Fetus Growth & Pregnancy Symptoms Week by Week

First Trimester

Published : 02/05/2024

Last updated: 15/07/2024

The first trimester (week 0-13) is the most crucial and a time of rapid growth and development. Starting from the heartbeat, to the formation of the little one’s most vital internal organs and fingers and toes becoming distinctive.


For mothers, this is the time when you are introduced  pregnancy symptoms that includes breast tenderness, fatigue, nausea and vomiting, to a range of emotions starting from excitement to feeling anxious.


Here is a week by week brief overview, for the first trimester summing up your baby’s development and the expected symptoms that mothers are mostly facing during this time. All notes are kept simple with least bit of scientific details for the ease of understanding..


Now, you’ve probably discovered that you are pregnant and you may assume it’s your first week, but you’re likely already around 4 weeks pregnant. Its surprising we know – this is because healthcare providers calculate pregnancy from the first day of your last menstrual period (LMP). The normal time to conceive is about two weeks after that. 


During this first 2 weeks, your  body is priming for ovulation. By week 3 your body is laying the groundwork for placenta and fertilization. It is highly unlikely that you will notice that you are pregnant during this time.


At week 4 implantation occurs and the embryo starts to form. The placenta-produced hormone hCG (found in urine and bloodstream in pregnant mothers) reaches a detectable range by now and is high enough to be found in pregnancy tests. Hence, home pregnancy test kits starts showing positive for pregnancy (double lines) around this time.


So, lets start from here, all the cute baby details to a new mothers symptoms:

Pregnancy Week 4

Beginning in week 4 of pregnancy, the embryo is approximately the size of a poppy seed! Even though they are so tiny at this stage of pregnancy, their cells begin to form organs!


At this time each of these tiny life will start to make it presence felt within mothers and pregnancy symptoms might start showing…

Pregnancy Week 5

By the fifth week the embryo looks like a tadpole and is about the size of a sesame seed (yeah the little white seeds on top of buns).


The brain, heart, blood vessels, and spinal cord have all begun forming!

Pregnancy Week 6

By week 6, the embryo has grown to the size of a lentil. That’s approximately three times the size they were the week prior!


Heart tissue starts to develop and cardiac activity can be observed in the the lil one’s developing heart. 


You might not look pregnant yet but you’ll definitely start feeling like it from here, and these symptoms will ease up at the end of the first trimester – sore breasts, nausea, vomiting, constipation, exhaustion, headaches, faintness, heightened sense of smell and mood swings.

Pregnancy Week 7

At week 7, the lil one has doubled in size and is now the size of a blueberry.


The mouth, ears, eyes and nose will start looking more defined and arms and legs will form and look like tiny fins. 


For mothers, you might start feeling a bit of tightness in your clothes.

Pregnancy Week 8

At week 8, the embryo has grown a bit more and now its about the size of a kidney bean.


The tiny one will start forming webbed fingers inside their tiny limbs. Nerves, bones, and muscles will start developing as well.


You might start getting heavy morning sickness, increased vaginal discharge, and breast tenderness.


Pregnancy Week 9

At week 9, the lil one is officially a fetus and is growing rapidly. and is about the size of a large grape.


The lil one’s tiny fingers and toes are visible and taking shape. The facial features are now even more distinct, with eyelids fully formed but will remain shut until 27th week.


Some mothers will experience a decrease in nausea and vomiting symptoms. The uterus will start to develop in the lower abdomen.

Pregnancy Week 10

At 10 weeks, the fetus is on its growth sprout and is about the size of a strawberry.


The lil ones heartbeat can be heard on a fetal doppler. Inner ears are starting to form, finger and toenails can be seen appearing. And the fetus might start making tiny movements.


Your uterus is still about the size of a lemon but you might start noticing a tiny bump from here onwards.

Pregnancy Week 11

At 11 weeks the lil one is about the size of a fig  and making great progress.


The limbs have elongated and fingers are no longer webbed. Genitals will start to differentiate. it has started stretching but they are still unnoticeable until about 16 weeks.


Constipation and bloating are common during pregnancy mostly due to hormonal changes. Drink lots of water and exercise to keep things moving.

Pregnancy Week 12

The fetus is about the size of a lime at 12 weeks making impressive strides.


Around this time the fetus should be well formed with all major structures in place. Vital organs for example kidneys and digestive system will start to function.


Your uterus size is approximately equal to an orange. And your doctor should be able to feel the fundus. Also the chances of miscarriage has significantly reduced.

Pregnancy Week 13

The fetus is about the size of a lemon and finishing up its first trimester at 13 weeks.


The little one is busy developing vocal chords and maturing their nervous system around this time. The brain’s development is still in progress.


You have officially finished the first trimester and about to enter the second trimester next week! Congratulations!

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