Fetal Development

DAY 1: Fertilization4-5 wk

The sperm joins with the ovum to form one cell. This one cell contains the complex genetic makeup for every detail of a new human being—the child’s sex, hair and eye color, height, skin tone, etc. From that moment on nothing new is added but oxygen, nutrition, and time.1

1st Month (1-4 Weeks)

The first cell divides in two, and cell division continues as the newly formed individual travels down the fallopian tube to the uterus. Over 500 cells are present when this tiny embryo (the blastocyst*) reaches the uterus 7 to 10 days after fertilization.2

Foundations of the brain, spinal cord, and nervous system are already established, and by day 21 the heart begins to beat in a regular fashion with a blood type often different from the mother.3 Muscles are forming, and arms, legs, eyes, and ears have begun to show. *The blastocyst is the stage at which many researchers want to destroy the embryo in order to harvest stem cells.

6 week2nd Month (5-8 Weeks)

By 6 weeks, brain waves can be detected by electroencephalogram and the brain is controlling 40 sets of muscles as well as the organs.4 The jaw forms, including teeth and taste buds.5 The baby begins to swallow amniotic fluid, and some have been observed hiccupping.6 During this time, the stomach produces digestive juices, and the kidneys begin to function.7 Fingers and toes are developing, and at 7 weeks the chest and abdomen are fully formed.8 swimmer’s stroke looks like a miniature human infant.9,10

3rd Month (9-12 Weeks)

Unique fingerprints are evident and never change.11 The baby now sleeps, awakens, and exercises her muscles by turning her head, curling her toes, and opening and closing her mouth. Even though mom cannot feel movement yet, the baby is very active. She breathes amniotic fluid to help develop her respiratory system. The sex can be visually determined, and family resemblances may appear as well!12 By the end of the month all the organs and systems of her body are functioning.13 This is the stage when most abortions occur.

4th Month (13-16 Weeks)

By the end of this month, the baby is 8-10 inches in length and weighs about ½ pound. Her ears are functioning and she hears her mother’s heartbeat, as well as external noises like music. Mom begins to feel the baby’s movement—a slight flutter at first that will become stronger.14 Lifesaving surgery has been performed on babies at this age.

5th Month(17-20 Weeks)

If a sound is especially loud, the baby may jump in reaction to it. Thumbsucking has been observed during the fifth month.15

6th Month (21-24Weeks)20 week

Oil and sweat glands are functioning. The baby’s delicate skin is protected in the amniotic sac by a special ointment called vernix. She grows rapidly in size and strength while her lungs become more developed.16 In a recent study, 70% of babies born between 22 and 26 weeks lived past age one thanks to modern medicine.17

7th Month (25-28 Weeks)

The baby can now recognize her mother’s voice. She exercises by stretching and kicking as she grows even bigger. She uses the senses of hearing, touch, and taste, and she can even look around with open eyes at her watery home.18 If the baby is a boy, his testicles descend from the abdomen into the scrotum.19

8th Month (29-32Weeks)

The skin begins to thicken, with a layer of fat stored underneath for insulation and nourishment. The baby swallows a gallon of amniotic fluid per day and often hiccups.20 Though movement is limited due to cramped quarters, the baby’s kicks are stronger, and mom may be able to feel an elbow or heel against her abdomen.21

9th Month (33-36 Weeks)

Gaining a half pound per week, the baby is getting ready for birth. The bones in her head are soft and flexible to more easily mold for the journey down the birth canal.22 Of the 45 generations of cell divisions before adulthood, 41 have already taken place. Only four more come before adolescence. Ninety percent of a person’s development happens in the womb.23

1 American Baby. 1989.„ 2 Mayo Clinic Family Health Book. 2003.„ 3 Moore and Persaud. The Developing Human.„  4 JAMA. 1964.„ 5 Langman’s MedicalEmbryology. 1995.„ 6 Early HumanDevelopment. 1985.„ 7 The Gale Encyclopedia of Medicine. 2nd ed. „ 8 Mayo Clinic Family Health Book.2003.„ 9 Valman & Pearson. British Medical Journal.„ 10 Mayo Clinic Family Health Book. 2003.„ 11 Moore and Persaud. The Developing Human.„ 12 Flanagan. Beginning Life. „ 13 Cunningham, MacDonald et al. Obstetrics.„ 14 Flanagan. Beginning Life.„ 15 Clinical Reference Systems Annual 2001.„ 16 The Gale Encyclopedia of Medicine. 2nd ed.„ 17 JAMA. 2009.„ 18 Ibid.„ 19 Clinical Reference Systems Annual 2001.„ 20 Ibid.„ 21 Ibid.„ 22 Ibid.„ 23 Sassone, Robert L. “Interview with Prof. Sir A. William Liley.” The Tiniest Humans.„ 
*For full citations visit www.human life.org/did_you_know.php.
Reprinted with permission from Human Life Alliance www.humanlife.org