How do your hormones affect you during pregnancy?

Pregnancy is one of the most amazing events of a woman’s life and brings with it many changes both physical and emotional.

In this article

The majority of these changes occur because of the finely tuned release of hormones essential to sustaining this new life developing and growing within our uterus (womb)

Hormones are secreted by our endocrine system, derived from the Greek ‘endo’ meaning inside and ‘crinis’ which is secrete. Their job is to trigger and regulate activity throughout our bodies. Our whole sexual health and fertility, the creation and continuation of our pregnancy depend on our hormones.

Human Chorionic Gonadotrophin (HCG)

  • Produced by the chorionic villi after implantation of an embryo
  • Stimulates an increase in production of oestrogen and progesterone in the
  • Corpus Luteum to prevent menstruation
  • Maintains high levels of hormones to maintain early pregnancy until the placenta is mature enough to take over
  • Levels peak at about 70 days
  • The main hormone measured in pregnancy tests
  • HCG may be responsible for early pregnancy symptoms such as morning sickness and fatigue


Progesterone is one of the major hormones of pregnancy and is produced initially by the corpus luteum, followed by the placenta with a steady rise in levels until labour and birth when there is a rapid drop in levels. This drop may also be one of the triggers to facilitate the onset of labour.

  • During implantation and early gestation, progesterone appears to decrease your maternal immune response to allow for the acceptance of pregnancy by your body
  • It decreases contractility of the uterine smooth muscle by preventing contractions, and helping to maintain your pregnancy
  • It is a major hormone of pregnancy
  • Produced initially by the Corpus Luteum of the ovary
  • Progesterone is produced by the placenta from approximately 12 weeks of pregnancy with a steady rise in levels until labour and birth
  • Levels of progesterone drop at the end of pregnancy which may be a ‘trigger’ for the onset of labour


  • The main source of oestrogens in pregnancy is the placenta but they are also produced by the maternal and fetal adrenal glands
  • The production of oestrogen is complex and requires a close interaction between both placenta and fetus for synthesis to occur
  • Oestrogen regulates progesterone, protecting your pregnancy
  • Maintains both uterine blood flow and the endometrium (lining of your uterus) during your pregnancy
  • Increases blood flow to mucous membranes, hence the congestion of sinuses and a stuffy nose!
  • Encourages the growth of milk ducts within the breast, and enhances the effects of prolactin which stimulates milk production
  • Oestrogen is responsible for the growth and maturation of fetal organs such as the lungs, kidneys, and liver, as well as reproductive organs
  • It also regulates bone density as your baby develops and grows
  • Finally, oestrogen protects female babies in-utero from the effects of male hormones

Human Chorionic Somatomammotrophin (HCS)

  • Commonly called Human Placental Lactogen (HPL) is produced by the syncytiotrophoblast
  • The secretion of HPL is complementary to that of HCG, and as the level of the latter falls as HPL increases
  • It appears to alter your metabolism so that your baby thrives and grows, as you use more fatty acids leaving more glucose for your baby to thrive
  • In conjunction with oestrogen and cortisol, HPL can block the action of insulin from approximately 20-24 weeks of pregnancy elevating blood sugar levels, which may be a precursor for gestational diabetes
  • This hormone helper initiates changes in preparation for breastfeeding activating the secretion of colostrum

Melanocyte Stimulating Hormone

  • A combination of oestrogen, progesterone and melanocyte stimulating hormone can cause skin discolouration (skin pigmentation) affecting your nipples, areola and linea nigra (the line that runs down from your abdomen to your pubic bone).
  • Causes the tanned look of the skin on your face commonly known as ‘chloasma’ or mask of pregnancy
  • May increase your susceptibility to sunlight, so take extra care when out and about in the sun

Mother nature in her infinite wisdom has designed a complex system of hormones to nurture and support us throughout pregnancy leading to the ultimate climax of childbirth. The hormones that are involved in this finale of pregnancy and childbirth are:


  • Belonging to the insulin family relaxin is a protein hormone produced by the corpus luteum, breasts and placenta
  • During pregnancy relaxin is found in ten times its normal concentration
  • It relaxes smooth muscle, joints and ligaments, and promotes dilation of blood vessels in organs and tissues including the uterus, mammary glands and heart
  • Reaches peak levels at 14 weeks and again at delivery
  • Contributes to symptoms of heartburn, and pelvic girdle discomfort
  • Relaxin helps increase the space for baby to pass through the birth canal
  • It also softens and lengthens the cervix
  • High levels are found in women with type 1 diabetes as well as twins pregnancy
  • Effects can last up to 5 months post delivery


