What hormone causes contractions of the uterus during labor

Hormones of pregnancy and labour

Introduction

The correct balance of hormones is essential for a successful pregnancy. Hormones act as the body’s chemical messengers sending information and feeding back responses between different tissues and organs. Hormones travel around the body, usually via the blood, and attach to proteins on the cells called receptors – much like a key fits a lock or a hand fits a glove. In response to this, the target tissue or organ functions in a way that ensures pregnancy is maintained. Initially, the ovaries, and then later, the placenta, are the main producers of pregnancy-related hormones that are essential in creating and maintaining the correct conditions required for a successful pregnancy.

The early stages of pregnancy

Following conception, a new embryo must signal its presence to the mother, allowing her body to identify the start of pregnancy. When an egg is fertilised, it travels though the female reproductive tract and implants into the womb around 9 days after it was fertilised, releasing a hormone called human chorionic gonadotrophin in the process. This hormone enters the maternal circulation and allows the mother to recognise the embryo and begin to change her body to support a pregnancy. This hormone continues to be produced in large quantities during pregnancy.

Human chorionic gonadotrophin can be detected in the urine as early as 7-9 days after fertilisation and is used as an indicator of pregnancy in most over-the-counter pregnancy tests. It is partly responsible for the frequent urination often experienced by pregnant women during the first trimester. This is because rising levels of human chorionic gonadotrophin causes more blood to flow to the pelvic area and kidneys, which causes the kidneys to eliminate waste quicker than before pregnancy. Human chorionic gonadotrophin passes through the mother’s blood to the ovaries to regulate the levels of the pro-pregnancy hormones, oestrogen and progesterone.

The role of progesterone and oestrogen during pregnancy

High levels of progesterone are required throughout pregnancy with levels steadily rising until the birth of the baby. During the first few weeks of pregnancy, progesterone produced from the corpus luteum (a temporary endocrine gland of the ovaries) is sufficient to maintain pregnancy. At this early stage, progesterone has many different functions which are vital to the establishment of pregnancy, including:

• Increasing blood flow to the womb by stimulating the growth of existing blood vessels.
• Stimulating glands in the lining of the womb (the endometrium) to produce nutrients that sustain the early embryo.
• Stimulating the endometrium to grow and become thickened, producing the decidua (a unique organ that supports the attachment of the placenta) and allowing implantation of the embryo.
• Helping to establish the placenta.

As the placenta forms and grows, it develops the ability to produce hormones. The cells that make up the placenta, known as trophoblasts, are able to convert cholesterol from the mother’s bloodstream into progesterone. Between weeks 6-9 of pregnancy, the placenta takes over from the ovaries as the main producer of progesterone. As well as being vital to the establishment of pregnancy, progesterone also has many functions during mid- to late pregnancy, including:

• Being important for correct foetal development.
• Preventing the muscles of the womb contracting until labour starts.
• Preventing lactation (breastfeeding) until after pregnancy.
• Strengthening the muscles of the pelvic wall in preparation for labour.

Although progesterone dominates throughout pregnancy, oestrogen is also very important. Many of the functions of progesterone require oestrogen and in fact, progesterone production from the placenta is stimulated by oestrogen. Initially, oestrogen is made and released by the corpus luteum of the ovaries. As the pregnancy develops, the foetal adrenal glands produce androgens that are then passed to the placenta and converted to the hormone oestriol (an oestrogen often used to determine foetal wellbeing in pregnancy) and other oestrogens. Levels of oestriol increase steadily until birth and have a wide range of effects, including:

• Maintaining, controlling and stimulating the production of other pregnancy hormones.
• Ensuring the correct development of many foetal organs including the lungs, liver and kidneys.
• Stimulating the growth and correct function of the placenta.
• Promoting growth of maternal breast tissue (along with progesterone) and preparing the mother for lactation (breastfeeding).

Other hormones produced by the placenta

The placenta also produces several other hormones including human placental lactogen and corticotrophin-releasing hormone. The function of human placental lactogen is not completely understood, although it is thought to promote the growth of the mammary glands in preparation for lactation. It is also believed to help regulate the mother’s metabolism by increasing maternal blood levels of nutrients for use by the foetus. Corticotrophin-releasing hormone is thought to regulate the duration of pregnancy and foetal maturation. For example, when pregnant women experience stress, particularly in the first trimester of pregnancy, the placenta increases the production of corticotrophin-releasing hormone. There is a good reason for this. In the first days of pregnancy, corticotrophin-releasing hormone suppresses the mother’s immune system, preventing the mother’s body from attacking the foetus. Later in pregnancy, it improves the blood flow between the placenta and foetus. In the last weeks of pregnancy corticotrophin-releasing hormone levels climb even higher – a rise which coincides with a major spike in cortisol levels. The rise in corticotrophin-releasing hormone and cortisol may help the foetal organs mature just before labour begins, and influence the timing of birth, through production of a ‘late-term cortisol surge’. This prenatal cortisol surge has also been linked to more attentive mothering in both animals and women. It is thought to be an adaptive response that induces an increased liking for their infant’s body odours, strengthening the bond between mother and baby.

