Zygote implants on wall of uterus. Organism now called an embryo. 

3 wks from LMP  
1 wk gestation  

Rapid growth - amniotic sac, amniotic cavity and yolk sac are developing.

The placenta begins to form and blood circulates within it. 

Chorionic villi, the tissue lining the placenta begins to develop.

Lunar Month 2 
2 wks gestation,  
4 wks LMP  

"Primitive streak" (forerunner of brain and spinal cord) is evident. Baby's head is now detectable.

A groove forms in primitive streak setting stage for three layers of tissue: ectoderm, mesoderm and endoderm. 

Ectoderm will form skin, hair, lining of ear, nose, mouth, glands and nervous system. 

From the mesoderm, baby will develop muscles, bones, blood cells, heart, lungs, excretory and reproductive systems.

From the endoderm, baby will develop lungs, tongue, glands, bladder and digestive tract. 

Next 10-30 days are crucial in nervous system and heart development.  
folic acid  
liquids 

3 wks gestation  
5 wks LMP  
Early heart beats. Facial features and lung buds begin to form. 

Evidence of eyes and inner ears. 

Nerual tube (later known as spinal cord) begins to fuse.

Tiny buds that will form the arms appear.

Lower limb buds appear. Eyes, liver and digestive system begin to form. 

4 wks gestation  
6 wks LMP  
Length of embryo measures 4 mm. 

Baby's eye lens pits, optic cups and nasal pits begin to form.

Primitive mouth appears. 

Baby's arms look like paddles. protein 

Length of embryo is now 7mm; 

The head is now much larger than trunk. Foot plates present. 

5 wk gestation, 7 wk LMP  
 Embryo is now 8 mm long. 

Oral and nasal cavities forming. Cerebellum and spleen begin to develop. 

Head to rump is now 9 mm. 

Baby's upper lip formed. 

Embryo is now 10 mm long. 

Baby's upper limbs bend at elbow; external ear beginning to form. 

Digital rays (early fingers) developing. 

Lunar Month 3  
6 wks gestation  
8 wk LMP  
Length of embryo is now 13-16mm (1/2 inch long). 

Eyelids beginning to form. 

Baby's tip of nose is now distinct. 

Buds of genitals begin. 

Baby's trunk is elongating and straightening. 

7 wks gestation  
9 wks LMP Length: 18-20 mm (3/4 inch).  
fetal heart beat 

Upper limbs longer and bent at elbows; fingers distinct. Baby's anal membrane now perforated; testes and ovaries distinguishable. 

Length of embryo is now 22-25 mm. 

External genitalia still in sexless state. 

Groove for urethra formed; anus formed. 

Baby's intestines have formed outside baby (on umbilical cord) because they can't fit inside.

8 wks gestation  
10 wks LMP  
Length: 30 mm (1 1/4 inch). 

Baby is free floating in amniotic fluid; fetus is moving but cannot be felt by mother. 

Baby is no longer an embryo; now begins the fetal period. 

Tiny phallus forms which could be penis or clitoris; perineum formed 

Urethral fold extends into phallus and genitalia now show male characteristics now if a boy. 

9 wks gestation  
11 wks LMP  
Lenth of fetus: about 5 cm (almost 2 inches). Weight: about 8 grams.

Iris is forming: Eyelids will temporarily fuse shut.

Face now has a human profile and prominent chin. 

Clitoris in female formed; labia majora formed. 

Glans penis and scrotum formed. 

10 wks gestation  
12 wks LMP  
Length: 6.1 cm (almost 2 1/2 inches). Weight: about 14 gm. 

Urine is formed and discharged into the amniotic cavity. 

Coils of baby's intestine visible. 

Fetus is swallowing and absorbing fluids. 

Early fingernails are developing. 

11 wks gestation  
13 wks LMP  
Length: 7 cm crown to rump (9 cm from head to toe). Weight: about 30 gm or 1 oz.

Intestines are now contained within the abdomen. 

