How Pregnancy Hormones Affect Each Trimester
Expecting a baby brings big changes, many of which stem from shifting hormone levels. During each trimester, the body releases different hormones that support pregnancy and prepare for birth.
These hormones affect physical and emotional well-being. Common changes include mood swings, tiredness, and nausea, but each stage of pregnancy brings something new. Understanding how these hormonal shifts unfold can help you navigate the journey with more confidence and clarity.
Hormones and Body Changes Early in Pregnancy
In the first trimester, hormone levels change quickly to support the new pregnancy. Progesterone and estrogen increase, helping the uterus get ready and maintain the pregnancy. These hormones can cause mood swings, tiredness, and headaches. Human chorionic gonadotropin (hCG) rises fast and can lead to morning sickness, nausea, and vomiting.
Hormone shifts can also cause heartburn and skin changes. Many people feel more tired and may notice stronger headaches. Hormone changes increase blood flow and change how the immune system works, all to support the pregnancy.
Progesterone
Progesterone prepares the uterus for the fertilized egg by thickening the uterine lining. This hormone relaxes muscles, making sure that the uterus does not contract until labor.
Progesterone slows digestion, which can lead to constipation. Because levels stay high during pregnancy, some people notice mood changes like irritability or mood swings. These shifts can show up as sudden changes in emotions, such as feeling angry one moment and sad the next.
Estrogen
Estrogen supports the developing baby by keeping the uterine lining healthy. This lining, also known as the endometrial lining, is where the embryo grows and receives nutrients. Estrogen and progesterone work together to keep this lining strong and stable.
Estrogen boosts blood flow throughout the body, carrying more nutrients and oxygen to both mother and baby. Many women notice their breasts feel more sensitive and tender due to the extra blood supply.
Increased blood flow can make the nasal passages swell, often leading to a stuffy or runny nose. The kidneys filter extra fluid, causing more frequent bathroom visits. Extra pressure from the growing uterus on the bladder adds to this.
Some people notice their skin takes on a brighter, healthier look, often called the “pregnancy glow.” Higher blood flow and the effects of estrogen on skin cells contribute to this change.
HCG
After conception, the body produces human chorionic gonadotropin (hCG), a hormone usually only present during pregnancy. Home pregnancy tests check for this hormone in urine, providing an early way to confirm pregnancy. The body increases hCG levels quickly, doubling about every two to three days and peaking between eight and 11 weeks.
The placenta develops as hCG rises, providing nutrients and support to the growing fetus. Higher concentrations of hCG often cause first-trimester symptoms, most notably nausea, sometimes called morning sickness. The more hCG a person produces, the more likely they may be to experience this nausea. Pregnancies involving twins or multiples often produce even higher amounts of hCG, making nausea more common and sometimes more intense.
Many individuals notice a stronger sense of smell during this time, which may relate to increased hCG levels. For many, nausea and related symptoms ease as hCG levels fall after their early peak, usually as the second trimester begins.
TSH
The pituitary gland in the brain creates thyroid-stimulating hormone (TSH). TSH controls the thyroid’s activity by signaling it to produce hormones that manage metabolism in every cell. During pregnancy, the body needs more thyroid hormones to help the baby’s brain and bones develop.
Higher levels of hCG and estrogen, common in pregnancy, stimulate the thyroid gland even more, especially with twins or multiples. This activity ensures enough thyroid hormones are available for both mother and child.
Doctors monitor TSH and related thyroid hormones by taking blood tests during the first trimester. If there is a known thyroid condition or abnormal test results, these checks might happen every few weeks. Sometimes, those with abnormal thyroid levels visit an endocrinologist for further care and advice.
Hormonal Changes During the Second Trimester
During the second trimester, estrogen and progesterone keep rising, and relaxin becomes more active. Relaxin loosens the ligaments in the pelvis and prepares the uterus for continued growth, but it can also lead to backaches or tightness in joints. Many women notice pain in their hips, lower back, or pelvis, which can make daily activities harder.
Hormone changes often cause trouble sleeping. Many people wake up often or struggle to get comfortable at night. The hormone shift may also lead to more frequent bathroom visits, as the growing uterus puts extra pressure on the bladder.
Some women notice that their nose bleeds more easily or that their appetite changes. Quickening, or the first awareness of fetal movement, usually happens at this stage. Doctors often recommend taking prenatal vitamins that include vitamin B6, which can support energy and help with pregnancy health. Gestational diabetes may also be checked for in this trimester, as hormones can affect blood sugar levels.
Melasma
Higher levels of estrogen and progesterone during pregnancy can change skin pigmentation. These hormones stimulate melanocyte production, increasing melanin and causing brown or grey patches on areas like the cheeks, forehead, and upper lip. This common skin condition is often called the “mask of pregnancy.” Melasma usually fades after childbirth, though the timing varies for each person.
