At 22 weeks of pregnancy, a baby typically weighs about 1 pound (460 grams) and measures roughly 7.5 inches (190 millimeters) from crown to rump. That’s about the size of a sweet potato. Keep in mind that this is an average, and healthy babies at this stage can fall above or below that number.
How Baby’s Weight Is Estimated
You can’t step on a scale in the womb, so your provider estimates fetal weight using ultrasound measurements of the baby’s head, abdomen, and thigh bone. A formula combines those three numbers into an estimated weight. The most widely used version of this calculation carries a margin of error up to 20% in either direction, meaning a baby estimated at 460 grams could realistically weigh anywhere from roughly 370 to 550 grams and still be perfectly on track.
That margin matters. If your ultrasound report shows a weight slightly above or below the average, it may simply reflect the inherent imprecision of the measurement rather than an actual growth concern. Your provider looks at the overall trend across multiple appointments, not a single snapshot.
What’s Happening at 22 Weeks
Weight is only one piece of the picture. At 22 weeks, your baby’s eyebrows and hair are becoming visible. For boys, the testes have started descending into the scrotum. For girls, the uterus, ovaries, and vagina are already in place. The skin is still thin and somewhat translucent, but the baby is filling out and beginning to look more proportional.
This is also a period of rapid weight gain. During the second trimester, the baby is adding layers of fat and muscle at an accelerating pace, and by the time you reach full term, that 1-pound baby will have grown to an average of 7 to 8 pounds. The weeks ahead involve the most dramatic growth of the entire pregnancy.
What Affects Fetal Weight
Several factors influence how big or small a baby measures at 22 weeks. Genetics play a significant role: smaller parents tend to have smaller babies, and that’s perfectly normal. Beyond genetics, the placenta and umbilical cord are the baby’s lifeline. If the placenta doesn’t attach well or blood flow through the umbilical cord is limited, the baby may not receive enough nutrients to grow at the expected rate.
Maternal nutrition and weight gain also matter. Poor nutrition during pregnancy can slow fetal growth, while conditions like high blood pressure or diabetes can affect how efficiently the placenta delivers oxygen and nutrients. Chromosomal differences in the baby itself can sometimes influence growth patterns as well.
When Weight Falls Below the 10th Percentile
Doctors become concerned about fetal growth when the estimated weight drops below the 10th percentile for gestational age. This is called intrauterine growth restriction, or IUGR. In practical terms, it means the baby is smaller than 9 out of 10 babies at the same stage of pregnancy.
Your provider might first suspect a growth issue if your fundal height (the distance from your pubic bone to the top of your uterus) measures 4 centimeters or more below what’s expected. From there, a detailed ultrasound can estimate the baby’s weight and check other indicators. Low amniotic fluid volume and reduced blood flow through the umbilical cord, detected with a specialized Doppler ultrasound, can both point toward IUGR.
If growth restriction is identified, your provider will typically monitor the pregnancy more closely with repeat ultrasounds to track the baby’s growth trajectory and blood flow. Many babies with IUGR do well with careful monitoring, though the management depends on the underlying cause and how far along the pregnancy is.
Why 22 Weeks Is a Notable Milestone
Beyond weight, 22 weeks carries significance because it sits right at the edge of viability. A large study of births in England and Wales found that among babies alive at the onset of labor at 22 weeks, survival to discharge from neonatal care was about 8%. When babies at this age were admitted to a neonatal intensive care unit, roughly 3 in 10 survived to discharge. Of those survivors, about 36% did not have a major health complication at the time they left the hospital, though long-term outcomes remain uncertain.
These numbers have improved over time. The same study found that survival-focused care at 22 weeks increased threefold over recent years, driven largely by updated national guidelines encouraging active treatment at earlier gestational ages. Still, 22 weeks remains extremely early, and the outcomes underscore just how much critical development happens in the weeks that follow.
Putting the Numbers in Perspective
If your 22-week ultrasound shows a weight close to 1 pound, your baby is right where most babies are. If the number is a bit higher or lower, remember that ultrasound estimates are approximations, and a single measurement doesn’t tell the whole story. What matters most is the growth pattern over time. A baby consistently tracking along the 25th percentile, for example, is growing normally for their size, even though they’re smaller than average. The concern arises when a baby’s growth curve flattens or drops off from where it has been.
Your provider uses percentile charts that account for gestational age, and they’ll compare each new measurement against your baby’s own growth trend. If everything is tracking steadily, a weight that’s slightly above or below the textbook average is nothing to worry about.