Side-effects of pregnancy hormones

High levels of progesterone and oestrogen are important for a healthy pregnancy but are often the cause of some common unwanted side-effects in the mother, especially as they act on the brain. Until the mother’s body has adapted to the higher levels of these hormones, mood swings can be very common. The majority of women will experience morning sickness – a feeling of nausea, any time of day, which may lead to vomiting. The exact cause of morning sickness is unknown but it is likely to be because of the rapid increase in oestrogen, progesterone and human chorionic gonadotrophin, or a decrease in thyroid stimulating hormone (which has a similar structure to human chorionic gonadotrophin). Although it is probably caused by a combination of all these hormonal changes. Morning sickness usually starts around week 5-6 of pregnancy and often subsides by week 12-16, although some women suffer throughout pregnancy and/or have very severe forms of morning sickness.

Many women experience pain and discomfort in the pelvis and lower back during the first trimester. This is mostly due to a hormone called relaxin. Relaxin becomes detectable by week 7-10 and is produced throughout pregnancy. This hormone relaxes the mother’s muscles, joints and ligaments to make room for the growing baby. The effects of relaxin are mostly concentrated around the pelvic region, and softening the joints of the pelvis can often lead to pain in the area. Softer pelvic joints can also decrease stability and some women may notice it is harder to balance.

Although uncomfortable and frustrating at times, all these side-effects will usually lessen or even subside by the end of the first trimester.

Hormones and labour

The exact events leading up to the onset of labour are still not fully understood. For the baby to arrive, two things must happen: the muscles in the womb and abdominal wall have to contract and the cervix needs to soften, or ripen, allowing passage of the baby from the womb to the outside world.

The hormone oxytocin plays a key role in labour. Often called the ‘love hormone’, oxytocin is associated with feelings of bonding and motherhood. This is also true of another hormone released during labour called prolactin. If labour needs to be induced (brought on artificially), oxytocin or a synthetic oxytocin equivalent is often administered to ‘kick-start’ the process. Oxytocin levels rise at the onset of labour, causing regular contractions of the womb and abdominal muscles.

The cervix must dilate (open) to around 10cm for the baby to pass through. Oxytocin, along with other hormones, stimulates softening of the cervix leading to successive dilation during labour. Oxytocin, with the help of the high levels of oestrogen, causes the release of a group of hormones, known as prostaglandins, which may play a role in softening of the cervix. Levels of relaxin also increase rapidly during labour. This aids the lengthening and softening of the cervix and the softening and expansion of the mother’s lower pelvic region, thereby further aiding the baby’s arrival.

As labour contractions become more intense, natural pain relief hormones are released. Known as beta-endorphins, they are similar to drugs like morphine and act on the same receptors in the brain. As well as pain relief, they can also induce feelings of elation and happiness in the mother. As birth becomes imminent, the mother’s body releases large amounts of adrenaline and noradrenaline - so-called ‘fight or flight’ hormones. A sudden rush of these hormones just before birth causes a surge of energy in the mother and several very strong contractions, which help to deliver the baby.

Hormones after labour

When the baby is born, oxytocin continues to contract the womb in order to limit blood flow to the womb and reduce the risk of bleeding, and to help detach the placenta (which is delivered shortly afterwards). Blood levels of oxytocin and prolactin are very high, which supports bonding between the mother and baby. Skin-to-skin and eye contact between the mother and baby also stimulate the release of oxytocin and prolactin, further encouraging bonding. Many mothers describe being in a euphoric state just after labour; this is due to the effects of oxytocin, prolactin and beta-endorphins.

