Fetal development

First Trimester

• Week 1: Conception, zygote formation, cell division begins, blastocyst implants in uterus.

• Weeks 2-3: Brain and spinal cord begin development, digestive system forms, heart starts beating, initial facial features, arms, legs, and lungs appear. Early backbone, skull, ribs, and muscle tissue visible. Embryo reaches ¼ inch.

• Month 2: Rapid head growth, brain development directs movements, liver and stomach function, limbs grow and take shape, fingers and toes develop, ears, nose, and mouth form, eyes gain color, eyelids develop. Embryo reaches 2 inches and weighs ⅓ ounce.

• Month 3: Fetus designation, bone growth, kidney function, frequent movement, toes and elbows visible, well-formed facial features, fingerprints appear, mouth opens and closes, swallowing, sex determination possible, head growth slows. Fetus reaches 4 inches and weighs 1 ounce.

Second Trimester

• Month 4: Umbilical cord and placenta fully formed, airway development (non-functional), strong heartbeat, muscle and bone development, fingernails form, sleep-wake cycles, coordinated limb movements, kicking begins. Fetus reaches 6-7 inches and weighs ½ pound.

• Month 5: Internal organ growth, increased movement felt by pregnant person, increased lung blood supply, heartbeat audible with stethoscope, eyebrow and eyelash development, scalp hair growth, regular sleep patterns, silky body hair (lanugo) and waxy coating (vernix) protect skin. Fetus reaches 9 inches and weighs 1 pound.

• Month 6: Accelerated growth, red, wrinkled, and oily skin, identifiable fingernails, stretching, kicking, and thumb-sucking, eye opening and closing, response to sound. Fetus reaches 12 inches and weighs 1 ½ pounds.

Third Trimester

• Month 7: Mature lungs capable of supporting life outside the womb, developed brain and nervous system, increasingly formed but soft bones, wrinkled skin with vernix, fatty tissue development, active kicking and stretching, visible outline of fist, foot, or head. Fetus reaches 16 inches and weighs 3 pounds.

• Month 8: Gains ½ pound per week, fully mature lungs, lanugo disappears, head-down position for birth.

• Month 9: Gains ½ pound per week, fully mature lungs, lanugo disappears, head-down position for birth. Average baby at birth is 20 inches long and weighs 7-8 pounds.

Cast of Characters

This text focuses on the development of a fetus and does not mention any specific people.

Practice Questions for Development of a Fetus

1. What is the significance of the blastocyst in early pregnancy?

   • The blastocyst is the stage where the fertilized egg implants into the uterus, starting the development of the embryo.

2. During which weeks does the brain and spinal cord begin to develop?

   • Brain and spinal cord development begins in weeks 2-3.

3. At what point in the pregnancy can sex determination be possible?

   • Sex determination is possible by the end of the third month of pregnancy.

4. What major developments occur in the fetus during month 5?

   • Internal organ growth, increased movement, and the development of eyebrows, eyelashes, and scalp hair.

5. What is lanugo, and when does it appear during fetal development?

   • Lanugo is a silky body hair that develops during month 5 to protect the skin and may disappear as birth approaches.