Fetus size by week: Your baby's weight throughout pregnancy (2023)

Find out how big your baby is during each week of their development with our fetal growth chart. From early in pregnancy, babies grow at different rates, so your baby's actual size by week may vary substantially – but look how they grow! At 20 weeks your baby may be just over 10 inches long and weigh less than 12 ounces, but by 32 weeks they'll reach almost 17 inches and top 4 pounds. At 33 weeks they may be over 17 inches and closer to 5 pounds, and by 37 weeks they'll reach 19 inches and about 6.5 pounds.

How do you determine fetus size by week?

There are different methods for estimating how big a fetus is, which is why you'll find different numbers depending on the source.

Experts have formulas they use to come up with the estimated fetal weight (EFW) and height of a fetus, and the formulas aren't always the same. The measurements that are used in equations to estimate weight usually include biparietal (head) diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur (thigh bone) length (FL).

Height is a straightforward measurement, but the method of measuring it changes after the first trimester. For the first 13 weeks, the height measurement is taken from the top of the head to the baby's bottom. After the first 13 weeks, the measurement is taken from the top of the head to the baby's heel – explaining why, on the chart below, your baby appears to grow 3 inches from week 13 to week 14!

Hadlock, the main source we use in our fetal growth chart, provides one of the most commonly used – and most accurate – equations for estimating fetal height and weight. The American College of Obstetrics and Gynecology (ACOG) and the Society for Maternal and Fetal Medicine (SMFM) use Hadlock's figures to diagnose and manage fetal growth conditions, such as intrauterine growth restriction (IUGR).

The numbers on our chart should coincide with the numbers your healthcare provider will be checking against when they measure your baby using ultrasound. (Providers don't measure height after 13 weeks, however, so don't expect to get those numbers at your ultrasound appointments.)

(Video) How to Increase Fetal Weight During Pregnancy

Note that the data used by Hadlock was gathered from middle-class Caucasian women with no history of maternal diseases known to affect fetal growth and no evidence of congenital anomalies. Your provider may make adjustments based on your individual circumstances.

Fetal growth chart

Wondering how big your baby is during each week of pregnancy? The numbers in our chart below can give you a sense of your baby's size. Keep in mind that your baby may be much smaller or larger than these averages. That's okay – after all, healthy babies can weigh less than 5 pounds or more than 9 pounds at birth.

(Video) Pregnancy Week By Week || 1 - 41 Weeks Fetal Developments

Boy's measurements are different than girl's measurements, even this early. For the numbers on our chart, we've taken an average of boys and girls. And remember, the height measurements up to 13 weeks are head-to-bottom estimates, while the height measurements starting at week 14 are head-to-toe estimates.


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(Video) Pregnancy Week-By-Week 🌟 Weeks 3-42 Fetal Development 👶🏼

Gestational ageLength (US)Weight (US)Length (cm)Mass (g)
(head to bottom)(head to bottom)
8 weeks0.62 inches0.71 ounces1.57 cm20 grams
9 weeks0.91 inches0.95 ounces2.30 cm27 grams
10 weeks1.22 inch1.23 ounces3.1 cm35 grams
11 weeks1.61 inch1.59 ounces4.1 cm45 grams
12 weeks2.13 inches2.05 ounces5.4 cm58 grams
13 weeks2.64 inches2.58 ounces6.7 cm73 grams
(head to toe)(head to toe)
14 weeks5.79 inches3.28 ounces14.7cm93 grams
15 weeks6.57 inches4.13 ounces16.7 cm117 grams
16 weeks7.32 inches5.15 ounces18.6 cm146 grams
17 weeks8.03 inches6.38 ounces20.4 cm181 grams
18 weeks8.74 inches7.87 ounces22.2 cm223 grams
19 weeks9.45 inches9.63 ounces24.0 cm273 grams
20 weeks10.12 inches11.68 ounces25.7 cm331 grams
21 weeks10.79 inches14.07 ounces27.4 cm399 grams
22 weeks11.42 inches1.05 pounds29.0 cm478 grams
23 weeks12.05 inches1.25 pounds30.6 cm568 grams
24 weeks12.68 inches1.48 pounds32.2 cm670 grams
25 weeks13.27 inches1.73 pounds33.7 cm785 grams
26 weeks13.82 inches2.01 pounds35.1 cm913 grams
27 weeks14.41 inches2.33 pounds36.6 cm1055 grams
28 weeks14.80 inches2.67 pounds37.6 cm1210 grams
29 weeks15.47 inches3.04 pounds39.3 cm1379 grams
30 weeks15.95 inches3.44 pounds40.5 cm1559 grams
31 weeks16.46 inches3.86 pounds41.8 cm1751 grams
32 weeks16.93 inches4.30 pounds43.0 cm1953 grams
33 weeks17.36 inches4.77 pounds44.1 cm2162 grams
34 weeks17.84 inches5.24 pounds45.3 cm2377 grams
35 weeks18.23 inches5.72 pounds46.3 cm2595 grams
36 weeks18.62 inches6.20 pounds47.3 cm2813 grams
37 weeks19.02 inches6.68 pounds48.3 cm3028 grams
38 weeks19.41 inches7.13 pounds49.3 cm3236 grams
39 weeks19.72 inches7.57 pounds50.1 cm3435 grams
40 weeks20.08 inches7.98 pounds51.0 cm3619 grams
41 weeks20.39 inches8.35 pounds51.8 cm3787 grams

Thanks to Dr. Mark Curran, maternal-fetal medicine specialist, for his help preparing this chart.

