The Bottom Line

Pregnancy (at implantation) causes a rapid release of reproductive hormones. These hormones tell the body what to do and how to change.

Numerous organ systems within the body have receptors for these hormones (think lock and key) which is why women can experience so many different signs and symptoms in early pregnancy, including those that seemingly have nothing to do with pregnancy.

These symptoms also vary widely among women because women respond differently to these hormones. While some women can experience multiple signs and symptoms almost immediately, others many not notice anything for weeks (other than a missed period).

Women should call their health care provider (HCP) as soon as they learn they are pregnant or if they think they might be pregnant. Physical signs and symptoms are not sufficient on their own to diagnose pregnancy.

Women should also call their HCP if any symptoms start to become more than they can handle (nausea, vomiting, headaches, extreme fatigue) or if they experience abdominal pain, which could indicate other conditions that need to be ruled out.

For signs and symptoms related to ovulation and implantation, click here.

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Early pregnancy symptoms are very similar to pre-menstrual symptoms since many of the same hormones are involved (estrogen, progesterone), but levels of these hormones increase exponentially starting immediately after implantation.

Although there are critical differences between true early pregnancy symptoms and menstrual symptoms, at least one study identified there could be a link regarding severity (and number) of symptoms:

In this particular study, the severity of premenstrual symptoms was significantly associated with the overall severity of early pregnancy symptoms. Therefore, women who tend to experience more symptoms during their menstrual cycles (“hormone sensitivity”) may experience more early pregnancy symptoms (but this is likely not the case for all women).


While estrogen and progesterone are responsible for most menstrual symptoms, human chorionic gonadotropin (HCG) – which is only made in pregnancy – starts the cascade of early pregnancy symptoms.

HCG is produced by the trophoblasts of the developing placenta. After implantation, the embryo actively secretes this hormone, which can be detected in the mother’s blood as early as eight days after ovulation.

HCG is the first hormone that lets the body know a pregnancy has occurred; once this hormone is detected, the rest of the body begins changing to support the pregnancy to include releasing additional hormones (estrogen, progesterone – but at much higher levels than during a normal cycle).

Learn more about HCG and pregnancy, including HCG levels.

Symptoms and Timing

Two or more symptoms between 4 and 8 weeks of pregnancy are common and can include (in addition to a missed period):

  • Spotting (light vaginal bleeding; may be mistaken for a period)

  • Constipation/bloating

  • Fatigue

  • Nausea

  • Vomiting

  • Shortness of breath

  • Dizziness

  • Breast tenderness

  • Varicose veins

  • Hot flashes/sweating

  • Skin changes

  • Headache

  • Hunger

  • Trouble sleeping

  • Nasal congestion*

  • Frequent urination*

  • Back pain*

  • Acid Reflux/heartburn*

*Although commonly known to occur later in pregnancy, these four symptoms surprisingly also occur very frequently in the first trimester.

It is assessed the earliest and most obvious symptoms likely do not begin until after key stages of early embryonic development (5 to 7 weeks), although some women may experience signs or symptoms before this time.

In a study of 136 pregnant women, half began experiencing symptoms by day 36 after their last menstrual period (approximately 5 weeks of pregnancy) and 89% by the end of the 8th week.

Interestingly, women who smoked tobacco or marijuana tended to have delayed onset of symptoms.

Symptoms and Risk of Miscarriage

Current research indicates the presence of symptoms is not necessarily a good indicator of miscarriage risk (although nausea/vomiting may be exceptions).

A lack of physical symptoms early in pregnancy does not necessarily mean a pregnancy is in danger. Further, women who experience symptoms early in pregnancy may go on to later miscarry (Sayle, et al. 2002).

Missed Period

Pregnancy causes the menstrual period to stop. A “missed” expected period is normally one of the very first signs of pregnancy for most women who are aware of their cycle.

The release of HCG causes the corpus luteum (formed in the ovary at the site of where the egg was released during ovulation) to continue producing progesterone to support the pregnancy.

If implantation does not occur, the corpus luteum dies, progesterone drops, and menstruation begins (and the cycle starts over). HCG essentially “rescues” the corpus luteum to keep progesterone levels high for the growing embryo – and no period.

Vaginal Bleeding

Although pregnancy stops menstruation, women may still experience bleeding in early pregnancy; some women may even confuse this for their period.

Implantation, by itself, can lead to light bleeding usually described as brownish in color (due to it being “older” blood) and is likely to occur closer to a woman’s expected period.

There is very little research on implantation bleeding and although it can happen, it does not appear to be very common.

