starts if you do not want to know (NHS, "Week 18 of pregnancy", 2026).
Your body at 18 weeks, as the NHS describes it
The NHS says that if you feel your baby move for the first time it may feel like a gentle fluttering, bubbling sensation. It says you may feel a bit clumsier, that your blood pressure is probably a bit lower than it was so you should not leap up from the sofa or you could feel dizzy, and that you may notice a line down your stomach called the linea nigra, which it describes as normal skin pigmentation (NHS, "Week 18 of pregnancy", 2026).
Work out which week you are in
The Pregnancy week calculator takes your last period, conception date, scan or IVF transfer and shows how many weeks and days pregnant you are today.
Sources
- NHS Best Start in Life. Week 18 of pregnancy (week-by-week guide to pregnancy). nhs.uk, 2026.
- NHS. Antenatal (pregnancy) care and appointments. nhs.uk, 2026.
- National Institute for Health and Care Excellence. Antenatal care (NG201). NICE, 2021.
- American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy (FAQ156). ACOG, 2024.
- Office on Women's Health, US Department of Health and Human Services. Prenatal care and tests. womenshealth.gov.
Frequently asked questions
When is the anomaly scan?
The NHS week 18 page says around 18 to 20 weeks, its appointments page says 18 to 21 weeks (NHS, 2026), and NICE guideline NG201 recommends 18 weeks 0 days to 20 weeks 6 days (NICE, 2021). Your maternity service gives you your date.
Can the anomaly scan show the baby’s sex?
The NHS says the sonographer may be able to tell you at this scan, but that not everyone wants to know and it is not always the hospital’s policy to reveal it (NHS, 2026).