Fetal weight by week: How it changes

Your baby steadily gains weight over the course of your pregnancy, but it's not always at the same rate. If you're having one baby (not twins or multiples), your baby's rate of growth accelerates until 35 weeks, then decelerates.

Here are some highlights, based on estimations:

  • Up until 16 weeks, a fetus grows an average of about 19 grams per week, gradually increasing from 7 grams per week at 8 weeks to 15 grams per week at 12 weeks and 29 grams per week at 16 weeks.
  • By 20 weeks, a fetus is gaining about 59 grams per week (just over 2 ounces).
  • By 30 weeks, a fetus is gaining about 175 grams each week (more than 6 ounces).
  • At 35 weeks, a fetus is gaining about 215 grams each week, or about 7.5 ounces. At this point their growth rate peaks.
  • After 35 weeks, growth slows to about 188 grams per week, or 6.6 ounces. (Twins slow earlier, at around 28 weeks, and then average about 170 grams each week.)
  • In the last few weeks of pregnancy, the growth rate continues to gradually slow to about 168 grams (a little less than 6 ounces) per week by week 40.

Using a tape measure stretched over your belly, your provider will use a fundal height measurement to check your baby's size at your prenatal visits. Beginning at about 24 weeks, the measurement in centimeters should roughly match the gestational age of your baby. If you're 26 weeks pregnant, for example, your fundal height should be about 26 cm, give or take a centimeter in each direction.

If your provider is concerned that your baby is too small, they'll monitor your baby's size with ultrasound, which is more accurate. Using ultrasound, your practitioner can take various measurements (head circumference and diameter, abdomen circumference, femur length) and use them to estimate your baby's size. They may also use a Doppler ultrasound to look at the blood flow to your placenta.

If your baby's estimated weight is less than the 10th percentile for their gestational age, they may be diagnosed with intrauterine growth restriction (IUGR), also called fetal growth restriction (FGR). IUGR can happen at any time during pregnancy. Some babies with IUGR just turn out to be small for their age, but sometimes there's a problem that's preventing the baby from growing properly.

(Video) Is fetal weight as 228 gm normal in 8th month of Pregnancy? - Dr. Nupur Sood

At birth, a baby with IUGR is called "small for gestational age." While most SGA babies who are otherwise healthy grow just fine, some (especially those born prematurely) are at higher risk of problems such as c-section, jaundice, low blood sugar, and even long-term developmental and health problems.

Your baby's size by week

Here are some highlights of your baby's growth during pregnancy:

At 20 weeks, about the midpoint in your pregnancy, your baby is transmitting taste signals to their brain. And you may feel them hiccupping. Your baby's weight at 20 weeks is about 11.68 ounces, and they're about the length of a (10.12-inch) banana.

At 32 weeks, your baby's lungs are developing fast, and your baby's storing minerals like iron for their first 6 months of life. Your baby's weight at 32 weeks is 4.30 pounds, and their length is 16.93 inches, about the size of a jicama.

At 33 weeks, things are getting snug in there! Your baby's skin is becoming less wrinkled as they fill in – your baby's weight at 33 weeks is about 4.77 pounds. At 17.36 inches, your baby is now about the size of a pineapple.

At 37 weeks, your baby's brain and lungs are still maturing, and they're still moving a lot, despite the close quarters. Your baby's weight at 37 weeks is about 6.68 pounds, and they're about the length of a bunch of Swiss chard, 19.02 inches.

(Video) Your Growing Baby's Changes in the Third Trimester

Once your baby is born, they'll be weighed and measured, and your provider will continue to monitor their growth. While the average newborn weight is a little over 7 pounds, most newborns lose about 5 to 10 percent of their weight in the first days. No worries – they gain it back by the time they're about 2 weeks old, and by 4 months they usually double their birth weight.

Learn more:

  • To-do lists for the first, second, and third trimesters
  • Pregnancy Due Date Calculator
  • Pregnancy Weight Gain Calculator
  • How to understand pregnancy weeks, months, and trimesters


Fetus size by week: Your baby's weight throughout pregnancy? ›

Week 32: Baby practices breathing

By now your baby might be 11 inches (280 millimeters) long from crown to rump and weigh 3 3/4 pounds (1,700 grams).