Women are actually able to breastfeed at around four months of pregnancy but high levels of progesterone and oestrogen during this time prevent milk production. After the placenta is delivered during birth, the blood levels of progesterone and oestrogen fall, allowing the mother to produce the first meal of colostrum, a high density milk that contains more protein, minerals and fat-soluble vitamins (A and K) than mature milk, which is produced later. When the baby suckles, oxytocin and prolactin are released from the pituitary gland, and pass through the mother’s blood to the breast, where prolactin stimulates milk production and oxytocin stimulates milk delivery to the nipple. As well as stimulating bonding, these hormones also aid milk release and further milk production. Mature milk that nourishes the baby and induces sleep starts to be produced about four days after birth.

Last reviewed: Mar 2021

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Hormones and fetal growth

The Role of Hormones in Childbirth

You (and your baby) are born with the ability to start labor, labor and give birth, breastfeed and become deeply attached to each other. The flow of hormones in your body drives these well-organized, finely tuned processes.

It is important that you and your maternity care providers understand how to work with — and avoid disrupting — these processes.

While you don’t need to be taught how to give birth, it is fascinating to learn about the amazing capabilities of women and newborns. For example, a newborn who was not exposed to pain medications and is placed skin-to-skin on his or her mother right after birth can crawl to mom’s breast and begin nursing!

The Role of Birth Hormones

Birth hormones are chemical “messengers” that your body makes. Your baby makes birth hormones, too. These hormones work together to guide important changes in your bodies — changes that help make labor and birth go smoothly and safely for both of you.

Birth hormones help guide you and your baby in many ways, including:

• Getting your body ready to give birth
• Starting your labor contractions
• Preparing your baby for labor and life outside your body
• Telling your breasts to make milk and getting your baby ready to breastfeed

And when you and your new baby fall in love, birth hormones are part of those feelings, too!

Here we discuss four hormones that are important for reproduction: oxytocin, endorphins, adrenaline and related stress hormones, and prolactin. These hormones play a major role in regulating labor and birth. Learning about them can help you understand what will happen during labor and birth. Decisions you make about your care can support or disrupt the way hormones work, so understanding how they work and how they are affected is important for making informed decisions.

Oxytocin

Oxytocin is often known as the "hormone of love" because it is involved with lovemaking, fertility, contractions during labor and birth and the release of milk in breastfeeding. It helps us feel good, and it triggers nurturing feelings and behaviors.

Receptor cells that allow your body to respond to oxytocin increase gradually in pregnancy and then increase a lot during labor. Oxytocin stimulates powerful contractions that help to thin and open (dilate) the cervix, move the baby down and out of the birth canal, push out the placenta, and limit bleeding at the site of the placenta. During labor and birth, the pressure of the baby against your cervix, and then against tissues in the pelvic floor, stimulates oxytocin and contractions. So does a breastfeeding newborn.

Low levels of oxytocin during labor and birth can cause problems by:

• Causing contractions to stop or slow, and making labor take longer.
• Resulting in excessive bleeding at the placenta site after birth.
• Leading health care providers to respond to these problems with interventions.

You can promote your body's production of oxytocin during labor and birth by:

• Staying calm, comfortable and confident.
• Avoiding disturbances, such as unwelcome people or noise and uncomfortable procedures.
• Staying upright and using gravity so your baby is pressed against your cervix and then, as the baby is born, against the tissues of your pelvic floor.
• Stimulating your nipples or clitoris before birth, and giving your baby a chance to suckle (breastfeed) shortly after birth.
• Avoiding epidural analgesia.

Endorphins

When you face stress or pain, your body produces calming and pain-relieving hormones called endorphins. You may have higher levels of endorphins near the end of pregnancy. For women who don’t use pain medication during labor, the level of endorphins continues to rise steadily and steeply through the birth of the baby. (Most studies have found a sharp drop in endorphin levels with use of epidural or opioid pain medication.)

High endorphin levels during labor and birth can produce an altered state of consciousness that can help you deal with the process of giving birth, even if it is long and challenging. High endorphin levels can make you feel alert, attentive and even euphoric (very happy) after birth, as you begin to get to know and care for your baby. In this early postpartum period, endorphins are believed to play a role in strengthening the mother-infant relationship. A drop in endorphin levels at this time may contribute to the "blues," or postpartum depression, that many women experience for a brief time after birth.

Low levels of endorphins can cause problems in labor and birth by:

• Causing labor to be excessively painful and difficult to tolerate.
• Leading health care providers to respond to this problem with interventions.

You can enhance your body's production of endorphins during labor and birth by:

• Staying calm, comfortable and confident.
• Avoiding disturbances, such as unwelcome people or noise and uncomfortable procedures.
• Delaying or avoiding epidural or opioids for pain relief.