  • Oxytocin is commonly known as the ‘love’ hormone as it is released in pulses during lovemaking, childbirth and breastfeeding, and engenders emotions of love
  • Produced by the Hypothalamus and stored in the posterior Pituitary gland
  • Outside the brain oxytocin-containing cells have been identified in diverse places including the placenta, thymus, adrenal medulla, pancreas and retina
  • Oxytocin causes the rhythmic uterine contractions of labour, and levels soar towards the end of labour stimulated by ‘stretch receptors’ in the vagina as baby descends
  • It is also responsible for the ‘fetal ejection reflex’ at the end of childbirth facilitating birthing quickly and easily at the end of an undisturbed labour
  • These high levels also benefit your baby as they cross the placental barrier and switch off baby’s brain cells reducing the amount of oxygen required during labour
  • Following delivery oxytocin stimulates the ‘placental ejection reflex reducing the risk of haemorrhage and also triggers the ‘milk ejection’ or ‘let down’ reflex in breastfeeding
  • Your baby has also been producing oxytocin so that crucial bonding is initiated between you both, enhanced by skin to skin touching
  • Suckling at the breast stimulates more oxytocin to be produced via the hypothalamus
  • Oxytocin promotes feeling of contentment, a reduction in anxiety and feelings of calmness
  • High levels of ‘stress hormones’ interfere with oxytocin levels during labour and may cause a delay in progress
  • Synthetic oxytocin does not cross the blood/brain barrier except in small amounts therefore, does not have the same euphoric effects as natural oxytocin

Childbirth involves peak levels of oxytocin and prolactin. Add to these beta-endorphins our body’s natural analgesia, and our ‘fight or flight’ hormones adrenaline and noradrenaline, (which may aid the fetal ejection reflex just before birth) and we have a potent cocktail to aid us in birthing and early parenting.


  • Beta-endorphins are stress hormones produced in the pituitary gland and inhibits the perception of pain
  • High levels are present during lovemaking, pregnancy, birth and breastfeeding
  • A naturally occurring opiate with analgesic properties similar to synthetic opiates such as pethidine.
  • Suppresses the immune system which may be an important factor during early pregnancy aiding acceptance by our body of our developing baby
  • It induces feelings of pleasure, euphoria and dependency
  • Very high levels during labour, help women to transcend pain and reach an altered state of awareness or ‘zone out’

Fight or Flight Response Hormones

  • Hormones adrenaline and noradrenaline comprise our fight or flight response to stress or danger
  • Collectively they are known as catecholamines (CA)
  • They are secreted by the adrenal glands in response to stressors, whereby they activate the sympathetic nervous system for fight or flight
  • In the first stage of labour high levels of catecholamines inhibit oxytocin production which in turn slows or stalls labour
  • They also reduce blood flow to the uterus, placenta and indirectly to the baby as the blood is redirected to major muscles groups
  • Therefore, high levels of these hormones may prolong labour and lead to fetal distress
  • Recent research has indicated that a sudden increase in catecholamines at the end of labour may be beneficial, activating the ‘fetal ejection reflex’ and a surge of strong contractions facilitating an easy and quick birth
  • Post delivery effects include a rapid drop in levels and subsequent side effects of feeling cold and shivery, when it is important to remain warm
  • Baby also experiences high catecholamine levels at birth, which ensures that he/she is alert and responsive, important for bonding and breastfeeding


  • Commonly known as the ‘mothering’ hormone prolactin is produced in the pituitry gland
  • Increased levels during pregnancy promote development and enlargement of the mammary glands of the breasts
  • Falling levels of progesterone stimulate milk production in conjunction with your baby’s sucking stimulation
  • Contributes to the surfactant synthesis of your baby’s lungs which help them to mature
  • Prolactin may make you feel more maternal
  • High levels are found in fathers to be closely involved with their baby promoting bonding and reducing testosterone levels and libido, but not sexual function!
  • Prolactin is produced during sleep and levels are highest at night, hence the importance of night breastfeeding for lactation
  • Babies also produces prolactin in pregnancy and early research indicates it may play a role in maturation of a baby’s brain/hormone system

Each hormone has its own unique and vital part to play in our ability to procreate, nurture, support and protect our babies during pregnancy and childbirth. Each one is vital, and although the side effects are not always pleasant, it is reassuring to know they won’t last forever and the reward is a beautiful baby at the end of the day!

If you would like any further advice on pregnancy or birth you can contact Amanda on: 0905 620 1241 (£1.02/minute from a BT landline. Calls from other networks and mobiles may vary*) or view my profile..

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Written by

Amanda Gwynne
Midwife, HypnoBirthing & Fertility

Amanda has combined her expertise in midwifery over 30 years with skills in complementary therapies and HypnoBirthing, offering a holistic approach to fertility, pregnancy, birth and beyond. She lectures to health professionals and contributes regularly to parenting magazines