Five months pregnant corresponds to roughly weeks 18 through 22, with most pregnancy calendars marking the end of week 20 as the halfway point of pregnancy and the completion of the fifth month. The confusion is understandable: pregnancy lasts 40 weeks but months don’t divide neatly into four-week blocks. Depending on which counting method your provider uses, you might see slightly different ranges, but weeks 18 to 22 is the most common window.
Why Weeks and Months Don’t Line Up Neatly
Pregnancy is tracked in 40 weeks starting from the first day of your last menstrual period. If months were exactly four weeks long, 40 weeks would equal 10 months, which obviously doesn’t match the “nine months” shorthand everyone uses. The gap exists because calendar months average about 4.3 weeks, not four. That extra fraction adds up over the course of a pregnancy.
Most providers and pregnancy resources place the fifth month between weeks 18 and 22. By the end of week 20, you’re roughly halfway through your pregnancy and about five months along. Some sources start the fifth month at week 17, others at week 18. The differences are small and mostly a matter of rounding. What matters more is your actual week count, which is what your care team uses for all scheduling and milestones.
How Big Your Baby Is at Five Months
Growth during this stretch is rapid. At week 18, the baby measures about 5.5 inches from head to bottom and weighs around 7 ounces. By week 20, that jumps to roughly 6.3 inches and 11 ounces. Those measurements are crown to rump only, not including the legs, so actual full length is several inches longer. Most people compare the size to a banana or a bell pepper around this stage.
The baby’s movements are becoming more coordinated, and if you haven’t already felt movement, the fifth month is when most people notice it for the first time. Those early flutters, sometimes called quickening, can feel like bubbles, light tapping, or a rolling sensation low in your abdomen. First-time parents often don’t recognize the movements until closer to week 20 or 21, while people who’ve been pregnant before may notice them a few weeks earlier.
The Anatomy Scan Happens Now
The biggest medical milestone during the fifth month is the 20-week ultrasound, commonly called the anatomy scan. This is the most detailed ultrasound of your entire pregnancy. A sonographer takes measurements and images of the baby’s heart, brain, spine, kidneys, bladder, lungs, stomach, intestines, limbs, hands, feet, and facial features. They also record the heart rate, check blood flow through the umbilical cord, measure your amniotic fluid levels, and look at the position of the placenta and the length of your cervix.
The appointment typically takes 30 to 45 minutes, sometimes longer if the baby isn’t in a cooperative position. This is also the scan where you can learn the baby’s sex if you want to know. If the sonographer spots anything that needs a closer look, you may be referred for a follow-up ultrasound, which doesn’t automatically mean something is wrong. Some structures are simply hard to see clearly depending on the baby’s position that day.
What You Might Be Feeling
By five months, your uterus has grown to roughly the level of your belly button, and the physical changes are hard to miss. Back pain is one of the most common complaints during this stretch. There are several reasons it ramps up now: hormones are loosening the ligaments in your pelvis and lower back to prepare for delivery, the extra weight in front of your body is pulling your center of gravity forward, and your abdominal muscles are stretching and weakening, which forces your back muscles to pick up the slack. If the baby happens to be positioned with their head pressing against your lower spine or tailbone, that can make things worse.
Other common symptoms at five months include nasal congestion (increased blood volume causes swelling in nasal passages), leg cramps, mild swelling in your feet and ankles, and skin changes like a darker line running down the center of your belly. Round ligament pain, a sharp or pulling sensation on one or both sides of your lower abdomen, is also typical as the ligaments supporting your uterus stretch.
Sleep Position Starts to Matter
Around 20 weeks, your uterus is large enough that lying flat on your back can compress major blood vessels, specifically the large vein that carries blood back to your heart and the main artery that sends blood to your lower body and the placenta. This doesn’t mean you’ll cause harm if you wake up on your back occasionally, but it’s a good time to start favoring side sleeping for the rest of the night.
Current guidance is reassuring: you don’t need to stay perfectly on your left side all night. Sleeping on either side provides good blood flow. Even propping yourself at a 20 to 30 degree angle with a wedge pillow is enough to relieve pressure if you tend to roll onto your back. A pillow between your knees can also help with the back and hip discomfort that tends to pick up during this stage.
A Quick Week-by-Month Reference
Since the weeks-to-months question comes up repeatedly throughout pregnancy, here’s a general guide for the second trimester:
- Month 4: Weeks 14 to 17
- Month 5: Weeks 18 to 22
- Month 6: Weeks 23 to 27
These ranges vary slightly depending on the source, so if your provider groups the weeks a little differently, that’s normal. The week number itself is always the more precise and useful measure. When someone asks how far along you are, leading with your week count gives the clearest answer.