All about Hormones During Pregnancy

Hormones During Pregnancy - The changes in hormone levels in pregnant women are truly profound. Most men find it difficult to fully comprehend what is causing all these changes from mood swings to constipation, extra sleep to food cravings.

Quite simply, it is the effect of various hormones that is the main contributor to these changes in your partner, but more than that, it's these very same hormone changes that enable her to carry the baby for nine months and assist it to develop.

In a previous article, we discussed in detail the role of the vital hormone b-HCG (beta Human Chorionic Gonadotropin hormone) during pregnancy, then in another issue, we discussed the effects of the hormones produced in the pituitary gland,

LH (luteinizing hormone) and FSH (Follicle Stimulating Hormone) during the ovulation process.

This new piece expands the subject to cover progesterone and estrogen (estrogen), as well as some other lesser well-known hormones.

The precise, intricate interactions between all of the various hormones swimming around her body are still to be fully explained. However, a large part of the primary functions of each hormone is understood, and research is continuing on mapping out the full picture.

The introduction of Hormones During Pregnancy:

1. Progesterone production

Progesterone is found at relatively low levels for the first part of a woman's menstrual cycle. It is produced by cells in the ovaries called "granulosa cells" which surround the tiny follicles that will mature to become ovulated eggs.

After ovulation, the "yellow body" (corpus luteum = Once a follicle has been impregnated, it breaks open to expose the egg. The follicle quickly transforms into the Yellow Body and begins to secrete progesterone and estrogen which is used to alert the uterus wall and stimulate it to produce a mucus lining capable of accepting a fertilized egg) that released the mature egg into the Fallopian tube begins to secrete high levels of progesterone from the granulosa cells within it.

This hormone stimulates the growth of rich blood vessels that supply the uterus lining (endometrium). It also causes the expansion of tiny glands in the endometrium that produce a fluid (uterine fluid) that can be used to nourish sperms and embryos that find their way into the uterus. These tiny glands are created by the estrogen hormone and the progesterone takes over the job of making them mature into "feeding structures".

The production of progesterone will normally drop away after about 10 days beyond ovulation. It is this sudden reduction in the hormone that will prompt the menstruation period to begin due to the reduced oxygen supply from the blood vessels that were previously encouraged to grow by the progesterone hormone.

If however, the released egg is fertilized and manages to embed itself into the uterine wall, then the hormone b-HCG is released from the developing placenta, which has the effect of telling the "yellow body" to continue to produce both progesterone and estrogen. This, in turn, prevents the start of the menstrual cycle and stops further eggs from being released.

The ovaries continue to produce progesterone (and estrogen) during the first 8 to 9 weeks until the placenta begins to reduce the amount of b-HCG secreted, which is a signal to the "yellow body" that it is capable of producing these hormones for itself and requires less help.

2. The role of progesterone

The placenta continues to produce both progesterone and estrogen for the duration of the pregnancy and the levels get higher and higher right up to just before the birth.

The following chart shows the average growth in the level of progesterone within the body during a pregnancy. The dotted line shows what would happen if no fertilization happened during normal menstrual cycles.

The Role Of Progesterone

During the pregnancy, the progesterone is needed in the following ways, (mostly in conjunction with estrogen):

  • Makes the endometrium develop and secrete fluids after being primed by estrogen
  • Maintains the functions of the placenta and fights off unwanted cells near the womb that could cause damage to the placenta or fetus.
  • Keeps the endometrium in a thickened condition
  • Stops the uterus making spontaneous movements
  • Stimulates the growth of breast tissue
  • Prevents lactation until after the birth (with estrogen)
  • Strengthens the mucous plug covering the cervix to prevent infection.
  • Strengthens the pelvic walls in preparation for labor.
  • Stops the uterus from contracting (thus keeping the baby where it is)

At the end of the pregnancy, the levels of progesterone secreted by the placenta drop off. It is this action that stimulates the beginning of the contractions that will lead to birth.

The effects on a woman due to raised levels of progesterone can include any or all of the following:

  • Constipation
  • Heartburn
  • Runny and irritable nose
  • Eyesight problems (blurring or headaches)
  • Increased kidney infection risk.