Vocal cords develop

12 wks gestation  
14 wks LMP  
Length: 8.7 cm crown to rump (11 cm or 4 1/2 inches head to toe). Weight: 45 gm. 

13 wk gestation  
15 wk LMP  
Beginning of Second Trimester. Length: 10 cm crown to rump (12.5 cm head to toe); Weight: 80 gms (1 1/2 ounces). 

Period of rapid growth begins. 

The uterus is approx. half way from pubic bone to umbilicus. 

14 wk gestation  
16 wk LMP  
Length: 12 cm crown to rump (14 cm or 5 1/2 inches head to toes). Weight: about 3 ounces. 

Limb movements become coordinated. Head is now erect.

Eyes are now more forward rather than to side of head. Slow eye movements begin. 

Baby continues to grow rapidly; adds blinking to its list of refluxes (sucking, swallowing are others).

Early toenail development. 

15 wk gestation  
17 wk LMP  
Length: 13 cm crown to rump (16 cm or 6 1/4 inches head to toe). Weight: about 155 gms (4-5 oz)

16 wks gestation  
18 wks LMP  
Length: 14 cm crown to rump (18 cm or 7 inches head to toe). Weight: about 200 gm. 

Baby's body growth is now catching up to his/her head. 

Baby's lower limbs lengthening and bones are becoming ossified.

If baby is a girl, early ovaries contain early follicles with early eggs. 

Ears almost close to their position at side of head and stand out from head.

17 wks gestation  
19 wks LMP  
Length: 15 cm crown to rump (20 cm or 8 inches head to toe). Weight: about 240 gm or 8 oz.

Growth slowing a bit.

18 wks gestation  
20 wks LMP  
Length: 16 cm crown to rump (25 cm or 9 3/4 inches head to toe). Weight: 300 gm or 10 oz. 

Baby's skin is coated with a cheesy substance (vernix) which protects against chapping, abrasions, and hardening. 

If baby is a girl, the uterus is formed and development of vagina has begun.

19 wks gestation  
21 wks LMP  
Length: 17.5 cm crown to rump. Weight: 390 gm or 14 oz.  halfway !

20 wks gestation  
22 wks LMP  
Length: about 19 cm crown to rump (27 cm or 10 1/2 inches head to toe). Weight: about 1 lb.

Fine downy hair called lanugo now covers baby's body; eyebrows are visible.

Brown fat developed - this specialized fatty tissue keeps  baby warm.

Testes in boys begin to descend; Ovaries in female located against posterior abdominal wall.

21 wks gestation  
23 wks LMP  
Length: 20 cm crown to rump (28 cm or 11 inches head to toe). Weight: about 500 gm.

Rapid eye movements begin. 

Baby is better proportioned. 

22 wks gestation  
24 wks LMP  
Length: 21 cm crown to rump (29 cm or 11 1/4 inches head to toe). Weight: 630 gm.

Baby's skin is wrinkled, translucent, and pink to red. If you could see your baby, you could see her bones, organs and vessels.

23 wk gestation  
25 wk LMP  
Length: 22 cm crown to rump (30 cm or 11 3/4 inches head to toe). Weight: about 700 gm.

Baby's bowel contains some meconium, a dark green tar-like substance excreted during the first few days after birth. 

The linea nigra, a black line, might appear from pubic bone to navel. This normal and will lighten after about 3 months postpartum.

24 wks gestation  
26 wks LMP  
Length: 23 cm crown to rump (31 cm or 12 inches head to toe). Weight: about 800 gm or 1 lb 12 oz.

Fingernails are now present. 

Lungs begin to manufacture surfactant, a substance that keeps lung tissue from sticking to itself.

Baby's brain continues rapid growth. 

25 wks gestation  
27 wks LMP  
Length: 24 cm crown to rump (32.5 cm or almost 12 1/2 inches head to toe). Weight: about 910 gm.

26 wks gestation  
28 wks LMP  
Length: 25 cm crown to rump (33 cm or almost 13 inches head to toe). Weight: about 1000 gm. 

