Pregnancy: Hormonal and Endocrine Changes

The endocrine environment of pregnancy is transformed by hormones produced by the placenta and by adapted maternal endocrine glands. Human chorionic gonadotropin, progesterone, oestrogens, and human placental lactogen, together with changes in thyroid, adrenal, and pituitary function, coordinate much of the systemic maternal adaptation and underlie many common features of pregnancy.

Definition

The hormonal and endocrine changes of pregnancy are the shifts in production and action of reproductive and metabolic hormones, dominated by placental output of human chorionic gonadotropin, progesterone, oestrogens, and human placental lactogen, alongside adapted maternal thyroid, adrenal, and pituitary function, that sustain the pregnancy and drive maternal physiological adaptation.

Scope

This topic covers the principal hormones of pregnancy, the placenta's role as an endocrine organ, and the broad direction of changes in maternal thyroid, adrenal, and pituitary activity. It explains how these endocrine signals drive adaptations elsewhere in the body. It is a reference overview and does not address the management of endocrine disorders in pregnancy.

Core questions

• Which hormones are produced by the placenta, and what are their broad roles?
• How does the corpus luteum-to-placenta transition maintain early pregnancy?
• How do maternal thyroid, adrenal, and pituitary function adapt during pregnancy?
• How do these endocrine signals translate into systemic maternal change?

Key concepts

• Human chorionic gonadotropin (hCG)
• Progesterone
• Oestrogens
• Human placental lactogen (hPL)
• Placenta as an endocrine organ
• Corpus luteum rescue and luteo-placental shift
• Gestational thyroid and adrenal adaptation

Mechanisms

After implantation, trophoblast-derived human chorionic gonadotropin sustains the corpus luteum and its progesterone output until the placenta takes over steroid production. The placenta then secretes large amounts of progesterone and oestrogens, which act on the uterus, breasts, cardiovascular system, and smooth muscle, while human placental lactogen contributes to the maternal shift toward insulin resistance that prioritises fetal fuel supply. Maternal thyroid activity rises, partly because human chorionic gonadotropin has weak thyroid-stimulating activity and because oestrogen increases thyroxine-binding globulin, and adrenal cortisol output increases over gestation. These coordinated endocrine signals account for much of the cardiovascular, metabolic, and gastrointestinal adaptation described in the sibling topics.

Clinical relevance

Because hormones such as human chorionic gonadotropin underpin pregnancy testing and because endocrine adaptation shifts thyroid and other reference ranges, understanding these changes is part of interpreting maternal investigations correctly. This entry is educational background on normal endocrine physiology and is not guidance for diagnosing or managing endocrine conditions in any individual.

Evidence & guidelines

The endocrine physiology summarised here is drawn from review syntheses such as Torricelli and Petraglia (2010) on placental hormones and broader physiology reviews including Soma-Pillay and colleagues (2016) and Costantine (2014). These are narrative reviews of established endocrinology rather than graded recommendations.

Seminal works

• torricelli-2010
• soma-pillay-2016

Frequently asked questions

What does human chorionic gonadotropin do in early pregnancy?

It is produced by the trophoblast and maintains the corpus luteum so that progesterone continues to support the early pregnancy until the placenta takes over hormone production; it is also the hormone detected by pregnancy tests.

Why does thyroid function change in pregnancy?

Oestrogen raises thyroxine-binding globulin and human chorionic gonadotropin has mild thyroid-stimulating activity, so thyroid hormone production and reference ranges shift compared with the non-pregnant state.