1st Trimester

Pre-Fertilization: how an egg gets ready to be fertilized.

Once a month one of a woman’s 2 ovaries release a mature egg, this is called ovulation. Ovulation happens approximately 2 weeks after the start of the woman's most recent menstrual period. The egg at this point travels into the woman’s Fallopian tube where it can be fertilized by a single sperm.

Fertilization: sperm and its journey to the egg

To begin the male ejaculates releasing approximately 40 million to 150 million sperm into the vagina, there the sperm travel upwards towards the woman’s reproductive tract. The sperm swim towards the Fallopian tubes from the vaginal opening, this can take from 30 minutes to even days for some sperm.

Interesting Fact: Inside of the vagina, sperm can live for up to 48 to 72 hours and out of the millions of sperm only a few hundred even come close to the egg.

Fertilization: Sperm Penetrates the Egg

Once both an egg and sperm are in the Fallopian tube the egg releases a chemical which attracts the sperm towards it. The sperm travels towards the egg and when the first sperm penetrates the egg, the egg’s surface changes to prevent entry from any other sperm. This process —which is called fertilization— takes around 24 hours, and it is at this time that the baby's sex will be decided by what genes the sperm is carrying.

Interesting Fact: If an egg is not already in the Fallopian tube, the sperm will stop moving and wait until the egg moves in before continuing its journey. Unlike other parts of the female reproductive tract the Fallopian Tubes provide the sperm with an environment where they can live up to 5 days.

After Fertilization: A baby’s beginning.

In this stage the fertilized egg starts to divide rapidly into new cells, to make room for this new growth the egg moves from the Fallopian tubes and into the uterus, this process usually takes 3 to 4 days.

Interesting Fact: If the fertilized egg does not enter the uterus properly a tubal or ectopic pregnancy can occur, in the case of an ectopic pregnancy the mother’s health will be at serious risk.

Implantation and Fetal Development

During implantation the fertilized egg attaches to the Endometrium —The lining tissues of the uterus— and continues to divide. After implantation in the uterus the cells will start forming different parts necessary for the babies development. Some cells will form the placenta and others will remain in the embryo to continue developing.

Interesting Fact: The hormones used to test for pregnancy in women are called Human Chorionic Gonadotrophin (HCG), these hormones were produced by the cells that later changed into the baby’s placenta.

1st Trimester (after fertilization)

3 weeks

Now inside of the woman is a microscopic ball of hundreds of rapidly multiplying cells that will develop into the baby. This ball is called a Blastocyst and is producing HCG to tell the ovaries to stop producing eggs.

poppy seed

4 weeks

The Blastocyst or ball of cells is now officially called an embryo. The woman is now about 4 weeks from the beginning of the last menstrual cycle. Around this time is when the next menstrual cycle should have started and pregnancy tests can be effective for telling if a woman is pregnant. The baby is the size of a poppy-seed.

sesame seed

5 weeks

The baby’s appearance is more similar to a tadpole then a human at this point but it is growing fast. The heart will begin beating this week and a circulatory system will start to form. The baby is the size of a sesame seed.


6 weeks

The baby’s facial features (nose, mouth, and ears), brain, and intestines are beginning to develop. The baby is now the size of a lentil.

blue berry

7 weeks

The baby still has a tail but its size has doubled since last week and the tail will soon disappear. Arms and legs begin developing alongside of hands and feet which resemble paddles in shape. The baby is now the size of a blueberry.


8 weeks

The baby begins moving around but not enough for the mother to feel it yet. Primitive neural pathways are formed from Nerve cells branching out. The lungs have begun developing alongside of breathing tubes in the throat. The baby is now the size of a kidney bean or about ½ an inch long.


9 weeks

The baby’s embryonic tail has disappeared and most of it’s basic physiology is in place (earlobes, nose, mouth, and more). The baby’s weight is a fraction of an ounce and is the size of a grape.


10 weeks

The baby has translucent skin and limbs that can bend, finer details like nails are starting to form. The baby is the size of a kumquat.


11 weeks

The baby has almost fully formed, movement from limbs stretching and kicking are now happening. The diaphragm is developing and can even produce hiccups. The baby is the size of a fig.


12 weeks

The baby’s reflexes begin working, fingers and toes will open and close and the baby’s mouth will make sucking movements. At this time the baby can feel a poke from the outside of the stomach, but the mother will not be able to feel the baby’s movements yet. The baby is the size of a lime.

pea pod

13 weeks

The baby’s fingers now have fingerprints and the veins and organs can clearly be seen through the skin. The baby is the length of a pea pod.

Interesting Fact: at week 13, if the baby is female, her ovaries will contain more than 2 million eggs at this developmental stage.

