At 28 weeks of fetal development, what critical substance is formed for the baby to breathe at birth?

At 28 weeks of fetal development, the formation of surfactant is indeed a critical milestone for the fetus's ability to breathe after birth. Surfactant is a lipoprotein complex that reduces surface tension within the alveoli of the lungs, preventing collapse and allowing for proper expansion during breathing. The production of surfactant typically begins around 24 to 28 weeks of gestation, and its levels increase significantly as the pregnancy progresses, peaking just before delivery. This substance is essential for normal respiratory function at birth, especially for preterm infants, who may struggle with respiratory distress syndrome if they have insufficient surfactant.

Amniotic fluid surrounds and protects the fetus but does not directly aid in breathing after birth. Vernix is a protective coating on the skin of the fetus that helps prevent skin maceration in the amniotic fluid but does not play a role in respiratory function. Lanugo consists of fine hair that covers the fetus and also does not contribute to the ability to breathe post-delivery. Thus, surfactant’s role in enabling the lungs to function effectively upon birth makes it the correct focus in this question.