Light pink or red spotting can also occur for reasons that are mostly unknown in early pregnancy. If this bleeding does not get heavier or eventually stops, it is likely not of concern, but this is difficult to determine based on bleeding alone.

Bleeding that is heavier than spotting also does not necessarily mean that miscarriage is imminent, but it does indicate a higher risk.

Read more detail about Vaginal Bleeding in early pregnancy.

It is recommended that women call their health care provider anytime they experience bleeding in early pregnancy. This assessment is also critical to rule out possible ectopic pregnancy.


The cardiovascular system is the first major maternal organ system to experience changes. These changes are necessary due to the now increased blood and oxygen requirements in the body (oxygen is carried by the blood).

Between 4 and 7 weeks of pregnancy, blood volume, heart rate, and the amount of blood the heart can pump in one-minute all increase. These cardiac adjustments can lead to significant and almost immediate energy depletion.

Blood volume increases by about 1.5 liters. Since the pregnant body has more blood (mostly plasma), more blood is pumped out with each heart contraction; overall heart rate increases to carry this oxygen – causing fatigue.

Women can experience an increase in resting heart rate (10 to 20 beats per minute) which could start as early as 4 weeks, continuing until term. This increase in heart rate could result in an extra 14,000 to 28,000 beats per day. Twin pregnancies may accelerate heart rate even further.

By 8 weeks, the heart pumps about 25% more blood in one minute than before pregnancy. As heart rate has increased, it takes less effort to become “out of breath” as the cardiovascular system is already working much harder than before pregnancy.

Blood pressure drops slightly due to the increased blood circulation to the fetus and placenta, exacerbating feelings of fatigue.

Along with fatigue, these normal early changes also lead to symptoms such as shortness of breath, bloating, and dizziness. (Note: These are also symptoms of anemia; a lack of red blood cells means the body cannot adequately transport oxygen, a common finding in pregnancy.)

Learn more about Fatigue and Exhaustion in pregnancy.

Photo by Mel Elías on Unsplash

Bloating and Constipation

Bloating is very common in early pregnancy for two major reasons:

The slight decrease in blood pressure described above triggers the kidneys to retain both sodium and fluid (in an attempt to increase blood pressure), which leads to general bloating throughout the body.

Abdominal bloating is due to the increase in progesterone in early pregnancy. Although debated, it is largely believed that progesterone inhibits the ability of the stomach and intestines to contract; therefore they “move” slower and food remains in the GI tract longer, leading to bloating and general discomfort. This "slowness" can also lead to constipation.

Certain medications can cause or worsen bloating/constipation in early pregnancy.

These include medications prescribed to treat nausea and vomiting, antacids for heartburn, and certain multivitamins.

Iron supplements are commonly associated with constipation, the frequency and severity of which depends on the amount of iron released in the stomach. Pregnant women taking iron supplements (for anemia) should consult with their HCP if their constipation becomes too unbearable as there are different options available.

Read more about Constipation/Bloating and pregnancy.

Nausea and Vomiting

Nausea and vomiting are two of the most synonymous symptoms of pregnancy (known formally as Nausea and Vomiting of Pregnancy [NVP], or informally and erroneously as “morning sickness”).

It is currently estimated that up to 90% of pregnant women will experience nausea, vomiting, or both to some degree in early pregnancy; 20% of women may even experience these symptoms before a positive pregnancy test.

On average, the length of time women may experience these symptoms ranges from a few days to a full nine months (very rare), but the average appears to be about 35 to 56 days, or about 5 to 8 weeks. These symptoms tend to go away closer to 14 to 22 weeks of pregnancy rather than the commonly stated 12 weeks.

There are many suspected causes of nausea/vomiting in early pregnancy. It is likely women experience several causes and contributing factors at the same time that dictate the severity and length of their nausea and/or vomiting (fatigue, constipation, bloating, and dizziness contribute to their severity).

Proactive steps may help prevent severe nausea/vomiting in some cases.

Current research indicates there are steps women can take from the very onset of pregnancy (or ideally, before) to potentially prevent severe and prolonged NVP. Learn more.

Learn more about Nausea and Vomiting of Pregnancy and how to manage these symptoms.

Acid Reflux

Acid reflux occurs when stomach acid overflows into the esophagus, resulting in heartburn. In medicine, reflux generally means “in a direction opposite to normal” (i.e. acid traveling back up from the stomach).

Progesterone and relaxin cause a relaxation of the valve/sphincter between the stomach and esophagus. This sphincter helps keep food in the stomach. When it is relaxed, this makes it easier for acid to travel back up the esophagus. This, on top of the possible delay in gastric emptying (and bloating and constipation) can make women experience reflux very early in pregnancy.

