Week 18 is a big week for many moms: if they’ve got their anatomy ultrasound scheduled during this week (some doctors prefer to wait until closer to 20 weeks for this, and that’s OK, too), they can finally tell the sex of their baby! However, this isn’t guaranteed, of course. Babies don’t always cooperate during the ultrasound.

Not every mom is on the same schedule, but in the second trimester, it’s typical to see your doctor or healthcare practitioner about every 4 weeks, which means there is usually an appointment somewhere between 16 and 18 weeks as well as a separate ultrasound appointment somewhere between 18 to 20 weeks. So if you don’t know already (and congratulations if you do!), and you’re planning on finding out, this is the week you may finally figure out how to decorate that nursery and start getting serious about names.

Your Body

So how’s your back feeling? If you’re beginning to experience dull back pain that can range in severity from mild to “I can’t get up,” don’t worry. This isn’t a sign of anything being seriously wrong (unless it is excruciating or persists) and likely isn’t even related to round ligament pain, which is a specific type of pain.

your body week to week 18

Instead, a number of changes are occurring in your pregnancy that cause back pain for up to 80 percent of expectant moms. First, there’s the obvious one: your uterus is now the size of a decent-sized water balloon, resting in your lower, front abdomen. This has not only changed your center of gravity—you might notice you’re thrown off balance more easily—but it’s putting added strain on the muscles and ligaments of your lower back. Additionally, your body is now ramping up production of a pregnancy hormone called relaxin. Just like the name sounds, this hormone is responsible for loosening your joints and ligaments. There are good reasons for this; it prepares your body for the truly hard work of carrying a large baby in the coming weeks. For now, though, it results in added back pain.

If this sounds like you, fortunately there are steps you can take, beginning with scheduling that massage. Now is the perfect time to get that prenatal massage or even press your partner or spouse into duty as an amateur masseuse. It also helps to get plenty of exercise, be careful with rapid weight gain, take lots of sit-down breaks, wear a supportive belly band, and with your healthcare provider’s permission, take painkillers like acetaminophen.

Now, about that ultrasound. Depending on your healthcare provider, you’ve likely had at least one ultrasound already. These are non-invasive tests that use sound waves to generate an image of your baby in the womb. There are various types of ultrasound; which one you get depends on your situation and healthcare provider’s preference.

As a final note, now that your baby is growing more rapidly, it’s especially important to continue with your prenatal vitamins. These vitamins include iron that moms-to-be need to both keep up their own red blood cell count and provide enough iron for their developing babies. If you’re experience odd symptoms like headaches, dizziness, and certain cravings, you may have an iron deficiency. Check with your doctor, however, before self-diagnosing and increasing your iron intake.

Your Baby

Your baby’s fetal age is now 16 weeks. He or she is roughly 5 to 5.5 inches long and weighs somewhere between 5–7 ounces. It varies, but your baby is roughly the size of a turnip now.

your baby week to week 18

Over the last few weeks, your baby has been growing very fast, roughly growing 50 percent by weight every week. This will continue for a while, but the rate will begin to slow as the weeks go on.

By now, your baby is looking very human. The ears have moved into their final positions, fingernails have formed, and the eyes are in position (although they are sealed shut until birth). Internally, the sexual organs have developed to the point that they are likely visible on ultrasound. For girls, the fallopian tubes and uterus have already formed. For boys, the penis is clearly formed and identifiable, even if he does hide it during the ultrasound.

Internally, your baby’s nervous system is developing now. The nerves are beginning to form their myelin sheathes. This special type of cell covers nerve cells and is crucial in transmitting signals between nerves. The rapid nerve development is coupled with more extensive brain development, as the nervous system begins to send more detailed information to the brain, allowing your baby to recognize and process more and more stimuli. In a very real way, your baby’s personality is already beginning to form!

One more neat thing: your baby is also learning to yawn at this point. If you’re lucky, you’ll catch a yawn on the ultrasound. No one knows why babies yawn—or adults, for that matter—but it can be great to see it.


Doctor Tip
“Women who exercise in pregnancy have shorter labors, lower chances of developing gestational diabetes or needing a C-section, and healthier babies.”

Read more doctor tips.

Reviewed by Dr. Jen Lincoln, November 2018


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