Adrenaline

Adrenaline is the "fight or flight" hormone that humans produce to help ensure survival. Women who feel threatened during labor (for example, by fear or severe pain) may produce high levels of adrenaline. Adrenaline can slow labor or stop it altogether. Earlier in human evolution, this disruption helped birthing women move to a place of greater safety.

Too much adrenaline can cause problems in labor and birth by:

• Causing distress to the baby before birth.
• Causing contractions to stop, slow or have an erratic pattern, and lengthening labor.
• Creating a sense of panic and increasing pain in the mother.
• Leading health care providers to respond to these problems with cesarean surgery and other interventions.

You can keep adrenaline down during labor and birth by:

• Staying calm, comfortable and relaxed.
• Being informed and prepared.
• Having trust and confidence in your body and your capabilities as a woman.
• Having trust and confidence in your care providers and birth setting.
• Being in a calm, peaceful and private environment and avoiding conflict.
• Being with people who can provide comfort measures, good information, positive words and other support.
• Avoiding intrusive, painful, disruptive procedures.

Prolactin

Prolactin is known as the “mothering” hormone. The role of prolactin around the time of birth has been less researched than the hormones described above. It increases during pregnancy and peaks when labor starts on its own. As has been shown in other mammals, continued prolactin production during and after labor appears to be readying a woman’s body for breastfeeding. It may also play a role in moving labor along and helping the newborn adjust to life outside the womb. Prolactin is central to breast milk production. High levels of prolactin with early breastfeeding may foster women’s caretaking behaviors and adjustment to being a mother. This hormone may also support the infant’s healthy development.

Low levels of prolactin may cause problems through:

• Poorer transition of the baby at the time of birth.
• Poorer growth and development of the baby.
• Poorer adjustment of a woman to motherhood.

You can likely promote your body’s production of prolactin by:

• Waiting for labor to start on its own.
• Minimizing stress during labor and after birth.
• Keeping woman and baby together after birth.
• Breastfeeding early and thereafter on cue from the baby.

Maximizing the Role of Birth Hormones

As you can probably tell from the information above, some features of typical hospital childbirth settings, like noise or medical interventions, can interfere with your body’s natural processes. To avoid this and maximize your body’s ability to follow its natural processes, it’s a good idea to seek out a birth setting that supports this. Out-of-hospital birth settings and one-on-one continuous labor support, such as doula care, can help create conditions that enhance your body’s natural production of helpful hormones and keep disturbing hormones in check.

You can read more about the role of hormones in childbirth in the Pathway to a Healthy Birth booklet.

10 little helpers: what hormones are involved in childbirth - Parents.ru

Pregnancy

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obstetrician-gynecologist

To explain the mechanism of labor, scientists put forward many theories. The most interesting one is from the Dutch neuroscientist Dick Swaab. In his opinion, the signal for the onset of labor is given by a decrease in the level of glucose in the blood of the unborn baby. As the mother's body is no longer able to provide adequate nutrition to the growing baby, a series of hormonal changes occur that cause uterine contractions. But recently, another hypothesis has been gaining more and more supporters. The main reason for timely delivery, she calls the genetic program, which provides for the completion of pregnancy as soon as the unborn baby is ready for autonomous existence. In any case, mother and baby cannot do without helpers. They become hormones. nine0003

First Aid

Childbirth begins with "forerunners". At this point, the level of progesterone in the woman's body begins to decrease. This hormone is produced by the placenta. He is the "guardian" of pregnancy, suppressing the contractility of the uterus and maintaining the tone of the cervix. As the level of progesterone decreases, the uterus, which for the time being was relaxed, becomes sensitive and tense. Mom feels the movements of the baby more and more sharply, at times tension arises in the lower abdomen, slight contractions of the uterus are felt. nine0003

At the same time, the level of estrogen in a woman increases - this is how the female sex hormones estradiol, estrone and estriol are generally called. They contribute to the maturation of the cervix. Under their influence, it softens, shortens and begins to gradually open up. Thanks to estrogen, the tone of the uterus also increases and the preparation of the soft birth canal begins for the birth of the baby. In addition, female sex hormones inhibit the activity of specific enzymes that destroy oxytocin. He is called the "king of childbirth". And not in vain. This hormone is the strongest stimulator of uterine contractions. At the same time, prostaglandins are formed in the tissues of the placenta, the walls of blood vessels, ovaries, intestines, lungs, in the fallopian tubes, in the wall of the stomach and even in the muscle of the heart, but most of them are produced in the tissues of the uterus. Interestingly, these biologically active substances, close to hormones, were first discovered in the male gonads (“prostaglandins” - a derivative of the word “prostate”). They also cause uterine contractions, soften the cervix and start labor. nine0003

Serotonin is also involved in the regulation of labor activity. It acts directly on the receptors located in the myometrium (one of the layers of the uterus), activating them, plus through the central nervous system increases the production of oxytocin. The concentration of serotonin in the blood, uterus and placenta increases with increasing gestational age and reaches a maximum by the time of delivery.

