Pregnancy Hormones and Endocrine Changes

Pregnancy is an endocrine state organised largely around the placenta, which becomes a major hormone-producing organ. Human chorionic gonadotropin rescues the corpus luteum in early pregnancy, while progesterone, oestrogens, placental lactogen and other hormones sustain the pregnancy, remodel maternal metabolism and prepare the maternal tissues for fetal growth and, eventually, for labour.

Definition

Pregnancy hormones and endocrine changes refers to the hormones — many produced by the placenta — and the resulting endocrine adaptations that establish, maintain and ultimately end pregnancy, including the regulation of maternal metabolism and the preparation for parturition.

Scope

This topic covers the principal hormones of pregnancy and the endocrine changes they produce: human chorionic gonadotropin and the luteo-placental shift, progesterone and oestrogens, placental lactogen and growth-hormone variants, and how these hormones drive maternal metabolic adaptation and contribute to the timing of labour. It is reference physiology and does not address hormonal testing, supplementation or endocrine disorders of pregnancy.

Core questions

• What is the role of human chorionic gonadotropin in early pregnancy?
• How does hormone production shift from the corpus luteum to the placenta?
• How do progesterone and oestrogens sustain pregnancy and influence labour?
• How do placental hormones remodel maternal metabolism to support fetal growth?

Key concepts

• Human chorionic gonadotropin (hCG)
• Corpus luteum rescue and the luteo-placental shift
• Progesterone and maintenance of pregnancy
• Oestrogens in pregnancy
• Human placental lactogen
• Placentally driven maternal insulin resistance
• Functional progesterone withdrawal at labour

Mechanisms

Soon after implantation the trophoblast secretes human chorionic gonadotropin, which sustains the corpus luteum and its progesterone output until the placenta takes over steroid production — the luteo-placental shift. Progesterone maintains uterine quiescence and supports the pregnancy, while oestrogens, synthesised by the placenta from fetal and maternal precursors, promote uterine growth and blood flow and prime the myometrium. Placental lactogen and placental growth-hormone variants act on maternal metabolism, contributing to the insulin resistance and lipid mobilisation of later pregnancy that channel glucose and amino acids to the fetus. Near term, a change in the balance and action of progesterone and oestrogen — a functional progesterone withdrawal at the level of the myometrium — helps shift the uterus toward the contractile state of labour.

Clinical relevance

The endocrinology of pregnancy is the reference background for understanding why hormone levels, metabolism and uterine behaviour change across gestation. Human chorionic gonadotropin, for example, is the basis of the physiological signal that pregnancy tests detect. This entry describes normal endocrine physiology for educational orientation and is not a basis for hormonal testing, supplementation or treatment decisions.

Evidence & guidelines

The endocrine account here is synthesised from integrative reviews of placental hormone production and of placental control of maternal metabolism; this topic presents reference physiology rather than clinical recommendations.

History

The identification of human chorionic gonadotropin and the later characterisation of placental steroidogenesis, placental lactogen and the placental growth-hormone variants established the placenta as a central endocrine organ of pregnancy. Subsequent work linked these hormones to maternal metabolic adaptation and to the endocrine control of labour.

Key figures

• Laurence Cole
• Sam Mesiano

Seminal works

• costa-2016
• cole-2012
• newbern-2011

Frequently asked questions

What is human chorionic gonadotropin and why does it matter in early pregnancy?

Human chorionic gonadotropin is a hormone produced by the early placenta that sustains the corpus luteum and its progesterone output until the placenta takes over; its presence is the signal that pregnancy tests detect.

Why is the placenta described as an endocrine organ?

The placenta produces and secretes hormones such as human chorionic gonadotropin, progesterone, oestrogens and placental lactogen that maintain the pregnancy and remodel maternal metabolism, making it a major hormone-producing organ during gestation.