2nd Trimester


14 weeks

The baby can now use facial muscles, brain impulses have begun firing, and the babies kidney are now working. The baby is the size of a lemon.

Interesting Fact: At week 14 some babies have been seen sucking their thumb through the ultrasound. At week 15 if a flashlight is shined on the mother’s belly, the baby inside will move away from the beam.

15 weeks

The baby can sense light but the eyelids are still fused shut. At this week ultrasounds may reveal the sex of the baby and the baby is now the size of an apple.


16 weeks

The baby’s hair isn’t visible yet but patterning on the baby scalp has begun for it to start growing. The baby’s legs are more developed and moving, the head is more upright and the ears are almost in their final position. The baby is the size of an avocado.


17 weeks

The baby’s formerly soft cartilage is now hardening into bone, the umbilical cord is growing stronger and thicker and the baby can now move its joints. The baby is the size of a turnip.

bell pepper

18 weeks

The baby is forming an internal protective coating of myelin around its nerves and the baby’s body is more prone to moving around. The baby is now the size of a bell pepper.

heirloom tomato

19 weeks

The baby is developing its sense of smell, vision, taste, touch, and hearing now. The baby is now the size of an heirloom tomato


20 weeks

The baby’s digestive system is now producing Meconium (an early form of poop). The baby is now the size of a banana.


21 weeks

The baby’s movement has changed and becomes stronger with kicks and jabs against the walls of the womb. The baby is the length of a carrot.

Interesting Fact: Starting around week 21 when the babies movement becomes stronger some mothers start to recognize patterns of movement from their baby.
spaghetti squash

22 weeks

The baby’s features are now more distinct, such as lips and eyebrows have more definition. The baby is now the size of a spaghetti squash.


23 weeks

The baby is now the size of a large mango.

Interesting Fact: At 23 weeks the baby’s ear have now become adjusted to hearing sounds and some sounds after birth will be recognized from the time spent in the womb.

24 weeks

The baby is long and slim in its figure but the skin is still thin and translucent. The baby is now the size of an ear of corn.


25 weeks

The baby is starting to fill in its wrinkly skin with baby fat and resembling more of a newborn. The baby’s hair is starting to come in and have both color and texture. The baby now weighs around the same as an average rutabaga.


26 weeks

The baby inhales and exhales amniotic fluid, this helps develop the lungs in preparation for birth when the baby will have to breathe air. The baby is now the size of a bunch of scallions.


27 weeks

The baby has now developed a circadian rhythm for sleeping and its brain is very active. The baby is now the size of a head of cauliflower.

Interesting Fact: at week 27 the baby’s lungs aren’t fully formed, but if an early birth occurs the lungs can still function with medical help.

3rd Trimester


28 weeks

The baby has started developing eyesight allowing more light recognition, it’s eyelids can now blink and the eyelashes are fully grown. The baby is now the size of a large eggplant.

butternut squash

29 weeks

The baby’s head is growing larger for it’s developing brain, muscles and lungs are preparing for life outside the womb. The baby is now the size of a butternut squash.


30 weeks

The baby is still growing there is only 1 and ½ pints of amniotic fluid surrounding it now. The baby is the size of a large cabbage.


31 weeks

The baby now has enough control and strength to move its head from side to side, a layer of protective fat has developed throughout its body. The baby is now the size of a coconut.


32 weeks

The baby is now going to start gaining ⅓ to ½ of its birth weight in the next seven weeks. The baby is now the size of a large jicama.

Interesting Fact: The average baby’s mother gains about 1lb a week at this time but ½ of that goes to the baby.

33 weeks

The baby is now the size of a pineapple.

Interesting Fact: The baby’s skull won’t be fully fused until adulthood this allows the baby’s head to squeeze through the birth canal.

34 weeks

The baby’s lungs and central nervous system are maturing. The baby can now be born as long as there are no other health problems. The baby is now the size of a cantaloupe.

honeydew melon

35 weeks

The baby’s kidneys are now fully developed and the liver can process some waste products. The baby is now the size of a honeydew melon.

romain lettuce

36 weeks

The baby now gains about 1 once each day in weight. The Vernix Casosa, the waxy substance that used to protect its skin, is being shed. The baby is now the size of a head of romaine lettuce.

swiss chard

37 weeks

The baby’s lungs and brains begin their final maturation phase. The baby is now the size of a Swiss chard.


38 weeks

The baby is now the size of a leek.

Turning Full Term


39 weeks

The baby’s physical developments are complete and the baby is considered full term. The baby is now the size of a mini watermelon.


40 weeks

The baby is now the size of a small pumpkin.

41 weeks

The baby is now considered late-term. Health care practitioners will encourage the mother into inducing labor to avoid any health risks.