18 weeks pregnant
Second trimester about 4 months
At 18 weeks pregnant, your baby is about the size of a mango.
Baby this week
About 140mm. The fetus is yawning, hiccupping, and rolling. Myelin — the protective sheath around nerves — is beginning to form and will continue developing after birth.
Did you know? Fetuses hiccup in the womb from around week 18 — you may feel rhythmic, repetitive jolts, which is completely normal and actually a sign of good diaphragm development.
What she may be feeling
- Strong, regular fetal movement
- Growing belly
- Back pain
- Heartburn
- Leg cramps
- Swelling in feet and ankles
- Varicose veins
- Stretch marks
Tips for her this week
- You may feel strong kicks, rolls, and jabs now — track movement patterns so you know your baby's normal.
- The anatomy scan at week 20 will check all major organs and structures.
- Heartburn can intensify as the uterus pushes against the stomach — stay upright after meals.
- Maternity clothes are likely a necessity by now if not already.
For partners
- You may be able to feel kicks from the outside now by placing your hand on her belly.
- Feeling the baby kick is a profound moment — be present and patient for it.
- The anatomy scan is just two weeks away — make absolutely sure you can attend.
- Start researching infant CPR and first aid courses — good to do before the baby arrives.
Partner to-do list
- Feel for kicks by placing your hand on her belly
- Confirm anatomy scan attendance — this is a must-attend appointment
- Research infant CPR classes in your area
- Continue nursery setup
This week together
- Prepare questions for the anatomy scan
- Decide if you want to confirm sex at the scan
- Finalize and refine the birth plan
- Begin finalizing baby names if you haven't
When to call your doctor or midwife
Contact your care provider right away, or call emergency services, if she has:
- Decrease in fetal movement (though tracking is more relevant from week 28+)
- Heavy bleeding
- Severe abdominal pain
- Fever
- Signs of UTI
Trusted guidance: NHS: Pregnancy · NHS: Pregnancy complications · ACOG: Pregnancy · Pregnancy Info: Your pregnancy
Common questions
How big is the baby at 18 weeks?
At 18 weeks pregnant, your baby is about the size of a mango. About 140mm.
How many months is 18 weeks pregnant?
18 weeks pregnant is about 4 months, in the second trimester.
What can partners do at 18 weeks?
You may be able to feel kicks from the outside now by placing your hand on her belly. Feeling the baby kick is a profound moment — be present and patient for it.