What Is the Size of the Fetus at Each Stage?

What woman or man, after discovering a pregnancy, doesn’t try to imagine, based on the ultrasound measurements, the size of their little baby who is still a tiny fetus? What size is it now?? Is it the size of a thumb or a bean? Every week your baby will be a different size and yes, it can be compared to hundreds of things from around the world. Let’s start at the beginning of pregnancy:

4 weeks – At 4 weeks, the little baby is already considered an embryo. But inside the belly it is unnoticeable and on the ultrasound, practically impossible to see. In this week, its size can be compared to a tiny poppy seed. You know those tiny ones used to decorate sandwiches and petit-fours at bakeries? At this stage of pregnancy it is very common for the first pregnancy symptoms to show up and moms to discover they are pregnant.

5 weeks – In the 5th week your beautiful little baby still doesn’t look anything like that cute face that will be born. Right now, it looks more like a tadpole than a baby. In this week it is the size of a sesame seed, very tiny right? But it has already grown a bit since the previous week.

6 weeks – At 6 weeks, the embryo is growing more and more each day and since last week it has already doubled its size. This week, it can be compared to the size of a small lentil.

7 weeks – This week it is even bigger and doubles in size each week. This is the recommended time to have the first ultrasound and, when seen, it is compared to the shape of a bean. Its size at this moment is like a chickpea, which moves all the time inside the uterus, although still unnoticeable to the mother.

8 weeks – This week the little embryo gets a promotion and becomes a fetus! It has already grown even more and reaches the size of a single grape. The embryonic tail that made it look like a tadpole disappears at this stage, making way for the development of muscles, nerves and organs¹.

9 weeks – At 9 weeks, the fetus increasingly gains human features and its genitals are in full development, though it is not yet possible to detect from an ultrasound. At this stage, its size is compared to a Brazil nut.

10 weeks – Your future baby is getting stronger and chubbier every day, and at this stage measures about 3 centimeters. This week, its size is compared to an olive and it is already so active that it jumps and kicks all the time, even though the mother can’t feel it yet.

11 weeks – At 11 weeks, the fetus already has arms and legs formed and its tiny fingers are separated. Now it is about 4 centimeters long, being the size of a fig.

12 weeks – In the 12th week, it starts to look more and more like a baby. Its eyes are still far apart on its face, but will move into position over the next few days. It measures around 5 centimeters and is compared to a small lemon.

13 weeks – At this stage, it starts to stretch more and more, gaining size and weight. It weighs around 25 grams, being compared to half the size of a banana or the size of a green bean pod.

14 weeks – At 14 weeks, its body is growing faster than its head², which was previously out of proportion. At this stage, it’s starting to look more and more like the baby you will meet at birth. This week, it is the size of a lemon (Eureka lemon).

15 weeks – This week it will be even bigger, about the size of an apple and weighing on average 70 grams. At this phase, it often hiccups a lot, even though the mom can’t feel anything.

16 weeks – The weight gain is getting faster and so is the growth. This week, it weighs up to 100 grams and is 12 centimeters in length. It’s the size of a large pear.

17 weeks – In the 17th week, the fetus now weighs about 140 grams and can be compared to the size of a ginger root.

18 weeks – At this stage, it can already practice breathing, even if it can’t inhale air, only amniotic fluid. It’s practicing what it will need to do as soon as it’s born. Now, it’s about 14 centimeters long and weighs 200 grams, being the size of a bell pepper. Pretty big, right?

19 weeks – The fetus can now swallow amniotic fluid and consequently produce and pass urine, which proves that its kidneys are working properly. By now it’s 15 centimeters and is compared to the size of a coconut (dry coconut).

20 weeks – We’ve finally reached the halfway mark of pregnancy!! Now is a good time to find out the baby’s sex via ultrasound, but you’ll need the little baby’s cooperation for that! Now, it’s the size of a banana.

22 weeks – By now it already has just the features it will have at birth, though it’s still very skinny. From now on, it will start to gain weight until the end of pregnancy. Its weight averages 430 grams and it can be compared to the size of a carrot.

24 weeks – By this week its weight has increased quite a bit, reaching 600 to 650 grams and looking more and more like the baby that will be born in the coming months. Its size compares to an ear of corn.

26 weeks – At this stage, a very important milestone occurs: your baby can now open and close its little eyes, practicing for when it’s outside. It is already so big that it measures about 36 centimeters, the same size as a stalk of green onion.

28 weeks – The baby is getting more alert and responding to stimuli, especially to light on the belly. This week, it has reached 1 kg and measures about 38 centimeters, about the size of a small red cabbage.

30 weeks – This week its vision is more acute and it can already see what happens inside the womb. Growth slows down for the moment, but weight gain is in full swing. It is about 40 centimeters in size, about the size of a large cabbage.

32 weeks – Your baby has gotten chubbier, weighs about 1.7 kg, and is already as big as a pineapple.

34 weeks – The process of weight gain continues faster than in all previous stages because it will need a thick layer of fat to regulate its temperature outside³. At this point, it can be compared to a cantaloupe melon.

36 weeks – During this rapid phase of weight gain, it can put on up to 30 grams a day and already measures 45 centimeters. It’s as big as a head of romaine lettuce.

38 weeks – The baby is now full-term and can be born at any time. It already weighs around 3 kilos and is as large as a jackfruit. So big!!

40 weeks – If your baby hasn’t been born yet, it can happen any time and may come without warning. Weight and length vary greatly from baby to baby, but this week they usually weigh around 3.5 kg and measure 50 centimeters. Its size is similar to a small pumpkin.

It’s important to remember that babies do not all develop the same way and don’t follow strict rules. These measurements are just statistics and provide a rough idea of how your baby is developing during pregnancy. Accurate measurements should be assessed through ultrasound scans, and even then, remember that there is a margin of error in the test.

See also: Reference Table of Fetal Size and Weight During Pregnancy