Reflux can range from mild to severe as early as the first few weeks. Therefore, it is assessed that reflux can cause, contribute to, or exacerbate nausea, vomiting, and aversions (reflux can make foods taste differently).

Reflux can also cause irritation of the upper esophagus. This irritation may easily trigger the gag reflex, further contributing to gagging and/or vomiting.

Learn more about Acid Reflux and Heartburn and pregnancy.

Reflux, by itself, can cause a feeling of "burning" in the chest/throat as well as a sour taste at the back of the throat.

Skin Changes

Changes in skin pigmentation (called melasma or chloasma) are experienced by up to 90% of pregnant women and is considered one of the earliest signs of pregnancy.

It starts from the first trimester and occurs in areas that are already pigmented such as the nipples, areola, genital areas, around the eyes and eyelids, and the midline of the abdomen, known as the linea nigra.

The linea nigra is a vertical line that typically runs from the pubic bone to the belly button, but can run all the way up to the chest.

It is theorized that estrogen, progesterone, and components of the placenta cause an increase in melanogenesis – the process that produces melanin, a type of dark pigment in the skin (sunlight also causes melanogenesis, resulting in a "tan").

Women may also experience a change in their acne pattern in early pregnancy.

Learn more about Skin Changes and pregnancy.

Frequent Urination

Frequent urination is a well known symptom of pregnancy, especially in the third trimester, as the heavy weight of the uterus and fetus compress the bladder. However, frequent urination also occurs as early as 7 weeks of pregnancy – but for different reasons.

The fast, increasing rise of HCG causes more blood to flow to the kidneys. This, on top of increased blood volume, leads the kidneys to eliminate waste quicker than prior to pregnancy.

The kidneys also experience a rise in glomerular filtration rate (GFR). Glomerular filtration is the initial process in urine production. When GFR increases, so does urine production.

GFR rises as much as 25% by 4 weeks of pregnancy (and 50% by the beginning of the 2nd trimester).

It is common to experience bloating, swelling (fluid), and increased urination at the same time.

The way the pregnant body increases urine production at the same time as it conserves sodium and fluid is completely different than the non-pregnant body and researchers still do not completely understand it (learn more).

Learn more about Urinary Frequency in pregnancy.

Breast Tenderness

Higher levels of estrogen, progesterone, and prolactin in early pregnancy result in structural changes of the breasts.

Under the influence of estrogen in the first trimester, ducts multiply and grow, and alveolar-lobular growth occurs as well.

Breast soreness is a common complaint in all trimesters due to these changes, but is usually most pronounced in the first half of pregnancy. The greatest amount of breast growth usually occurs before 22 weeks.

The increase in blood volume may also cause visible veins on the breasts, even before the occurrence of any physical growth.

Learn more about Breast Changes in pregnancy.

Varicose Veins

The visible veins described above can also occur on other parts of the body, specifically the legs. This occurs not only due to blood volume increase, but also from the decrease in blood pressure. Decreased blood pressure means a slower return of blood to the heart, which more easily collects in the veins of the lower body.

Note: This normally gets worse throughout pregnancy. As the heavy uterus (and fetus) compresses veins in the pelvic area, this slows blood return even further; veins can swell, protrude, and cause discomfort.

Learn more about Varicose Veins and pregnancy.

Back Pain

Many women first experience back pain in the early weeks of pregnancy, when physical changes are not yet a factor.

It is not quite known what causes back pain this early and even hormonal causes are debated. Certain hormone levels (such as relaxin) have not been found to be higher in women experiencing lower back pain than those who are not.

Regardless – joints, ligaments, and tendons start loosening in the first trimester to help the musculoskeletal system prepare and adapt for the growing pregnancy. It is possible this loosening starts to cause back pain even before the uterus adds its own strain.

Due to the above, it is important women call their HCP if they notice early back pain. Since it is likely back pain could increase as pregnancy progresses, learning and implementing early management techniques will be critical in the avoidance of severe pain later in the third trimester. Learn more about Back Pain and pregnancy.

Nasal Congestion

The capillaries in the nose become inflamed early in the first trimester due to blood volume increase and likely – to a lesser degree – hormones.

This extra blood volume swells the nasal capillaries with extra fluid, leading to inflammation.

Exactly how hormones affect nasal congestion and which hormones are responsible is not known, but higher levels of estrogen and/or placental growth hormone have been identified through biopsy results of nasal membranes of pregnant women with congestion.

Learn more about Nasal Congestion and pregnancy.

