At 18 weeks pregnant you are a little over 4 months along, in the second trimester, with about 22 weeks to go until your estimated due date.
At 18 weeks pregnant your bump is starting to show, you may notice the first faint flutters of movement, and the anatomy ultrasound is coming up. New aches often join in too: a sore back, dizzy spells when you stand and calf cramps at night.
Every clinical detail below was read in October 2026 on the primary sources named in the text, and where they disagree we print both.
Key Takeaways
18 weeks is the second trimester, a little over 4 months, or 16 weeks after conception (Mayo Clinic), with about 22 weeks to go.
Mayo Clinic lists about 5 1/2 inches from crown to rump and about 7 ounces at week 18.
Cleveland Clinic says quickening usually happens around 16 to 20 weeks, and in a first pregnancy it is common not to feel movement until 20 weeks.
The anatomy ultrasound happens around 18 to 22 weeks (Cleveland Clinic). Learning the sex is your choice.
Seek care right away for bleeding, leaking fluid, severe belly pain, a severe headache, vision changes or fainting.
Table of Contents
18 Weeks Pregnant at a Glance
Quick Answer
At 18 weeks pregnant you are in the second trimester, a little over 4 months along (in your 5th month), with about 22 weeks to go. Mayo Clinic lists the baby at about 5 1/2 inches from crown to rump and about 7 ounces. First flutters and the anatomy ultrasound are both on the horizon.
18 weeks pregnant
What to know
Trimester
Second. UPMC, using the ACOG definition, says it runs from 14 weeks 0 days through 27 weeks 6 days.
Month
A little over 4 months, so you are in your 5th month. This counts 4 weeks and a few days per month. Months are a convention, not a medical unit.
Weeks to go
About 22 (40 minus 18, counted from the first day of your last menstrual period).
Baby’s size
About 5 1/2 inches (140 mm) crown to rump and about 7 ounces (200 g), per Mayo Clinic.
Common symptoms
Back and hip aches, dizziness, leg cramps, heartburn, a stuffy nose or nosebleeds.
This week’s care focus
The anatomy ultrasound and first flutters.
18 weeks pregnant: quick facts with sources.
How the weeks are counted. Cleveland Clinic explains that pregnancy is dated from the first day of your last menstrual period (LMP), about two weeks before conception, so Mayo Clinic calls week 18 16 weeks after conception. If an early ultrasound changed your due date, use the adjusted dates.
18 weeks pregnant in months. Eighteen weeks (126 days) is just over four calendar months. Cleveland Clinic’s guide puts weeks 17 through 20 in month 5.
Your Baby’s Development at 18 Weeks
These are the changes the major references tie to week 18 and nearby weeks.
Source and timing
What it says is happening
Mayo Clinic, week 18 (16 weeks after conception)
The ears begin to rise into their position on the head. The baby may start to hear sounds. The digestive system has begun working.
Cleveland Clinic, week 18
The fetus is covered in lanugo, a peach-fuzz hair that helps keep it warm. It may have a sleep-wake cycle, and loud noises may wake it.
Mayo Clinic, week 17
Toenails begin to develop. The baby rolls and flips, though you may not feel it yet.
Cleveland Clinic, week 19
The fetus is getting stronger, has its own unique fingerprints and can hiccup.
Fetal development around week 18, by source.
Can your baby hear you at 18 weeks? Cleveland Clinic says the ears can hear you talk by week 16; Mayo Clinic says the baby may start to hear sounds at week 18.
How Big Is Your Baby at 18 Weeks?
Only Mayo Clinic gives a week 18 figure. Nearby weeks are shown as each source wrote them.
Source
Week
Length
Weight
Mayo Clinic
16
About 4 3/4 inches (120 mm), crown to rump
About 4 ounces (110 g)
Cleveland Clinic
16 (end of month 4)
About 5 inches
About 4 ounces
Mayo Clinic
18
About 5 1/2 inches (140 mm), crown to rump
About 7 ounces (200 g)
Mayo Clinic
20
About 6 1/3 inches (160 mm), crown to rump
About 11 ounces (320 g)
Cleveland Clinic
20 (end of month 5)
About 9 to 10 inches
About 1 pound
Baby size near 18 weeks. Sources differ, so both are printed.
Why the numbers do not match. Mayo Clinic measures crown to rump, from the top of the head to the bottom, so the legs are not counted. Cleveland Clinic does not say how it measures. Cleveland Clinic compares the week 16 size to an avocado; we found no primary source comparison for week 18.
These are averages, and healthy babies vary. Ask your provider how your own baby is tracking.
18 Weeks Pregnant Symptoms
New aches often arrive as your body makes room for your baby. UPMC says to tell your doctor if morning sickness is still going on in the second trimester.
Symptom
What the sources say
What may help
Dizziness
Mayo Clinic links it to changes in blood flow during pregnancy.