A minimum level of about 10ng/ml is required to sustain a pregnancy through the very early stages. It is because of this that doctors can measure the levels of progesterone in the blood to assist in the diagnosis of abnormal pregnancies such as ectopic pregnancy.

Supplements of natural progesterone are sometimes prescribed as a fertility treatment or to assist in reducing the risk of miscarriage. This is found in the form of a cream that is rubbed into the abdomen and thighs or else it arrives as a vaginal suppository or an injection (tablets don't work very well).

3. The role of estrogen (estrogen)

Estrogen is the name given to a family of ovarian hormones which all have similar characteristics. During the female menstruation cycle, the production of estrogen is controlled by the hormone LH (Luteinizing Hormone = A hormone produced in the anterior lobe of the pituitary gland.  In women, it stimulates the maturation of the follicle and causes the production of the "Yellow Body".  In men, the same hormone stimulates the testis to produce testosterone. (LH is called ICSH in men) both indirectly and directly. The "Yellow Body" (corpus lutem) is directly stimulated by LH to produce estrogen, whereas, before ovulation, the granulosa cells of the follicle are stimulated to produce estrogen via an enzyme called aromatic.

As with progesterone, estrogen is produced by the placenta throughout a pregnancy and the levels increase steadily until birth.

Each hormone plays a vital and complex role during a pregnancy and many of them interact with each other to stimulate various parts of the process.

One role of estrogen during pregnancy is to regulate the production of progesterone over the full term. As estrogen is produced by the placenta, progesterone production is stimulated and regulated.

Apart from this, estrogen plays a very important role in the development of the fetus. Without estrogen, the lungs, kidneys, liver, adrenal glands and other organs would never be triggered into maturation. In fact, the placenta itself would never grow and operate properly if not for estrogen.

The following list shows some other known jobs undertaken by estrogen:

  • Triggers the maturation of reproductive organs
  • Help in the development of sexual characteristics
  • Assists in the lactation process
  • Regulates bone density in a fetus
  • Maintains the endometrium during pregnancy
  • Promotes blood flow to the uterus
  • Maintains, regulates and triggers the production of other hormones
  • Protects female fetuses from the effects of androgens in the mother's system. (Androgens are substances that have a masculinizing effect).

The main external effect on women of the increased levels of estrogen during a pregnancy is the appearance of rashes or red blotches on the skin. It is this effect that is often described as the 'glow' of pregnancy.

4. Summary of some other hormones during pregnancy

The following list gives a quick summary of the primary function of the other Hormones During Pregnancy that has not been discussed up to now:

  1. HSC (Human Chorionic Somatomammotropin) or HPL (Human Placental Lactogen) - This hormone is regulated by estrogen and is produced within the placenta. It plays a part in the development of the fetus and helps the breasts develop the glands that will be required for breastfeeding. It also reduces the level of glucose consumed by the mother. The levels increase steadily from 3 weeks gestation to a limit in the last month of pregnancy.
  2. Calcitonin - This protein based hormone is used to regulate the bone development and to stop calcium from transferring from the bones into the blood system.
  3. Thyroxine (T4 & T3) - This is needed for the development of the central nervous system. It also increases oxygen consumption and develops the ability of the fetus to metabolize proteins and carbohydrates. On top of this, it interacts with growth hormones to regulate and stimulate the baby's growth.
  4. Insulin - Helps the baby to store food in its body and to regulate glucose levels.
  5. Relaxin - encourages the cervix and the pelvic muscles to relax, thus helping with labor and birth.
  6. Oxytocin - This hormone is released as a response to stretching the cervix or stimulation of the nipples. It has the effect of making the uterus contract so that birth happens rapidly. It also stimulates the mammary glands to produce milk. High levels of progesterone will prevent oxytocin from having an effect. Only when progesterone levels drop close to the birth will the effects of this hormone be felt.
  7. Erythropoietin - Produced in the kidneys, this hormone looks after bone marrow and red blood cell production.
  8. Cortisol - Helps the baby use various foods properly within the body.
  9. Prolactin - This hormone is made by the baby's kidneys and is reduced about a week after birth. The levels remain high within the mother's blood for about two weeks after birth. Prolactin is important for the regulation of the mother's metabolism during the pregnancy and assists in the stimulation of immune system cell growth. It helps prepares the breasts for breastfeeding and promotes the growth of the baby.

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