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Developments

So, prostaglandins “trigger” the mechanism of contractions, and oxytocin helps to keep them normal. Its powerful release into the blood occurs at the very beginning of childbirth, then another one, after which the cervix begins to open faster. As soon as it opens completely, the third surge of this hormone will make the woman push, "pushing" the child to the "exit". And, finally, “at the end” of the process, oxytocin is needed so that the contractions do not fade away and the separated placenta, along with the fetal membranes, leaves the body of a young mother. nine0003

Natural pain relief

But this is not all the hormones and biologically active substances that help a woman cope with a difficult task and give birth to a baby. In the reserves of our body there is a whole arsenal of tools that reduce pain and tension. We are talking about the so-called pleasure hormones - endorphins. The adrenal hormones cortisol and catecholamines, the production of which is stimulated by adrenocorticotropic hormone, also help to cope with the difficulties of childbirth. Together with endorphins, they “balance” the stress hormones adrenaline and norepinephrine. The last substances during childbirth also do not remain behind the scenes. Before the start of the attempts, when the woman has already spent a lot of energy to survive the contractions, and is rather tired, thanks to a sharp release of adrenaline, she has a “second wind” and the strength to push. nine0003

It is believed that the signal for the onset of labor is given by the unborn baby. In his blood, the level of corticosteroids increases, which, in turn, stimulate the production of estrogens and prostaglandins.

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Difficulties are overcome

Childbirth will take place as prescribed by nature, only when each of the hormones starts working at the right time and its concentration is sufficient. Even the smallest failure in this system can disrupt the normal course of events. For example, due to a lack of estrogen, the process of preparing for childbirth and maturation of the cervix may be delayed. In this case, doctors talk about a "post-term" pregnancy, and childbirth begins after 41 weeks. nine0003

With a deficiency of prostaglandins, difficulties begin with the maturation of the cervix. If for some reason this has not yet happened by the time of birth, synthetic analogues of these biologically active substances are used. In Russia, a vaginal gel is registered, which is allowed to be used in such cases. Also, with a deficiency of prostaglandins, the preparatory stage of childbirth is lengthened. It usually lasts up to 6 hours. During this period, a woman feels light, almost imperceptible irregular contractions. But if her body produces few necessary hormones, the process is delayed, the woman in labor gets very tired. nine0003

Deficiency of oxytocin complicates not only the preparatory period, but also the very process of the birth of a child. With this turn of events, the muscles contract weakly, the cervix opens slowly. Because of this, the child moves through the birth canal for a very long time. Doctors talk about the weakness of labor and can introduce a synthetic analogue of oxytocin into the woman's body. You should not be afraid of such manipulations: everything is done only with the written consent of the future mother, and the goal is the same - to help the baby be born healthy. Moreover, in this way, the most formidable complication is prevented, which is very rare, but can occur at the last stage of childbirth - hypotonic bleeding. nine0003

There is also a situation when oxytocin is produced in excess. Childbirth then takes place too rapidly, the baby moves very quickly towards the “exit”. As a result, he, having no time to prepare, can get injured, and his mother can get soft tissue ruptures.

Look into your plate

Hormone levels are corrected during childbirth with the help of droppers or injections. It is possible to speak about the prevention of such troubles with a certain degree of conventionality, because often the problem does not manifest itself until X hour. But if you eat right, the chances that pregnancy and childbirth will pass without complications increase dramatically. After all, the prostaglandins needed during childbirth are synthesized in the body from polyunsaturated fatty acids (PUFAs). Their sources are vegetable oils: linseed, olive, almond. nine0003

Many of these acids are also found in fish oil, pine nuts, walnuts, trout, salmon, tuna, halibut and Omega-3, -6, -9 vitamins. In addition to prostaglandins, the production of natural oxytocin is also stimulated by magnesium and vitamins D, C. These nutrients are abundant in dates, pomegranates, bananas and avocados. That's why the expectant mother needs to watch what she eats and listen to the recommendations of her doctor.

More interesting and useful materials about the health of the expectant mother are in our channel on Yandex.Zen. nine0063