Fetal Growth Tracker
Enter gestational week to see expected fetal measurements.
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Fetal Growth by Week (50th Percentile)
| Week | Length (in) | Weight | Size of... |
|---|---|---|---|
| 12 | 2.1" | 0.5 oz | Lime |
| 16 | 4.6" | 3.5 oz | Avocado |
| 20 | 6.5" | 10.6 oz | Banana |
| 24 | 11.8" | 1.3 lb | Corn ear |
| 28 | 14.8" | 2.2 lb | Eggplant |
| 32 | 16.7" | 3.75 lb | Squash |
| 36 | 18.7" | 5.8 lb | Honeydew |
| 40 | 20.2" | 7.6 lb | Watermelon |
Fetal Growth Week by Week
Fetal growth follows a predictable curve. By 12 weeks, the baby is about 2 inches long. By 20 weeks (the halfway point), about 6.5 inches. At full term (40 weeks), the average baby is about 20 inches and 7.5 pounds.
These are 50th percentile values — half of babies are larger, half smaller. Your provider uses ultrasound to track your specific baby's growth curve.
Fetal measurements are reported by ultrasound as: BPD (biparietal diameter — head width), HC (head circumference), AC (abdominal circumference), and FL (femur length). These are used to calculate estimated fetal weight (EFW) using formulas like Hadlock: log₁₀(EFW) = 1.326 − 0.00326 × AC × FL + 0.0107 × HC + 0.0438 × AC + 0.158 × FL.
Growth percentiles: EFW is plotted against gestational age percentile charts (Hadlock, Fenton, INTERGROWTH-21st). The 10th–90th percentile range is considered normal. Below 10th percentile may indicate intrauterine growth restriction (IUGR); above 90th may indicate large for gestational age (LGA), associated with gestational diabetes and other factors.
Measurement accuracy: ultrasound EFW has a margin of error of approximately ±15–20% at term. A baby estimated at 8.0 lbs could weigh anywhere from 6.4 to 9.6 lbs at birth. Accuracy is higher earlier in pregnancy and when growth is on a consistent trajectory. Single measurements are less predictive than serial measurements showing the growth trend.
Crown-rump length (CRL): in the first trimester (6–14 weeks), CRL is the primary measurement for dating and is accurate to within ±5–7 days for gestational age estimation. After 14 weeks, HC and FL are used. After 28 weeks, ultrasound dating accuracy decreases — 12-week dates should be used as the primary reference if available.
Ultrasound measurements should be interpreted by a qualified healthcare provider, not self-diagnosed from a calculator.
See also: Due Date Calculator · Pregnancy Weight Gain Calculator