Other skin changes can occur at the same time. Many women see a dark vertical line, known as the linea nigra, running up their abdomen. Nipples, moles, and freckles may also darken. Increased hair growth is another effect, linked to hormonal shifts.
Cortisol
Cortisol naturally rises during pregnancy and supports the growing baby. This hormone helps the mother’s body manage metabolism and keeps blood sugar in check. Higher levels can bring extra symptoms, including skin changes such as stretch marks, increased facial redness, and sometimes issues with blood pressure.
Human Placental Lactogen
Human placental lactogen (HPL) comes from the placenta during pregnancy. HPL helps the developing baby get the nutrients it needs. One of HPL’s main roles is to make pregnant women less sensitive to insulin, keeping blood sugar higher for longer. This process helps more glucose reach the baby through the placenta.
As pregnancy enters the second trimester, this change in insulin response can sometimes cause gestational diabetes. When insulin resistance increases, the baby may get more sugar than needed, leading to faster growth. The body uses this system as an adaptation, helping babies get the right amount of energy during times of growth.
Hormonal Changes in the Final Trimester
In the final months of pregnancy, estrogen and progesterone reach their peak levels, with estrogen rising to nearly six times its usual amount. This increase prepares the body for labor and life after childbirth. The growing fetus also triggers other hormones, such as relaxin, which loosens the muscles and ligaments in the pelvis for delivery.
A boost in estrogen can cause swelling, especially in the ankles and feet, by affecting how the body manages salt and water, leading to more fluid retention and edema. Progesterone continues to relax muscles throughout the body, including the digestive tract, which can slow down digestion and cause symptoms like heartburn or acid reflux.
Lightening, or the baby moving lower into the pelvis, can be influenced by hormonal shifts in these final weeks. Women may notice more vaginal discharge, another result of changing hormone levels, which helps protect against infection as labor nears. Braxton Hicks contractions may occur more often, signaling that the body is getting ready for labor.
Prolactin
Prolactin becomes much more active as pregnancy progresses, especially in the third trimester. By this point, prolactin levels can reach up to 10 times higher than at the start of pregnancy. This increase supports changes in breast tissue, preparing the body for milk production once the baby is born. Even before birth, the breasts start making a special early milk called colostrum, and sometimes small leaks can begin in the weeks before delivery.
Actual milk production starts after delivery, when progesterone and estrogen drop. This sudden change allows prolactin to direct the start of milk making for the newborn. Health experts suggest keeping nursing pads on hand during this stage, as early colostrum leakage can occur and continue into the first days after the baby arrives.
While prolactin is not the only hormone at work, its main function is getting the breasts ready to nourish the baby once childbirth happens.
Changes in Hormones After Birth
After childbirth, hormone levels shift quickly. In the first day, endorphins are high, which can help someone feel a sense of accomplishment and even excitement after delivery. This boost is short-lived, and by days three and four, hormone levels start dropping as the body adjusts to life without the placenta. Hormones like estrogen, progesterone, relaxin, hCG, and HPL all decrease at this time.
Estrogen and progesterone reach their lowest points since before puberty. This quick drop can make people feel sad or moody, often called the “baby blues.” Lack of sleep, which is common for new parents, makes things harder because it raises cortisol, the hormone connected to stress. Feeling tired, stressed, and emotional is normal in these first weeks.
Oxytocin stands out after birth. The body releases it during time with the baby or skin-to-skin contact. Oxytocin helps with bonding and calm, and it can help the uterus contract. For some, oxytocin also helps balance sadness and stress.
Prolactin is key for breastfeeding. When the baby suckles, prolactin rises and tells the body to produce milk. Nighttime feedings can be tough, but they raise prolactin and support the milk supply. Lactation depends on this feedback loop between the baby’s needs and the parent’s hormones.
Oxytocin
Oxytocin is a hormone that plays a central role after childbirth, especially in activities like breastfeeding and close physical contact. When a mother breastfeeds or holds her baby skin-to-skin, her body releases oxytocin.
This hormone often fosters emotional bonding and helps new parents feel more connected to their baby. Besides its role in bonding, oxytocin also aids in the milk letdown process, making it easier for mothers to feed their newborns.
However, oxytocin has other effects too. The same hormone that supports milk flow can also cause the uterus to contract. For some mothers, these contractions feel like mild to moderate cramps, particularly in the first weeks after delivery. These sensations are normal and typically lessen as the body continues to recover from childbirth. Once breastfeeding ends and the menstrual cycle returns, hormone levels gradually adjust.
Understanding how hormones like oxytocin shape bonding and recovery after childbirth can make the early days of parenting more manageable. Regular skin-to-skin contact and frequent breastfeeding not only strengthen emotional connections but also support physical healing. By recognizing these natural shifts, new parents can navigate challenges with greater confidence and care.
