Week 18
Your baby is the size of a sweet potato
Your baby's ears are now standing out from the head. The digestive system just started working. And sounds may begin to reach your baby for the first time through the layers of your body. At 18 weeks, your baby measures about 5 and a half inches from crown to rump and weighs 7 ounces. Sweet-potato-sized. The anatomy scan is likely this week or next, and the pregnancy is starting to feel less abstract.
Key takeaways
- Your baby's ears are now in their final position on the head and may begin to register sound, though consistent fetal responses to external noise don't show up reliably in studies until closer to 28 weeks.
- Round ligament pain (that sharp pull in your groin when you stand up too fast) is common in the second trimester as your uterus and ligaments stretch. Slow movements help.
- The anatomy scan is performed between 18 and 22 weeks per ACOG, with 18 to 20 weeks generally considered the best window for clear imaging. Complex organs like the heart and brain image clearly at this stage. Block the appointment.
- The digestive system just started working, and your baby is swallowing amniotic fluid and producing meconium that won't make an appearance until after birth.
Your baby's ears are popping out and starting to listen
Your baby is sweet-potato-sized this week, measuring about 5 and a half inches from crown to rump and weighing 7 ounces.
The headline: the ears are now standing out from the head, sitting in their final position on the sides of the skull, per Mayo Clinic's review of fetal development. Up to this point they were lower and closer to the neck.
Now they're recognizably ears.
Hearing is also starting to come online. Mayo Clinic notes your baby may begin to hear sounds this week, though consistent fetal responses to external sound don't show up reliably in studies until closer to 28 weeks. What that means in practice: your voice and your partner's voice can begin to register, but the inner-ear processing isn't dialed in yet.
The digestive system just started working, too. Your baby is swallowing amniotic fluid, processing it, and producing meconium. That's the dark, sticky first poop that won't show up until after birth.
Other quiet progress: motor control in the brain is increasingly sophisticated. Yawning, hiccupping, and grabbing the umbilical cord show up regularly on ultrasound.
Movements are getting stronger, even if you can't feel them yet. First-time parents typically don't recognize quickening until weeks 18 to 22.
Why your groin pulls when you stand up too fast
Sharp, pulling sensation in your lower belly or groin when you stand up, sneeze, or roll over in bed?
That's round ligament pain, per Cleveland Clinic.
The two rope-like ligaments that anchor your uterus are stretching to support your growing belly, and when you move suddenly, they pull faster than they're built to. It's common in the second trimester.
Not dangerous.
Briefly miserable.
What helps: rest, slow position changes, a warm bath, gentle stretching, an elastic belly band, and acetaminophen for severe twinges. Hold your belly when you sneeze. Roll out of bed sideways.
Your uterus is climbing fast right now. The top of it is roughly at the level of your belly button, and the bump is unmistakable in fitted clothes.
When to call your provider: pain that doesn't ease with rest, pain with vaginal bleeding or contractions, fever, or severe pain on one side that lasts more than a few hours.
The anatomy scan is the other big thing this week or next. ACOG's optimal window is 18 to 20 weeks because complex organs like the heart and brain image clearly at this stage. The scan runs 30 to 60 minutes.
The sonographer measures your baby's size, examines the heart chambers, brain, spine, kidneys, and limbs, checks the placenta and amniotic fluid, and can typically determine sex if you want to know.
For dads
Here's your move:
Talk to the bump this week. Your baby may start hearing sounds for the first time, and your voice will be one of the most familiar by the time they're born. You don't need a script. Read the news out loud while she's on the couch. Tell the bump about your day. Sing badly to a song you love in the car. It feels silly the first ten times you do it. Then it stops feeling silly. The point isn't to entertain a fetus. It's to start the lifelong habit of being a parent who narrates their world to their kid.
Real talk:
The anatomy scan is one of the most detailed looks you'll get at your baby before delivery, and it's also the appointment where they sometimes find things they want a closer look at. That happens. It's almost always followed by a follow-up that lands fine. Try not to spiral if the sonographer goes quiet for a stretch. They're concentrating, not signaling bad news. Be in the room. Hold her hand if she wants it. After the scan, talk about what you saw together. Naming the thing you both watched on the screen is one of those small acts that makes the pregnancy feel shared instead of separate.
Common concerns
Is it normal not to feel any movement at 18 weeks?+
Yes. Most first-time parents don't recognize quickening until weeks 18 to 22, with the average closer to 19 weeks per a 2022 study. If you haven't felt anything by 24 weeks, mention it to your provider.
What's the difference between round ligament pain and something more serious?+
Round ligament pain is sharp, brief, and triggered by sudden movements like standing up or sneezing. It eases with rest. Persistent pain, severe pain on one side, pain with bleeding, contractions, or fever are reasons to call your provider. Those signs can point to something else.
What if my baby can't hear yet at 18 weeks?+
There's no 'on switch' for hearing. The structures finish forming over weeks 16 to 22, and consistent fetal responses to external sound don't show up in studies until closer to 28 weeks. Talk and play music if you enjoy doing it.
Should we find out the sex at the anatomy scan?+
Personal call. Accuracy is high at the 18-22 week scan, especially after week 18. Some couples want the surprise at delivery. Others want time to settle on a name and decorate. Talk it through before the appointment so you're not deciding mid-scan.
Product picks for week 18
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BABYGO Birthing Ball with Pregnancy Yoga Book Set
Anti-burst birthing/exercise ball with a trimester-by-trimester pregnancy yoga book — the gentle stretching the round ligament pain section recommends.
Momcozy U-Shaped Pregnancy Pillow with Cooling Cover
Higher-tier 57-inch U-shape with a removable cooling cover — useful when blood-volume warmth makes the pillow feel hot.
KeaBabies Baby Sonogram Picture Frame (Alpine White)
Modern ultrasound photo frame designed to display the anatomy scan image on a shelf or wall — directly relevant to the scan happening this week or next.
Sources
- Mayo Clinic, Fetal Development: The 2nd Trimester (2025) — https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20046151
- ACOG, Ultrasound Exams (2024) — https://www.acog.org/womens-health/faqs/ultrasound-exams
- ACOG, How Your Fetus Grows During Pregnancy (2024) — https://www.acog.org/womens-health/faqs/how-your-fetus-grows-during-pregnancy
- Cleveland Clinic, Round Ligament Pain (2024) — https://my.clevelandclinic.org/health/symptoms/21642-round-ligament-pain
- Tveit JVH et al., Maternal perception of fetal movements: onset and associated factors, Journal of Perinatal Medicine (2022) — https://pubmed.ncbi.nlm.nih.gov/35779269/
A quick note: This content is for informational purposes only and is not a substitute for professional medical advice. Always talk to your healthcare provider about any questions or concerns. Content based on guidance from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), Mayo Clinic, and peer-reviewed medical literature. Learn how we create our content.