In addition to the well-known estrogen, progesterone and human chorionogonadotropin (hCG), other hormones are involved in maintaining your pregnancy and preparing your body for childbirth. These hormones include oxytocin, prolactin, and relaxin, hormones that have both pregnancy-related and non-pregnancy related functions in your body.
Oxytocin – the hormone of love and bonding
As well as playing a role in social bonding and sexual reproduction, oxytocin has important functions during pregnancy, childbirth, and in the first year or so after delivery. Oxytocin is present throughout your pregnancy and levels of oxytocin during the first trimester of pregnancy have been found to predict bonding behavior of mothers with the their babies after birth. In the initial stages of labor, the contractions of your uterus are caused by rising levels of oxytocin. In the second and final stage of labor, oxytocin, along with another biochemical called noradrenaline, triggers the so-colled ‘fetal ejection reflex’, which is the final series of muscular contractions that push the baby out.
In the third stage of labor, after the baby is born, oxytocin’s function is to keep the uterus contracting so as to push the placenta out of the uterus, close off the blood vessels that were attached to it, and begin to shrink the uterus back to its normal size.
High levels of oxytocin in both mother and baby promote mutual attachment, and oxytocin, along with beta-endorphin, results in the ‘let-down reflex’, which helps to enable the breasts to start producing milk.
Relaxin – Time to start loosening up!
Relaxin is present in your body when you are not pregnant, but at much lower levels. Once you are pregnant, levels of relaxin rise and reach a peak during the first trimester. During this time, relaxin helps with implantation and the growth of the placenta and helps to prevent preterm birth through inhibiting contractions of the uterus. Relaxin also regulates your cardiovascular and renal systems to help them adapt to the extra workload that occurs during pregnancy. Towards the end of pregnancy, relaxin promotes rupture of the membranes surrounding the fetus and helps to prepare your body for delivery of your baby through the birth canal by softening of the cervix and vagina, loosening up the ligaments that hold your pelvic bones together, and relaxing the uterine muscle. An unwanted effect of relaxin is the loosening of non-pregnancy related ligaments, such as your knees, hips, and ankles. This can lead to pain and inflammation and even result in your feet becoming permanently bigger!
Prolactin – the milk production hormone
The main function of prolactin, the levels of which increase 10–20 times during pregnancy, is to promote milk production. It does this through preparing the breast tissues for lactation. After the birth of your baby, prolactin levels increase and this initial increase is what gets milk production started. But to maintain prolactin levels, and therefore the production of breast milk, you need to either breastfeed or pump. Either of these actions will stimulate the release of prolactin and this then stimulates the milk glands to make more milk.