Fetal Development and Related Nursing Care

Fetal development refers to the formation and growth of an infant that occurs over 39 to 40 weeks to prepare for extrauterine life. Fetal development can be divided into three main stages: zygote, embryonic, and fetal.

The first stage, called the zygote stage, begins with conception, when a sperm fertilizes an egg forming a zygote. As the zygote undergoes cell division and develops, it travels through the fallopian tube until it implants in the inner lining of the uterus, or endometrium. This entire process takes about two weeks. Next is the second stage, called the embryonic stage, which takes place from weeks 3 through 8 of gestation. This is when the embryo begins to develop three primary germ layers called the ectoderm, mesoderm, and endoderm, which will eventually give rise to all the organs and tissues of the embryo. For instance, the ectoderm develops into the nervous system along with skin, and the bones that form the skull; the mesoderm develops into structures like skeletal muscles, bone, and the circulatory system; and the endoderm develops into the pulmonary, gastrointestinal, and endocrine systems. Since all major organ systems form during this time, the embryo is especially vulnerable to teratogens, or substances that can damage cells and cause abnormalities in development. Finally, the third stage, called the fetal stage, takes place from the ninth week until birth and is characterized by rapid growth and development. During weeks 9 through 12, the central nervous system, GI system, and heart are fully developed. This is also when the heartbeat can be detected via doppler ultrasound, and spontaneous fetal movements occur. Other developmental milestones include differentiation of genitals as male or female; production and secretion of urine by the kidneys; and production of blood cells within the liver, spleen, and lymphatic tissue.

Between weeks 13 and 16, lanugo, or soft, fine hairs, cover the fetal body, The fetus also begins to swallow amniotic fluid and produce meconium, which is the first stool of a newborn. During weeks 17 through 20, sebaceous glands begin secreting vernix caseosa, which is a white, creamy, cheese-like substance that protects the skin; and brown fat deposits around the kidneys and behind the sternum and neck. Also, genitalia become visible on ultrasound, and fetal movements can be felt by the mother as fluttering sensations, known as quickening.

Between weeks 21 and 24, the lungs begin producing small amounts of surfactant which helps prevent the collapse of alveoli. By week 25 the fetus is considered viable, meaning survival outside the uterus is possible.

During weeks 25 through 28, the eyelids open, lanugo starts to disappear, and bone marrow takes over red blood cell production from the spleen. From weeks 29 to 32, surfactant production reaches mature levels in the lungs, and the skin becomes pigmented. Between weeks 33 and 38, the lungs become capable of gas exchange, most lanugo disappears, and subcutaneous adipose tissue increases. At 39 to 40 weeks, the fetus is considered full term.

Placenta Now, fetal development is supported by the placenta, which is a temporary organ responsible for fetal respiration, nutrition, and excretion. It also secretes hormones essential for sustaining pregnancy, including progesterone, estrogen, human chorionic gonadotropin, and human placental lactogen. A thin membrane, known as the placental membrane, keeps the maternal and fetal blood from mixing; however, most substances, like medications, nicotine, and caffeine, can be transferred across the placental membrane.