Hot Flashes/Sweating

Overall, there is very limited information regarding why women may sweat more during early pregnancy. However:

Due to an increase in blood volume, blood is closer to the skin, and therefore warmer, which increases sweating. Sweating is used as a skin-cooling mechanism. "Excess" sweating in early pregnancy could be the body's attempts to protect and better regulate body temperature as excess heat is dangerous during early pregnancy

Additionally, although the body’s sodium and water relationship during pregnancy is not completely understood, pregnant women do retain a significant amount of fluid, and sweating could be a temporary attempt to get rid of excess fluid or achieve a better balance between sodium and/or fluid (as well as body temperature).

Progesterone also raises body temperature, but interestingly, it lowers the rate of sweating. Estrogen has the opposite effect; it is possible that women with more estrogen during pregnancy may be more likely to sweat.

Learn more about Hot Flashes/Sweating and Pregnancy.


Headaches in early pregnancy are common; they are assessed to be triggered by a change in hormones during pregnancy and the body’s attempts to adapt to those fluctuations.

Due to women responding differently to hormones, pregnant women can experience an increase or decrease in their headache pattern, or no change at all. Fortunately, research indicates most women will likely notice their headaches either go away or greatly improve in the second and third trimesters due to a stabilization of hormones.

Headaches can also be caused by the body's reaction to other early symptoms of pregnancy such as:

Learn more about Headaches and pregnancy.

Hunger and Cravings

The early production of human placental lactogen and progesterone increases appetite early in pregnancy; both hormones are well-known appetite stimulants (estrogen decreases appetite).

Ghrelin, known as the “hunger hormone”, stimulates appetite, increases food intake, promotes fat storage, and plays a role in the control of insulin release – all important variables during pregnancy.

Levels of ghrelin increase right before eating and when someone has not eaten in some time (resulting in “hunger pains”).

Ghrelin and its receptors have been identified in the placenta, clearly indicating a role for ghrelin in reproduction. Ghrelin concentration begins to increase right away in the first trimester, peaks at mid-pregnancy, and reduces to the lowest level in the third trimester and after delivery.

Learn more about Hunger and pregnancy.

Learn more about Specific Cravings and pregnancy.

Trouble Sleeping

Most studies suggest there is an increased need for sleep in early pregnancy based on the early metabolic requirements and extreme fatigue described above. Further, high levels of HCG and progesterone promote “sleepiness”. (Conversely, the progesterone drop in late pregnancy may be the reason for women’s sudden energy bursts, or "nesting", near delivery.)

This has been described as a paradox of pregnancy: despite the need for healthy sleep and the body's attempt to promote it, so many other changes and symptoms of pregnancy make achieving adequate rest impossible – most notably, nausea, vomiting, back pain, frequent urination, and hot flashes/sweating.

Learn more about Sleep and pregnancy.


Women need adequate physical, emotional, and mental health support to help set up a healthy pregnancy from the start.

Partners/support should consider learning about these early signs of pregnancy. Early pregnancy/first trimester symptoms can be surprising, overwhelming, and may come on quickly.

When women and their partners/support are working off the same page, women feel more supported, more understood, less frustrated, and have an additional resource they can count on when symptoms get too difficult to manage on their own.

Partners/support can play a role in helping women avoid aversions, get more sleep and rest, manage their nausea/vomiting, and recognize warning signs (below).


It is recommended that women call their HCP as soon as they learn they are pregnant or suspect they may be pregnant; physical symptoms by themselves are not sufficiently reliable to diagnose pregnancy.

Of note, while mild cramping can occur in early pregnancy, women should not experience pain. Pain could be a sign of an unrelated condition or a sign of ectopic pregnancy which is considered a gynecological emergency.

Women should also call their HCP (or seek emergency care) at anytime if they experience significant shortness of breath, extreme fatigue, abdominal pain, chest pain, dizzy spells, changes in their vision, or faintness.

Women should also:

  • Start/continue taking prenatal vitamins that include at least 400 mcg/day of folic acid

  • Maintain overall adequate nutrition and hydration

  • Quit/avoid smoking and secondhand exposure (including e-cigarettes* and marijuana)

  • Quit/avoid recreational drugs

  • Quit/avoid drinking alcohol

  • Call their provider immediately if taking any medications to determine if medication regimen needs to be changed or stopped (women should not stop or start taking any medications until they have spoken with their provider)

  • Learn family medical history for first appointment


A Partner's Guide to Pregnancy (American College of Obstetricians and Gynecologists)

Good Health Before Pregnancy: Prepregnancy Care (American College of Obstetricians and Gynecologists)

Pregnancy (U.S. Centers for Disease Control and Prevention)


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