At five months pregnant, your baby is roughly 5½ to 7½ inches long (measured from head to bottom) and weighs between 7 ounces and 1 pound. That’s a dramatic range because growth accelerates quickly during this stretch. Five months of pregnancy corresponds to weeks 18 through 22, and your baby more than doubles in weight over those few weeks.
Week-by-Week Size at 5 Months
Because growth happens so fast during the second trimester, the difference between the start and end of month five is significant. Here’s what to expect at each milestone, measured from crown to rump (the top of the head to the bottom, since the legs are curled up):
- Week 18: About 5½ inches (140 mm) long, weighing around 7 ounces (200 grams)
- Week 20: About 6⅓ inches (160 mm) long, weighing around 11 ounces (320 grams)
- Week 22: About 7½ inches (190 mm) long, weighing around 1 pound (460 grams)
If you include the legs stretched out, total length from head to heel is closer to 10 inches by week 20. The crown-to-rump measurement is the standard one used in prenatal care because it’s more consistent. By week 19, your baby is about the size of an heirloom tomato. By the end of month five, think of a small papaya.
Weight gain during this period averages roughly 2 ounces per week, but it isn’t perfectly even. Your baby puts on fat more rapidly toward the end of the month as the body begins storing energy and filling out.
What’s Developing at 5 Months
Size isn’t the only thing changing. By week 17, just before month five begins, a waxy white coating called vernix starts forming over your baby’s skin. It acts as a barrier against the amniotic fluid, which would otherwise irritate the skin over months of constant exposure. Around the same time, fine, downy hair called lanugo covers the body. This peach-fuzz layer helps hold the vernix in place and keeps the baby warm.
By week 18, your baby’s movements become strong enough for you to feel them. Many first-time parents notice those initial flutters, sometimes described as bubbles or popcorn, somewhere between weeks 18 and 22. The baby is also developing the ability to hear sounds, yawn, and stretch. Facial features are becoming more defined, with eyebrows and eyelids now visible.
The 20-Week Anatomy Scan
The middle of month five is when most people have their detailed anatomy ultrasound, typically scheduled between weeks 18 and 22. This isn’t just a quick peek at the baby. It’s one of the most thorough exams of the entire pregnancy.
During the scan, the technician takes four core measurements: the width of the head, head circumference, abdomen circumference, and thigh bone length. Together, these confirm your baby’s size is on track for the gestational age. But the scan goes well beyond size. The technician examines the brain’s internal structures, the spacing and size of the eyes, the upper lip (to check for clefting), the chambers and valves of the heart, the spine in multiple views, the kidneys, bladder, and the point where the umbilical cord meets the abdomen.
All twelve long bones in the arms and legs are individually visualized. The heart gets special attention because it’s the most complex organ to assess at this stage. The examiner checks that it’s positioned correctly on the left side of the chest, that the four chambers look normal, and that blood is flowing through the major vessels properly. Heart rate is monitored throughout the scan to catch any rhythm irregularities.
For many parents, this appointment is also when they learn the baby’s sex, though the primary purpose is medical. If something looks unusual, you may be asked to come back for a follow-up scan or referred to a specialist.
How You Can Tell From the Outside
By 20 weeks, your uterus has grown enough that the top of it (called the fundus) reaches your belly button. This is a rough but reliable indicator that growth is progressing normally. After 20 weeks, your healthcare provider may start measuring the distance from your pubic bone to the top of the uterus at each visit. The measurement in centimeters generally matches the number of weeks you are, so at 20 weeks, it should be close to 20 centimeters.
This is also the point in pregnancy when the bump becomes hard to conceal. The baby, the placenta, increased blood volume, and amniotic fluid all contribute to noticeable growth in your midsection. Many people gain about 1 pound per week during the second trimester, though this varies widely and depends on your starting weight and overall health.
Why Size Can Vary
The measurements listed above are averages. Healthy babies at 20 weeks can weigh anywhere from 9 to 13 ounces and still be perfectly on track. What matters more than any single measurement is the growth pattern over time. A baby who consistently measures in the 25th percentile is just as healthy as one in the 75th, as long as growth follows a steady curve.
Factors that influence fetal size include genetics (taller parents tend to have longer babies), the number of previous pregnancies, the parent’s nutrition and blood flow to the placenta, and whether the pregnancy involves one baby or multiples. Twins and triplets are typically smaller at each stage, which is expected. If your provider notices that growth has stalled or jumped unexpectedly, they may order additional ultrasounds to monitor things more closely.