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10th December 2018

The Six Key Pregnancy Hormones

In this article, Consultant Gynaecologist Pradnya Pisal provides information on each of the six key pregnancy hormones. These hormones contribute to the emotional and physiological changes women tend to experience when pregnant.


  • Pregnancy stage: HCG appears on the 8th day after ovulation, one of the earliest secreted hormones from the conceptus, and can be detected usually by 5-6 days after ovulation but definitely by 10 days after ovulation.
  • Peak time: it generally doubles every 48 hours, reaching its maximum level at 8-10 weeks.
  • Function: its only function is supporting the corpus luteum. 
  • Side effects: headache, irritability, restlessness, fatigue, insomnia, nausea, vomiting (can be excessive and abnormal) and fluid retention. 


  • Pregnancy stage: oestrogen is produced from pre-pregnancy until about 10-12 weeks from the follicle area in the ovary, where the egg is released from. After this, the placenta and fetal adrenal gland produce it until term.
  • Peak time: late third trimester.
  • Function: preparing uterine lining for the implantation of the embryo. It is helpful in preventing miscarriage, and acts as a catalyst for chemical changes for growth, development and energy in the baby. It steps up blood circulation and regulates the production of other key hormones, as well as promoting breast engorgement in early pregnancy and regulating bone density. 
  • Side effects: increased blood flow to mucous membranes leading to headache, postnasal drip and nasal congestion; sensitive skin and some areas showing hyper-pigmentation (especially nipple areola and along midline on abdominal wall); melasma.


  • Pregnancy stage: progesterone is produced from pre-pregnancy until about 10-12 weeks from the follicle area in the ovary where the egg is released from. The placenta then produces it until term. There is a second gradual increase after 32 weeks.
  • Peak time: late third trimester
  • Function: preparing uterine lining for the implantation of the embryo, suppressing maternal response to fatal antigens and prevents the rejection of trophoblast. It maintains quiescence of the uterine muscle and is helpful in preventing miscarriage and pre-term labour. It also encourages breast tissue growth.
  • Side effects: GI discomfort, including indigestion, heartburn, constipation and bloating.  Aching hips (pubic bone and back), bleeding from teeth and gums and increased sweat gland secretion. 


  • Pregnancy stage: produced by the corpus luteum and the placenta from early pregnancy to late pregnancy.
  • Peak time: at 14 weeks and around the time of delivery.
  • Function: preparing uterine lining for the implantation of the embryo, uterine growth and accommodation, the control of myometrial activity to prevent preterm labour, and cervical ripening and the facilitation of labour. It is also important in reducing insulin resistance.
  • Side effects: joint and ligament pains and backache. It can also cause heartburn as it relaxes the smooth muscle and sphincter of the stomach, so acid comes up into the food pipe.


  • Pregnancy stage: produced by the hypothalamus and released from the pituitary gland in the mother’s brain throughout pregnancy.
  • Peak time: oxytocin levels rise from the first to the third trimester and fall during the postpartum period.
  • Function: stimulates the ripening of the cervix, leading to successive dilation during labour. Along with other hormones, it causes the release of prostaglandins, which play an important role in the ripening of the cervix. It also aids bonding with the baby. 
  • Side effects: can cause irritability and awareness of normal uterine contractions, Braxton-Hicks.  Can lead to excessive hair growth. 


  • Pregnancy stage: secreted by the decidua, endometrial lining and also by maternal pituitary gland, starting in early pregnancy. 
  • Peak time: starts in early pregnancy and there is a sustained rise until the third trimester and postnatally.
  • Function: enlargement of the mammary glands and preparation for milk production, which normally starts when levels of progesterone fall by the end of pregnancy and a suckling stimulus is present.
  • Side effects: n/a


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