Week 18 of pregnancy
Updated 8 Nov 2026
Your baby this week
About the size of a bell pepper
Source: Vinmec – Bảng cân nặng và chiều dài thai nhi theo tiêu chuẩn của WHO
Your baby's development
Your baby is about 14 cm long and weighs about 140 - 180 grams.
Myelin, a substance that protects the nerves, is starting to form and cover your baby's nerves; it will keep developing until it is complete by the day your baby is born. Your baby's hearing is also much more developed. Talk to your baby often, parents.
Ultrasound at this stage helps screen for structural abnormalities in your baby.
You may feel your baby hiccup or yawn, how exciting!
Your body
From this week on, your bump will grow visibly. Your legs and arms may swell slightly. Some mums-to-be feel dizzy, tired or even faint when changing position suddenly. So take care when moving around.
Back pain continues to bother you. Heartburn may ease; eat slowly and chew more thoroughly. A dark line will appear down the middle of your tummy. Melasma and freckles may also appear. This is caused by skin pigmentation changes due to hormones. These patches of pigment will disappear a few months after birth, so don't worry.
Advice for you
Get enough iron and calcium from food, or from the iron-calcium tablets your doctor prescribes. Rest and relax. Warm up and stretch your calf muscles to reduce cramps. Some fun but not too strenuous activities will also lift your spirits a lot, and starting a diary for your baby right in Momby from now is really worth doing.
Signs that need a doctor now
If you notice any of the signs below, please go to the nearest health facility to be checked by a doctor.
Vaginal bleeding in pregnancy
This sign needs to be checked by a doctor. Please go to the nearest health facility now. If the bleeding is heavy or comes with severe pain or faintness, call the emergency number 115.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Convulsions (fits)
A convulsion in pregnancy is an emergency. Family members should call 115 at once, lay the mother on her side in a safe place and get her to the nearest hospital.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Fever in pregnancy
A temperature above 38°C counts as a fever. Please go to a health facility so a doctor can find the cause and advise on safe ways to bring it down; do not take medicine on your own.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Leaking fluid or waters breaking
Fluid leaking from the vagina may mean the waters are leaking or have broken and needs to be checked by a doctor. Please go to a health facility soon, lying with your head low while travelling.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Severe headache, blurred vision, sudden swelling
Headache with blurred vision, or sudden swelling of the face, hands or eyelids, can be a sign of high blood pressure in pregnancy or pre-eclampsia. This sign needs to be checked by a doctor. Please go to the nearest health facility now.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Reduced or no fetal movement
A clear drop in the baby's movements, or no movement, needs to be checked by a doctor. Please go to the nearest health facility now rather than waiting until tomorrow.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Severe or worsening abdominal pain
Abdominal pain that keeps getting worse, does not ease, or is severe needs to be checked by a doctor. Please go to the nearest health facility now. If the pain is severe with sweating, faintness or bleeding, call 115.
Source: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
Sources
Content advised by our doctors.
- Bệnh viện Từ Dũ – Lịch khám thai định kỳ (accessed 22 Oct 2026)
- NHS – 18 weeks pregnant guide (accessed 22 Oct 2026)
- Vinmec – Sự phát triển của thai nhi tuần 18 (accessed 22 Oct 2026)
- Source for fetal size: Vinmec – Bảng cân nặng và chiều dài thai nhi theo tiêu chuẩn của WHO
- Source for the signs that need a doctor: Bệnh viện Đa khoa Tâm Anh – Các dấu hiệu nguy hiểm trong thai kỳ
This article helps you understand and prepare. It does not replace a check-up. For an answer about your own situation, please ask the doctor who is caring for you.