--- title: "Perinatal Period | Anatomy and Physiology I" description: "Perinatal period in Anatomy and Physiology I is the time around birth when a newborn shifts from placental support to breathing, feeding, and regulating itself." canonical: "https://fiveable.me/anatomy-physiology/key-terms/perinatal-period" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 28" --- # Perinatal Period | Anatomy and Physiology I ## Definition The perinatal period is the time around birth, including late pregnancy, delivery, and the first weeks after birth. In Anatomy and Physiology I, it focuses on the newborn’s rapid shift to air breathing, independent circulation, and homeostasis. ## What It Is The perinatal period is the stretch of time around birth when the fetus becomes a newborn and has to function outside the uterus. In Anatomy and Physiology I, that means looking at the immediate changes that let the baby survive after delivery, especially breathing, circulation, temperature control, and feeding. This period starts before birth because the body is already preparing for the transition. Late pregnancy matters because the lungs, circulatory system, and metabolic systems need to be ready for a sudden switch from placenta-based support to independent life. The newborn does not get oxygen through the umbilical cord anymore, so the first breaths and the first minutes after delivery are a huge physiological shift. One of the biggest changes is in the lungs. Before birth, the lungs are fluid-filled and not used for gas exchange. After birth, the baby inhales, the air sacs expand, fluid is cleared, and oxygen levels rise. That rise in oxygen helps lower pulmonary vascular resistance, which increases blood flow through the lungs so the baby can oxygenate its own blood. The circulatory system also changes fast. Fetal shunts like the foramen ovale and ductus arteriosus were useful in the womb because they routed blood away from the nonfunctioning lungs. After birth, those pathways begin to close as blood flow patterns change. This is a major example of how one organ system change triggers another. The newborn also has to manage heat, glucose, and feeding right away. Babies lose body heat quickly, so temperature regulation is a real concern. They also have to maintain blood sugar between feeds, which is why poor feeding or stress can show up as hypoglycemia. In the perinatal period, you are really watching whether the body can make the jump from fetal life to stable extrauterine life. ## Why It Matters The perinatal period is the bridge between fetal anatomy and newborn physiology, so it ties together several major course ideas at once. If you understand this window, a lot of other birth-related topics make more sense, especially respiratory transition, circulation changes, and newborn assessment. It also shows how homeostasis works under pressure. The newborn has to regulate oxygen, carbon dioxide, temperature, and blood glucose almost immediately, and any delay can affect survival. That is why perinatal complications can lead to respiratory distress, jaundice, or feeding problems that show up in the first days after birth. This term is also useful because it helps you organize what happens before, during, and after birth. You can connect prenatal development to delivery, then to the postnatal and neonatal stages. In class, that makes it easier to trace cause and effect instead of memorizing isolated facts. When you study the perinatal period, you are practicing the same kind of thinking used in health sciences: identify the normal transition, spot what can go wrong, and explain which body systems are involved. That is exactly the kind of reasoning that comes up in case questions, lab discussions, and infant assessment scenarios. ## Connections ### Prenatal Period The prenatal period comes before the perinatal period and covers development in the uterus. It matters because the fetus spends this time building the organs and systems that have to work right away after birth. If prenatal growth is incomplete or affected by poor maternal health, the transition during the perinatal period can be harder. ### Postnatal Period The postnatal period starts after birth and overlaps with the newborn’s first adjustment outside the womb. The perinatal period leads directly into it, so the same issues can continue across both time frames. In class, this helps you separate the moment of transition from the longer recovery and adaptation that follows. ### Neonatal Period The neonatal period is the early newborn stage, usually the first month after birth. It sits right after the perinatal period and is often where clinicians watch for complications that started during birth or right after delivery. If you are tracing a baby’s physiological changes, these two terms are close but not identical. ### [Apgar Score](/anatomy-physiology/key-terms/apgar-score) The Apgar score is a quick newborn assessment used during the perinatal period. It checks signs like heart rate, breathing, muscle tone, reflex response, and skin color to see how well the baby is adapting. It gives a fast snapshot of transition, not a full diagnosis. ## On the AP Exam A quiz or test question on the perinatal period usually asks you to place it in the birth timeline or explain what changes happen during this transition. You might be given a newborn case and asked why the baby is having trouble breathing, keeping warm, or maintaining blood sugar. The right answer usually connects the timing around birth to specific body systems, especially the respiratory and circulatory systems. You may also see it in an image-based question with fetal circulation, newborn monitoring, or a timeline of prenatal, perinatal, and postnatal stages. The move to make is simple: identify that this is the birth-adjacent window and then name the physiological changes happening there. If a question mentions the first few minutes or weeks after delivery, think perinatal, not just fetal development. ## Perinatal Period vs Postnatal Period These terms are close, but they are not the same. The perinatal period surrounds birth and includes the late fetal stage, delivery, and the first time after birth. The postnatal period starts after birth and focuses on the baby’s life outside the uterus. If a question is about the transition itself, use perinatal. If it is about the time after birth has already happened, use postnatal. ## Key Takeaways - The perinatal period is the time around birth, when a fetus becomes a newborn and must function without the placenta. - This period centers on rapid changes in breathing, circulation, temperature regulation, and feeding. - Fetal structures like the ductus arteriosus and foramen ovale begin to close as the baby starts using the lungs. - Problems in this window can show up as respiratory distress, hypoglycemia, jaundice, or poor adaptation to life outside the uterus. - In Anatomy and Physiology I, this term helps you connect prenatal development to postnatal newborn homeostasis. ## FAQs ### What is the perinatal period in Anatomy and Physiology I? It is the time around birth, including late pregnancy, delivery, and the first weeks after birth. In A&P, it is the period when the newborn shifts from placental dependence to independent breathing, circulation, and feeding. The big idea is transition, not just delivery itself. ### Is the perinatal period before or after birth? It includes both sides of birth. The term covers late fetal life, the actual birth process, and the early newborn stage. That is why it is different from terms that only mean before birth or only mean after birth. ### How is the perinatal period different from the neonatal period? The neonatal period is the first month after birth. The perinatal period is broader because it includes late pregnancy, labor and delivery, and the immediate time after birth. If you are studying physiological transition, perinatal is the better term. ### What body changes happen during the perinatal period? The newborn begins breathing air, pulmonary blood flow increases, fetal circulatory pathways start closing, and body temperature and glucose have to be maintained independently. These changes happen fast because the placenta is no longer doing the work. That is why this period is so closely monitored. ## Related Study Guides - [28.5 Adjustments of the Infant at Birth and Postnatal Stages ](/anatomy-physiology/unit-28/5-adjustments-infant-birth-postnatal-stages/study-guide/Go04YK5yLiBAXVS2) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/perinatal-period#resource","name":"Perinatal Period | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/perinatal-period","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/perinatal-period#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:40.569Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/perinatal-period#term","name":"Perinatal Period","description":"The perinatal period is the time around birth, including late pregnancy, delivery, and the first weeks after birth. 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