Pregnancy Physiology
Pregnancy physiology is the study of the integrated, reversible changes that occur in the maternal body and in the developing conceptus across gestation. From conception to birth the mother's cardiovascular, respiratory, renal, metabolic, haematological and endocrine systems remodel to support the growth of the fetus, while the placenta acts as the interface for gas, nutrient and hormone exchange between the two circulations.
Definition
Pregnancy physiology is the branch of reproductive physiology concerned with the normal functional adaptations of the maternal organism and the developmental physiology of the conceptus, mediated by the placenta, from implantation through to delivery and the immediate postpartum return toward the non-pregnant state.
Scope
This area orients the reader to the major physiological themes of human pregnancy and links to the detailed topics beneath it: maternal cardiovascular adaptation, respiratory and metabolic adaptation, fetal development and physiology, parturition and labour, and the endocrine changes of pregnancy. It treats these as reference physiology, not as antenatal or obstetric management guidance.
Sub-topics
Core questions
- How do maternal organ systems remodel to meet the demands of the growing fetus?
- How does the placenta mediate exchange and hormone production between mother and fetus?
- How does the fetus develop functioning organ systems in utero and prepare for the transition to extrauterine life?
- What signals coordinate the timing and progression of parturition?
Key concepts
- Maternal adaptation to gestation
- Maternal-fetal exchange across the placenta
- Plasma volume expansion and physiological haemodilution
- Insulin resistance of pregnancy
- Fetoplacental unit
- Transition to extrauterine life
- Onset and progression of labour
Mechanisms
Pregnancy reorganises maternal physiology around the needs of the fetoplacental unit. Plasma volume and cardiac output rise while systemic vascular resistance falls, ventilation increases, renal plasma flow and glomerular filtration climb, and metabolism shifts toward an insulin-resistant, lipid-mobilising state in late gestation to prioritise fetal substrate supply. These changes are driven largely by placental and ovarian hormones. The placenta itself provides the exchange surface across which oxygen, carbon dioxide, nutrients and waste pass between separated maternal and fetal circulations, and it secretes the hormones that sustain the pregnancy. At term, a coordinated endocrine and mechanical cascade converts the quiescent uterus into a contractile organ, producing labour and delivery.
Clinical relevance
Understanding normal pregnancy physiology is the reference background against which deviations of pregnancy are recognised and interpreted in the health sciences. It explains why laboratory and haemodynamic reference ranges differ in pregnancy and why the pregnant body responds differently to physiological stress. This entry describes normal function for educational orientation and is not a source of antenatal, diagnostic or treatment guidance.
Evidence & guidelines
The physiological picture summarised here is drawn from integrative narrative reviews of maternal adaptation and placental function; detailed, citation-level evidence is presented in the topic entries beneath this area.
History
Systematic description of maternal adaptation to pregnancy accumulated through twentieth-century physiology and obstetric medicine, with serial measurements of cardiac output, blood volume, ventilation and renal function establishing the now-classic trajectories. Parallel work on the placenta and on the endocrinology of gestation clarified how the fetoplacental unit sustains and ultimately ends the pregnancy.
Related topics
Seminal works
- soma-pillay-2016
- sanghavi-2014
- smith-2007
Frequently asked questions
- What does pregnancy physiology cover?
- It covers the normal, reversible adaptations of the mother's organ systems during gestation and the developmental physiology of the fetus and placenta, from implantation through delivery.
- Why do normal laboratory values change in pregnancy?
- Plasma volume expansion, increased cardiac output and renal blood flow, ventilatory changes and altered metabolism shift many haematological, biochemical and haemodynamic reference values away from the non-pregnant range, which is a normal feature of adaptation rather than disease.