Baby's eyelids open and eyelashes are present. 

27 wks gestation  
29 wks LMP  
Length: about 26 cm crown to rump (35 cm or 13 3/4 inches head to toe). Weight: approx. 1150 gm.

Baby's lungs are developed enough to breathe air fairly efficiently but would tire rapidly. 

Toenails now visible. Baby likes to suck thumb and is developing a layer of fat under skin. 

28 wks gestation  
30 wks LMP  
Length: 27 cm crown to rump (36 cm or 14 inches head to toe). Weight: about 1300 gm or 3 lbs. 

Skin is slightly wrinkled and eyes are wide open. 

Good head of hair often present at this point. 

29 wks gestation  
31 wks LMP  
Length: 27.5 cm crown to rump (37.5 cm or about 14 3/4 inches head to toe). Weight: about 1500 gms. Beginning of third trimester!

Baby comforts by sucking thumb. Grasp is well developed and he may even grasp the umbilical cord at times. 

30 wks gestation  
32 wk LMP  
Length: 28 cm crown to rump (39 cm or 15 1/4 inche head to toe. Weight: about 1700 gms or about 3 lb 12 oz. 

Baby is able to hear sound and is getting accustomed to family voices. 

Testes descending from the abdomen, if it's a boy. Baby's brain and nerves are developing, and directing bodily functions. 

31 wks gestation  
33 wks LMP  
Length: 29 cm crown to rump (40 cm or 15 3/4 inches head to toe). Weight: about 1900 gms or 4 lbs. 5 oz. 

Baby's pupil will now constrict if light is shined in eye. 

32 wks gestation  
34 wks LMP  
Length: 30 cm crown to rump (about 41 cm or 16 inches head to toe). Weight: about 2100 gms or 4 lbs. 11 oz.

Fingernails reach the tips of the fingernails. 

Skin is pink and smooth. Baby begins to develop sleeping patterns. 

33 wks gestation  
35 wks LMP  
Length: about 31 cm crown to rump (42.5 cm or 16 1/2 inches head to toe). Weight: 2300 gms or about 5 lbs. 

Baby is putting on fat and things are getting cramped inside. Almost time to come out! 

Baby is done taking most of the iron she needs from mother. 

34 wks gestation  
36 wk LMP  
Length: 32 cm crown to rump (44 cm or 17 1/4 inches head to toe). Weight: 2500 gms or about 5 lbs. 9 oz. 

The last month of gestation begins! 

Baby gains weight most rapidly during this month: about 1/2 - 3/4 lb. per week. 

Baby settles into mom's pelvis, a process called lightening or engagement which makes mom's breathing easier; baby's new position doesn't stop her from kicking and punching. 

35 wks gestation  
37 wks LMP  
Length: 33 cm crown to rump (about 45 cm or 17 1/2 inches head to toe). Weight: 2700 gms or 6 lbs. Earliest date of full-term birth: get ready!

36 wks gestation  
38 wks LMP  
Length: 34 cm crown to rump (47.5 cm or 18 1/2 inches head to toe). Weight: 2900 gms or about 6 1/2 lbs.

Baby is fairly plump now.

Lanugo hair mostly gone except tops of shoulders and back. 

Toenails reach tips of toes; limbs are held flexed. 

37 wks gestation  
39 wks LMP  
Length: about 35 cm crown to rump (48.5 cm or 19 inches head to toe). Weight: about 3150 gms or 7 lbs. (but could be 1-3 pounds larger). 

Vernix mostly gone now. Heel creases present - a sign of fetal maturity. 

Baby may be deep in pelvis making breathing easier. Labor may have begun.

38 wks gestation  
40 wks LMP 
Length: about 20-21 inches from head to toe. Weight: about 7 1/2 lbs.

Baby may even wait up to 2 more weeks to come out.

The umbilical cord is 20-inches and will support baby through birth until the lungs take over. 

Testes are in scrotum, labia well developed. 

Fingernails extend beyond fingertips. Consider if you want to use postpartum birth control.