They are accused of many ailments during pregnancy, but beyond the small inconvenience they cause, hormones are essential for the proper development of pregnancy and childbirth. HCG, progesterone, oxytocin,…: review of these different pregnancy hormones and their role.

Secretion mechanisms

After ovulation, the walls of the ruptured follicle collapse and blood capillaries develop there. The follicle then turns into a gland, the corpus luteum, which will secrete various hormones essential for the proper development of pregnancy.

If there has been fertilization, the egg implants itself in the uterine lining. This stage, called implantation, takes place about 7 days after fertilization. The egg’s outer cell layer then begins to secrete chorionic gonadotropin hormone (HCG). The level of HCG increases very quickly up to 8-10 weeks of pregnancy; it doubles on average every 31 hours to reach a peak around the 10th week. In the 3rd month, the secretion of HCG decreases very markedly and the placenta takes over.

His role

The high level of HCG allows to keep the corpus luteum in activity for 3 months and through this, to ensure the secretion of two hormones essential for pregnancy: estrogen and progesterone. HCG is therefore a key hormone in early pregnancy.

The increase in the level of HCG is incriminated in various ailments of the beginning of pregnancy, starting with the nausea often present in the first trimester of pregnancy and which generally subsides in the 3rd month, at the same time as the decrease in the level of HCG.

The analysis of the level of HCG

The detection of HCG in the urine (for urine tests available in pharmacies) or in the blood (for pregnancy tests prescribed by the doctor and performed in the laboratory) can confirm the presence of a pregnancy.

The serum HCG level also makes it possible to monitor the progress of the pregnancy and to diagnose a non-progressive pregnancy (molar pregnancy, ectopic pregnancy).

Secretion mechanisms

The role of progesterone is to prepare the uterine lining for implantation. If there is no fertilization, the corpus luteum regresses and stops secreting progesterone. This sudden fall leads to the desquamation of the uterine lining, namely the rules.

In pregnancy, the corpus luteum secretes progesterone in quantity up to the 9-10th week. In the 4th month, the placenta takes over. Placental progesterone is metabolized 3/4 in the maternal body, the remaining 1/4 by the fetus.

His role

By causing all the smooth muscles to relax, progesterone helps keep the baby in the uterine muscle throughout pregnancy. It also has a relaxing effect on the venous walls, which allows the body to adapt to physiological hypervolemia (increase in blood volume) during pregnancy. This relaxant effect causes various minor ailments: constipation due to lazy transit, acid reflux due to slower gastric emptying, drop in blood pressure, poor venous return, etc.

Progesterone is also involved in preparing the breasts for breastfeeding by promoting the increase in the mammary glands. Along with estrogen, it inhibits lactation during pregnancy by blocking the action of prolactin on the mammary gland. Some of the progesterone is also used by the baby to make other hormones such as adrenaline and testosterone.

At the end of pregnancy, under the effect of a hormone secreted by the baby’s pituitary gland, the progesterone level drops sharply. The relaxant effect disappears and the muscle fibers of the uterus will then be able to contract during the contractions.

Analysis of progesterone levels

The blood level of progesterone makes it possible to ensure the good evolution of the beginning of pregnancy. Combined with the level of HCG, it is used in the diagnosis of ectopic pregnancy. The progesterone level will then be abnormally low.

Secretion mechanisms

In early pregnancy, estrogen is secreted by the corpus luteum. After the 8th week, the placenta becomes the major source of maternal estrogen, especially estriol. the baby also plays a role in the secretion of estrogen: the adrenal glands of the fetus produce an andogenic hormone which, while circulating through the placenta, is changed into estrogen.

His role

Estrogens also have a relaxing effect on the various tissues of the body and promote the growth of the uterus. They increase cardiac frequency and output as well as circulatory output and contractility of the myocardium. Like progesterone, they help prepare the breasts for breastfeeding. Estriol causes the synthesis of prolactin, the galactogenic hormone.

Estrogens could have their share of responsibility in the onset of nausea in pregnancy by causing hypersensitivity of smell. But they also have good sides: a radiant complexion, well hydrated skin, silky hair.

The placental galactogenic hormone (HPL) is secreted by the syncytiotrophoblast (one of the tissues of the trophoblast, the future placenta). It is detectable in maternal blood from the 3rd week of pregnancy. One of its roles is to provide the fetus with sufficient and constant energy supply in the form of glucose. It also participates in the preparation of the breasts for breastfeeding by stimulating the growth and differentiation of the mammary gland.

Secreted by the pituitary gland, prolactin gradually increases to be 5 to 10 times higher at the end of pregnancy. The glandular cells of the breasts then begin to secrete colostrum, a very nutritious liquid that will nourish the baby during his first days of life, before the flow of milk.

Oxytocin increases during pregnancy. In the last few weeks, it is secreted both by the pituitary gland of the mother and the fetus. Its role in triggering childbirth is debated: oxytocin would have a regulatory role but not an inducer. During labor, its secretion is periodic and brief and the frequency of peaks increases as labor progresses, with a maximum rate in the expulsion phase. After childbirth, oxytocin participates in uterine involution by helping the uterus to retract.

Oxytocin is used in synthetic form (Syntocinon) and intravenously to artificially trigger childbirth or to strengthen and regulate contractions. After expulsion, it is used to limit the risk of bleeding from the delivery.

Often referred to as the “attachment hormone”, oxytocin is thought to promote attachment between mother and baby. During breastfeeding, it also plays a key role by promoting the ejection of milk.