Hormones during pregnancy part 3

This series of articles continues to look at the effects of a finely tuned orchestration of hormones during pregnancy.


Mother nature in her infinite wisdom has designed a complex system of hormones to nurture and support us throughout pregnancy and childbirth. This week, I am focusing on the hormones that are involved in the finale of pregnancy and childbirth.


  • 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 twin pregnancies
  • 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

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 are there for a reason. In my final article next week we will be looking at beta-endorphins and prolactin.

Photography: Relaxin hormone – By Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute via Wikimedia Commons

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