Timeline of human prenatal development

Timeline of human prenatal development

The timeline of human prenatal development outlines the key stages and milestones in the development of a human embryo and fetus from conception to birth. This process is divided into three main stages: the germinal stage, the embryonic stage, and the fetal stage. Each stage is characterized by specific developmental events and changes.

Germinal Stage

The germinal stage begins at fertilization and lasts until the end of the second week. During this period, the zygote undergoes rapid cell division and forms a blastocyst, which implants into the uterine wall.

Fertilization

Fertilization occurs when a sperm cell penetrates an ovum, resulting in the formation of a zygote. This marks the beginning of a new human life.

Implantation

Around 6 to 10 days after fertilization, the blastocyst implants into the uterine wall, establishing the foundation for the placenta and the developing embryo.

Embryonic Stage

The embryonic stage spans from the third to the eighth week of development. During this time, the embryo undergoes significant growth and differentiation, forming the basic structures of the body.

6 weeks pregnant

Week 3

The gastrulation process begins, leading to the formation of the three primary germ layers: the ectoderm, mesoderm, and endoderm. These layers give rise to all tissues and organs.

Week 4

The neural tube, which will become the central nervous system, starts to form. The heart begins to beat, and the basic structure of the face and limbs starts to develop.

Week 5

The embryo is now about 1.5 mm long. The brain continues to develop rapidly, and the eyes and ears begin to form.

Week 6

The embryo's heart is now beating at a regular rhythm. The limb buds become more pronounced, and the digestive system starts to develop.

Tubal pregnancy with embryo

Week 7

The embryo is approximately 10 mm in length. The lungs begin to form, and the intestines start to develop outside the body in the umbilical cord.

Week 8

The embryo is now referred to as a fetus. All major organs have begun to form, and the skeleton starts to ossify.

Fetal Stage

The fetal stage extends from the ninth week until birth. During this period, the fetus grows in size and weight, and the organs continue to mature.

Human embryo

Week 9

The fetus is about 2.5 cm long. The head is large compared to the rest of the body, and the face is more developed.

9-week human embryo from ectopic pregnancy

Week 10

The fetus is approximately 3.5 cm long. The fingers and toes are distinct, and the nervous system is responsive.

10 weeks pregnant

Week 11

The fetus is about 5 cm long. The genitals begin to form, and the liver starts to produce red blood cells.

Week 12

The fetus is approximately 6 cm long. The placenta is fully functional, and the kidneys begin to produce urine.

Human fetus 10 weeks with amniotic sac

Related Pages

• Pregnancy
• Embryogenesis
• Fetal development
• Human reproduction