At 23 weeks of pregnancy, a baby typically weighs about 500 grams, or roughly 1.1 pounds. That’s about the size of a large mango. While this number gives you a useful benchmark, the actual weight of your baby can vary depending on genetics, sex, and several maternal health factors.
Average Weight and Length at 23 Weeks
The commonly cited average for a 23-week fetus is around 501 grams (1.1 pounds). Crown-to-heel length at this stage is approximately 28 to 29 centimeters, or about 11 inches. These numbers come from population-level growth charts, so they represent the midpoint of a wide range of healthy sizes.
Boys tend to be slightly heavier than girls at this stage. Canadian population data shows the 50th percentile weight for boys at 23 weeks is about 589 grams, compared to 557 grams for girls. That gap widens as pregnancy continues. The range of normal is broad: a boy at the 10th percentile weighs around 475 grams, while one at the 90th percentile reaches about 714 grams. For girls, that range runs from roughly 450 grams up to 669 grams. A baby falling anywhere within this spectrum is considered appropriately grown.
How Ultrasound Weight Estimates Work
If your provider gave you a weight estimate from an ultrasound, keep in mind that these measurements are educated approximations. The ultrasound technician measures the baby’s head circumference, abdominal circumference, and thigh bone length, then software calculates an estimated weight from those numbers. The accepted margin of error is up to 20% in either direction. That means a baby estimated at 500 grams could realistically weigh anywhere from 400 to 600 grams. This doesn’t mean the scan is unreliable. It simply means a single number shouldn’t cause alarm if it’s slightly above or below average.
Your provider also tracks fundal height, the distance from your pubic bone to the top of your uterus. At 23 weeks, this measurement should be close to 23 centimeters, plus or minus 2 centimeters. If the fundal height is consistently off from what’s expected, your provider may order additional ultrasounds to monitor growth more closely.
What Affects Your Baby’s Size
Several factors influence how much a baby weighs at any point in pregnancy. Some are out of your control: genetics plays a major role, and parents who are taller or larger-framed tend to have bigger babies. Whether this is your first pregnancy matters too. Women who have given birth before tend to have heavier placentas (by about 30 grams on average), which supports greater nutrient transfer and slightly larger babies.
Pre-pregnancy BMI and weight gain during early pregnancy also play a role. Research published in PLOS ONE found that weight gain in the first half of pregnancy had a stronger effect on placental growth than weight gain later on. This makes sense: the placenta is the supply line, and its size and function during the first 20 weeks sets the stage for how efficiently nutrients reach the baby in the second half of pregnancy. Fasting blood sugar levels also influence placental weight, particularly for mothers carrying girls.
Smoking, high blood pressure, and certain chronic health conditions can restrict blood flow to the placenta and slow fetal growth. On the other end, gestational diabetes can cause a baby to grow larger than average because of excess glucose crossing the placenta.
What’s Developing at 23 Weeks
Weight is only one piece of the picture at 23 weeks. This is a period of rapid development in several key systems. The lungs are beginning to produce surfactant, a substance that coats the inside of the air sacs and prevents them from collapsing. Without enough surfactant, a baby’s lungs can’t function independently, which is why every additional week of lung development before birth significantly improves outcomes.
Your baby has also started making rapid eye movements, a sign of increasing brain activity. The ridges that will become unique fingerprints and footprints are forming on the palms and soles. Skin is still thin and translucent at this stage but will thicken and gain fat stores over the coming weeks.
Why 23 Weeks Is a Critical Milestone
Many parents searching for weight at 23 weeks are also thinking about viability, the point at which a baby could survive outside the womb with intensive medical support. At 23 weeks, that threshold has just been crossed. A Stanford Medicine review of nearly 11,000 premature births found that 55% of babies born at 23 weeks survived. That’s a significant improvement over previous decades, driven by advances in neonatal intensive care.
Survival, however, is only part of the story. Among babies born between 22 and 26 weeks who were evaluated at age 2, about half showed mild or no signs of developmental problems. Around 29% had moderate disabilities, and 21% had severe impairments, including a small percentage with blindness, significant hearing loss, or cerebral palsy. About half of these extremely premature babies were rehospitalized at least once after their initial NICU stay.
These numbers improve with each additional week of pregnancy. A baby born at 24 or 25 weeks has substantially better odds than one born at 23, both for survival and for long-term health. This is one reason providers monitor fetal weight carefully during this period: if growth is on track, it’s a reassuring sign that the pregnancy is progressing well.
When Weight Falls Outside the Expected Range
If your baby’s estimated weight is below the 10th percentile, your provider may diagnose intrauterine growth restriction (IUGR). This doesn’t always indicate a problem. Some babies are constitutionally small, meaning they’re healthy but genetically programmed to be on the smaller side. In other cases, restricted growth points to an issue with placental function or blood flow that needs monitoring.
A baby measuring above the 90th percentile is considered large for gestational age. At 23 weeks, this finding often prompts screening for gestational diabetes, since elevated blood sugar is one of the most common treatable causes of accelerated fetal growth. In many cases, though, a large baby simply reflects parental size or normal variation.
Either way, a single measurement that’s slightly off the average rarely signals a concern on its own. Providers look at the trend over multiple visits. Consistent growth along the same percentile curve, whether that’s the 20th or the 80th, is more important than hitting one specific number at one specific week.