Fetal

Fetal refers to the fetus, the developing mammalian offspring from the ninth week of gestation until birth in humans. The term comes from Latin and is used in medicine to distinguish the later stages of prenatal development from the embryonic period. The fetal stage is characterized by growth and maturation of tissues and organs that formed during the embryonic period.

During pregnancy, the fetus relies on the placenta and umbilical cord for oxygen and nutrients and for removal of waste. Blood from the mother does not mix with fetal blood; exchange occurs across the placental barrier. Fetal circulation includes shunts such as the foramen ovale and the ductus arteriosus that redirect blood away from non-functioning fetal lungs until birth. The lungs themselves remain fluid-filled until respiration begins after birth.

Fetal development progresses through three trimesters. By the second trimester, many structures are formed and fetal movement may be felt by the mother (quickening). In the third trimester, the fetus grows rapidly and organs continue to mature in preparation for birth. Genetic, environmental, and infectious factors can influence fetal development, and prenatal care aims to monitor growth and well-being.

Common prenatal assessments include ultrasound imaging, fetal heart rate monitoring, and screening tests such as non-invasive cell-free fetal DNA analysis. Potential concerns include fetal growth restriction, neural tube defects, fetal distress, and preterm birth. The term 'fetal' is used to describe conditions, testing, or procedures related to this stage of development.