What is the average fetal weight week by week? ›

Fetal growth chart: eight to 19 weeks of pregnancy
Pregnancy weekAverage Length (cm)Average Weight (g)
14 weeks8.7cm43g
15 weeks10.1cm70g
16 weeks11.6cm100g
17 weeks13cm140g
8 more rows

How much should a 32 week fetus weigh? ›

Week 32: Baby practices breathing

By now your baby might be 11 inches (280 millimeters) long from crown to rump and weigh 3 3/4 pounds (1,700 grams).

How much weight does baby gain in last 4 weeks? ›

The baby is still growing rapidly and could gain as much as an additional two pounds during the last four weeks of pregnancy.

Does a fetus double in size every week? ›

Month Two: While still small, baby is growing at a rapid pace; about a millimetre every day and doubling in size weekly. In week five, it will be around the size of lentil (5 mm); a raspberry in week seven; and by the end of the month the size of a kidney bean (about 1.6 cm).

What is the fetal weight chart? ›

The fetal weight chart is a tool that can be used to help estimate the weight of a fetus during pregnancy. The chart is based on data from a large number of pregnancies, and includes information on average fetal weights at different gestational ages.

Can you predict how much your baby will weigh? ›

Although methods exist to estimate birth weight, it is difficult to accurately predict a baby's weight before birth. As my patients approach their final weeks of pregnancy, they typically start asking questions about how much the baby will weigh and what that means for delivery. Doctors think about this too.

Is it normal for a baby to be 4 pounds at 32 weeks? ›

Week 32. Baby: Your baby measures about 18.9 inches long from head to toe and weighs almost 4 pounds. At this stage, they grow faster than ever. Baby fills almost all the space in your uterus now but may still have enough room to do somersaults.

When does a fetus gain the most weight? ›

During the final months of pregnancy, your baby gains the most weight. In fact, according to the American Pregnancy Association, a fetus weighs around 2 pounds at 27 weeks, 4 to 4 ½ pounds by 32 weeks, and grows up to between 6 ¾ pounds to 10 pounds, if you have a full-term delivery.

Are babies fully developed at 34 weeks? ›

By the 36th week, a baby's body is fully formed, and they're mostly just getting big enough to survive outside the womb. At 34 weeks, many of the baby's bodily systems aren't mature enough, especially the lungs. Lungs don't reach their full formation until around 36 weeks.

What is the last organ to develop in a fetus? ›

Almost all organs are completely formed by about 10 weeks after fertilization (which equals 12 weeks of pregnancy). The exceptions are the brain and spinal cord, which continue to form and develop throughout pregnancy.

What should I avoid at 35 weeks pregnant? ›

Limit caffeine to less than 200 milligrams each day. Limit your intake of fish to 2 servings each week. Choose fish low in mercury such as canned light tuna, shrimp, salmon, cod, or tilapia. Do not eat fish high in mercury such as swordfish, tilefish, king mackerel, and shark.

Will eating more help my baby gain weight? ›

To support all this growth, your doctor may advise you to increase your food intake. According to the American Pregnancy Association, your baby gains around 1/2 pound (266.6 gms) each week during the 9th month of pregnancy.

What is normal weekly baby weight gain? ›

Breastfed babies vs. formula-fed babies
Baby's ageAverage weight gain in ouncesAverage weight gain in grams
5 days to 4 months5–7 ounces per week170 grams per week
4 months to 6 months4–6 ounces per week113–150 grams per week
6 months to 12 months2–4 ounces per week57–113 grams per week
Aug 28, 2020

What is the average weight of a 35 week fetus? ›

Your baby weighs nearly 2.5 kilograms (5.5 pounds) and is almost 47 centimetres (18.5 inches) long.

What is a healthy fetal weight at birth? ›

Most babies born between 37 and 40 weeks weigh somewhere between 5 pounds, 8 ounces (2,500 grams) and 8 pounds, 13 ounces (4,000 grams).

What is the expected fetal weight at 37 weeks? ›

At 37 weeks, your pregnancy is considered full-term. The average baby weighs around 3-4kg by now.


1. 9 Months In The Womb: A Remarkable Look At Fetal Development Through Ultrasound By PregnancyChat.com
2. Intrauterine Growth Restriction in Pregnancy | Signs of Baby not growing in Uterus-Dr. H S Chandrika
(Doctors' Circle World's Largest Health Platform)
3. Is 30 weeks of fetal femur growth in 31 week pregnancy scan normal? - Dr. Teena S Thomas
(Doctors' Circle World's Largest Health Platform)
4. Baby | 5 Weeks baby in mother's womb | Pregnancy | Fetus development
(MedGram Health)
5. Your Growing Baby's Changes Through the Second Trimester | WebMD
6. Pregnancy Weeks To Months // 1 To 9 Weeks Fetal Developments
(Surgical Knowledge)


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