There are many hormones active in your body during pregnancy and delivery. The best known are oxytocin and prolactin, progesterone and adrenaline. We are now going to talk about a hormone Relaxin that is not so well known for most. The hormone may not be that well known, but it certainly has a positive influence on your Birth.
Relaxin is a hormone produced by the ovary and the placenta in the female reproductive system and during pregnancy. We will talk about the role during Birth.
The hormone relaxin is secreted to a higher degree during the latter part of labour. It has different effects on birthing
- Allows the uterus and vaginal walls to stretch and become evenly smooth, without narrowing bands or pushing tissues forward.
- Assists in softening the cervix and spreading the pubic region
- Causes ligaments within the baby to relax, with joints (shoulder) becoming flexible for easier descent and Birth
- weakens the amniotic membrane and allows it to release
- Loosens your ligaments, allowing the front pubic bone to shift forward to allow the baby to descend easily.
What is relaxin?
Relaxin is secreted into the circulation by the corpus luteum in the ovary. During pregnancy, it is also released from the placenta, the membranes which surround the fetus, and the lining of the uterus. The effects of relaxin are most well-described during the female reproductive cycle and pregnancy. Relaxin levels in the circulation rise after ovulation, during the second half of the menstrual cycle. At this stage it is thought to relax the wall of the uterus by inhibiting contractions, and it also prepares the lining of the uterus for pregnancy. If pregnancy does not occur, relaxin levels drop again. During pregnancy, relaxin levels are at their highest in the first trimester. At this time it is believed to promote implantation of the developing fetus into the wall of the uterus and the growth of the placenta. Early in pregnancy, relaxin also inhibits contractions in the wall of the uterus, to prevent premature childbirth. Relaxin can regulate the mother’s cardiovascular and renal systems to help them adapt to the increase in demand for oxygen and nutrients for the fetus and to process the resulting waste products. It is thought to do this by relaxing the mother’s blood vessels to increase blood flow to the placenta and kidneys.
Towards the end of pregnancy, relaxin promotes rupture of the membranes surrounding the fetus and the growth, opening and softening of the cervix and vagina to aid the process of childbirth. There is also some evidence that relaxin can relax the ligaments at the front of the pelvis to ease delivery of the baby. There are several other factors involved in labour, but the exact trigger remains unclear.
How is relaxin controlled?
The control of the release of relaxin is not yet completely clear. It is believed that the production of relaxin by the ovary during the menstrual cycle is stimulated by a pituitary hormone and that its release during pregnancy is also stimulated by the placenta. It remains unclear how it works precisely.