Fluids, less standing, slow position changes; lie on your side if dizzy (Mayo Clinic).
Back and hip pain
Hormone changes and the growing uterus (Mayo Clinic); loosening ligaments and weight changes (UPMC).
Supportive low-heeled shoes; rest one foot on a stool when standing (Mayo Clinic).
Leg cramps
Mayo Clinic lists them among second trimester changes.
Stretch calves before bed, stay active, drink fluids (Mayo Clinic).
Heartburn
UPMC says the growing uterus presses on the stomach and pushes acid up the esophagus.
See the sleep section below.
Stuffy nose, nosebleeds, bleeding gums
Extra blood volume can make nasal tissue swell and bleed, and gums may bleed (Mayo Clinic).
Saline, a humidifier, a softer toothbrush (Mayo Clinic).
Common symptoms at 18 weeks pregnant, with what the sources suggest.
Swelling. Our sources describe swelling mainly as a warning sign. The Centers for Disease Control and Prevention (CDC) lists extreme swelling of the hands or face as an urgent warning sign, and UPMC says a severe headache with blurred vision, nausea or swelling of the face and hands could point to preeclampsia. UPMC also says one leg that is swollen, red and warm could be a blood clot.
Other changes. Mayo Clinic also lists melasma (darker patches on the face), a dark line down the belly, stretch marks, mild Braxton Hicks tightenings and a sticky clear or white discharge. Unsure about a tightening? See what contractions feel like.
Baby on the way? Get ahead on sleep.
Our free two-minute quiz builds a gentle, personalized sleep plan you can use from the first weeks at home.
Your 18 weeks pregnant belly. UPMC says body changes become much more noticeable in the second trimester as you start to show. Bumps vary a lot at the same week. Our pregnant belly by month guide shows the usual progression.
Appetite. UPMC says you need about 340 more calories a day in the second trimester.
Feeling your baby move. Cleveland Clinic says quickening usually happens around 16 to 20 weeks, though some people feel it sooner or later. It says early flutters feel like bubbles popping or tiny spasms and are easy to mistake for gas.
First pregnancy: Cleveland Clinic says it is common not to feel movement until 20 weeks.
Been pregnant before: Cleveland Clinic says you may notice it earlier, because your uterine muscles may be more relaxed and sensitive to movement.
Placenta position: Cleveland Clinic says an anterior placenta, one that sits at the front of the uterus, may make the first movements harder to feel.
UPMC says most people feel movement around 20 weeks, some as early as 16. No source we read asks you to count kicks this early. The CDC lists movement that stops or slows as an urgent warning sign.
Prenatal Care, Tests and Appointments Around Week 18
UPMC says second trimester visits are usually every four weeks. Mayo Clinic says your team checks your weight and blood pressure and measures fundal height (pubic bone to the top of the uterus).
What
Window
Details
Source
Anatomy ultrasound
Around 18 to 22 weeks
Looks at the baby’s organs and body, the placenta, the umbilical cord and the amniotic fluid. About 45 minutes.
Cleveland Clinic
Quad screen
Between 15 and 22 weeks
A blood screening test.
UPMC
Amniocentesis
Between 15 and 20 weeks
Optional, offered when other tests or your history suggest a higher risk.
UPMC
Glucose screening
Between 24 and 28 weeks (coming up)
A high result needs a second test.
UPMC
Flu and COVID-19 vaccines
Flu vaccine in fall or early winter
Mayo Clinic suggests a COVID-19 vaccine if you have not had one.
Mayo Clinic
Tests, scans and vaccines around 18 weeks, as read in October 2026.
The 18 weeks pregnant ultrasound. Week 18 is the start of the anatomy scan window. Cleveland Clinic says the sonographer checks the heart, brain, spine, kidneys, limbs, face and other organs, records the heart rate, and looks at the umbilical cord, the placenta, the amniotic fluid and your uterus, ovaries and cervix.
Cleveland Clinic notes the scan does not diagnose anything, does not find every congenital condition, and can give false results. Cleveland Clinic says the scan is not dangerous for you or the fetus.
Learning the sex is optional. Cleveland Clinic says the technician may be able to see the genitals, depending on the baby’s position. Want a surprise? Say so before the scan starts.
Vaccine guidance changes. The vaccine line above reflects the Mayo Clinic page as read in October 2026, so confirm flu, COVID-19 and any other vaccines with your own provider.
What to Do This Week: A Simple Checklist
Book the anatomy scan: or confirm the date if it is already set, and decide in advance whether you want to learn the sex.
Pay attention to flutters: note when you first notice them to share at your next visit.
Ease the aches: stand up slowly, stretch your calves before bed and wear supportive shoes (Mayo Clinic).
Keep moving: UPMC says you can keep exercising but may need to modify it to avoid back or hip pain, with walking and swimming as low-impact options.
Save the warning signs: read the list at the end of this guide and keep your provider’s after-hours number handy.
