Pregnancy hormones and post-partum effects.

During pregnancy, women experience numerous hormonal changes that impact their daily lives. Five hormones play a particularly significant role.

• The Human Chorionic Gonadotropin hormone (hCG) : This is a glycoprotein hormone secreted exclusively by the placenta in pregnant women. In fact, this molecule is used as a marker in pregnancy tests. hCG facilitates the implantation of the egg in the uterine lining and is also responsible for the increased synthesis of oestrogen and progesterone, two steroidal hormones impacting the daily lives of pregnant women.

• The progesterone : it is produced every month by the corpus luteum, following the release of the egg into the fallopian tubes. Progesterone prepares the body for a possible pregnancy by strengthening the uterine lining (or endometrium), which aids in the implantation of the fertilised egg. When the egg is fertilised, progesterone helps to maintain the pregnancy and reduces the risk of miscarriage. It also works in synergy with oestrogens to stimulate the development of mammary glands in preparation for lactation.

• Theoestrogen : during a pregnancy, the level of oestrogen can be multiplied by 1,000. These hormones are also produced by the corpus luteum and stimulate the production of new cells in the placenta, breast, and also the uterus. This notably allows the uterus to stretch so that the baby has room to grow. Oestrogens also increase blood volume, so that the embryo can receive all the nutrients and oxygen it needs.

• Oxytocin : a significant increase in the level of this hormone is observed just before childbirth. Indeed, it is oxytocin that triggers contractions and the onset of labour. It also helps to establish the initial bond between mother and child. Oxytocin, secreted by the pituitary gland, also plays a role during breastfeeding as it promotes the ejection of milk.

• Prolactin : The secretion of prolactin increases in the days following childbirth. This hormone enables the mammary glands to secrete colostrum, a thick orange to yellow liquid, highly nutritious for the baby. The milk production then occurs approximately three days after childbirth.

Following childbirth, a significant drop in hormone levels occurs. This is particularly true for oxytocin, which has been shown to play a role in the regulation of emotions and stress. Individuals suffering from depression, for example, have a low synthesis of oxytocin. Thus, the post-childbirth period can be challenging for women. In addition to adjusting to a new routine that includes the baby, they must manage this hormonal decline, which can lead to fatigue and anxiety.

The synthesis of oestrogen also drastically decreases after childbirth. However, these hormones play a role in the serotonergic system and are capable of stimulating the production of serotonin, the so-called hormone of well-being and serenity. The drop in oestrogen levels following childbirth is another factor responsible for the baby blues experienced by some women.

Finally, the decrease in progesterone exacerbates this discomfort. Indeed, one of its intermediate components, allopregnanolone, modulates theactivity of GABA receptors at the level of brain neurons. These receptors play a major role in maintaining nervous balance and are associated with certain imbalances linked to anxiety.

• EKMEKCI T. & al. The changes in the hair cycle during gestation and the post-partum period. Journal of the European Academy of Dermatology and Venereology (2014).

• BARRERA D. & al. Steroid hormones and pregnancy. Gynecological Endocrinology (2019).