Thinking about a trip? If you are dreaming of a getaway, talk with your provider before you book, especially for flights or travel abroad, and read our babymoon guide for planning ideas.
Sleep at 18 Weeks Pregnant
Sleep can get harder as pregnancy goes on. MedlinePlus lists finding a comfortable position, bathroom trips, a faster heart rate, heartburn at night, worry and vivid dreams.
Sleep position. MedlinePlus says lying on your side with your knees bent will likely be the most comfortable position. It adds that many providers tell pregnant women to sleep on their left side, because it keeps the baby from pressing on the large vein that carries blood back to the heart from your legs, and that switching to the right side for a while is OK. In its words, it is best not to sleep flat on your back. Ask your provider what they want you to do.
Use pillows: under your belly or between your legs, or a rolled-up blanket at the small of your back (MedlinePlus). Our guide on how to use a pregnancy pillow walks through setups.
Night leg cramps: press your feet hard against the wall or stand on the leg (MedlinePlus).
Heartburn and bathroom trips: avoid a big meal or a lot of fluid within a few hours of bedtime (MedlinePlus).
Steady routine: same bedtime and wake time, and a 15-minute warm bath (MedlinePlus).
Sleep aids. MedlinePlus says not to take any sleep aids, including over-the-counter and herbal products. Our guide on whether you can take melatonin while pregnant covers the questions to ask.
For Partners: How to Help at 18 Weeks
Come to the anatomy scan: Cleveland Clinic says it takes around 45 minutes.
Be patient about kicks: Cleveland Clinic says early movements are subtle and easy to mistake for gas.
Take on standing and lifting jobs: to spare a sore back.
Learn the warning signs: so you can make the call if she is unsure.
Looking Ahead: What Comes Next
Week 19: Mayo Clinic says vernix caseosa forms, and Cleveland Clinic says most people begin to feel kicks and punches.
Week 20: the halfway point. Mayo Clinic says you might be able to feel movements by now.
Call any time something worries you. The CDC’s urgent maternal warning signs list says to seek medical care immediately for any of these during pregnancy:
A headache that will not go away or keeps getting worse.
Dizziness or fainting, or vision changes such as flashes of light, blind spots or blurriness.
A fever of 100.4 F (38 C) or higher.
Extreme swelling of the hands or face.
Trouble breathing, chest pain, or a fast-beating or irregular heart.
Severe belly pain that does not go away, or severe vomiting so you cannot keep fluids down.
Your baby’s movement stopping or slowing.
Vaginal bleeding or fluid leaking.
Severe swelling, redness or pain in a leg or arm.
Thoughts about harming yourself or your baby.
Also call for pain when you urinate (UPMC), contractions that become regular and keep getting stronger, which Mayo Clinic says could signal preterm labor, or discharge with a strong smell or unusual color (Mayo Clinic).
When you call, say how many weeks pregnant you are; the CDC says to tell any provider you are pregnant. If you cannot reach your provider quickly, go to labor and delivery or the nearest emergency room. If it feels like an emergency, such as heavy bleeding, severe trouble breathing or a seizure, call 911. This article is general education, not medical advice.
Frequently Asked Questions
How many months is 18 weeks pregnant?
A little over 4 months. Eighteen weeks is 126 days, just past four calendar months counted from the first day of your last period. Cleveland Clinic’s guide places weeks 17 through 20 in month 5, so week 18 is often called the fifth month. Your provider counts in weeks, which is more precise.
How big is my baby at 18 weeks?
Mayo Clinic lists about 5 1/2 inches (140 millimeters) from crown to rump, meaning head to bottom without the legs, and about 7 ounces (200 grams) at week 18. Cleveland Clinic gives about 9 to 10 inches and 1 pound at week 20, without saying how it measures.
Should I feel my baby move at 18 weeks?
You may or may not. Cleveland Clinic says quickening usually happens around 16 to 20 weeks, and in a first pregnancy it is common not to feel movement until 20 weeks. An anterior placenta can make early movements harder to notice. Ask your provider if you have questions.
What does the 18 week ultrasound check?
Cleveland Clinic says the anatomy ultrasound, done around 18 to 22 weeks, checks the baby’s heart, brain, spine, kidneys, limbs and face, plus the placenta, cord and amniotic fluid, in about 45 minutes. It does not diagnose anything and cannot find every condition.
Can you find out the sex at 18 weeks?
Often, if you want to. Cleveland Clinic says the technician may be able to see the genitals during the anatomy ultrasound, depending on the baby’s position. Learning the sex is optional. If you want a surprise, tell the sonographer before the scan begins so nobody spoils it by accident.
What position should I sleep in at 18 weeks pregnant?
MedlinePlus says lying on your side with your knees bent is likely the most comfortable position, that many providers suggest the left side, and that it is best not to sleep flat on your back. Pillows under your belly or between your legs can help. Ask your provider what they recommend.
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