PMS, also known as Premenstrual Syndrome, occurs in the days or weeks leading up to the menstrual period. While up to 75% of people with periods experience PMS symptoms, PMS is clinically defined as a range of physical, psychological, and behavioural symptoms that occur in the luteal phase of the menstrual cycle (the two weeks before your period). These symptoms disrupt the way we normally function and interfere with our daily lives, work, school, or relationships. Symptoms typically resolve a few days after we get our period.

Physical symptoms include abdominal cramps, bloating, swollen or tender breasts, headaches or backache, constipation or diarrhoea, fatigue, and clumsiness. People with PMS may also notice changes to their skin, including being oily or more prone to acne, or find that their hair can be greasier. Psychological symptoms include feelings of anxiety, sadness, depression or irritability. You might also experience behavioural symptoms, like mood swings, brain fog (trouble remembering things), feeling very tired or struggling to sleep.

We don’t fully understand why PMS occurs, but it might be due to fluctuations in the levels of female hormones during the luteal phase, or our relative sensitivity to such. Premenstrual symptoms typically occur in the two weeks before our period begins (aka, the luteal phase). At the beginning of this phase, progesterone levels are high, and across the duration of the two weeks, both progesterone and oestrogen levels decrease until menstruation begins.

‘Early pregnancy’ can be a bit of a confusing term, especially when it comes to calculating the number of weeks pregnant you might be. This is because the number of weeks is actually calculated from the first day of your most recent period (so, in reality, you’re typically not actually pregnant for the first two, as the body prepares for ovulation). Once the egg has been released and fertilised by sperm, an egg then implants in the uterus lining.

Once implanted, cells begin to grow that will eventually form part of the placenta. These start producing hCG (human chorionic gonadotropin), which is the hormone detected by pregnancy tests. During the following weeks, you may begin to notice some signs of early pregnancy.

There are many perceived overlaps between the symptoms of PMS and the presentation of pregnancy. This is likely because of high levels of hormones experienced during the luteal phase of the menstrual cycle (when a person is not pregnant), and implantation/early stages of pregnancy (when a person is pregnant). If we’re not pregnant, our progesterone and oestrogen levels drop and we get our period. If we are pregnant, those hormone levels remain high and the embryo begins to develop. Because scientists believe that one of the main reasons we get PMS symptoms is because of a sensitivity to progesterone, high levels of this hormone during the luteal phase and pregnancy can trigger the same symptoms, regardless of whether the cause is a regular cycle or a pregnancy. 

Another theory for the cause of PMS is an imbalance of progesterone and oestrogen. In pregnancy, we generally have high levels of oestrogen to balance out the higher progesterone levels, which is not the case in PMS. Therefore, we theoretically can’t get PMS whilst pregnant, but may experience many similar symptoms. These are outlined below.

There are many symptoms that could be a sign of PMS or early pregnancy. We’ve included a list of the most common PMS symptoms below, and whether you might experience them in early pregnancy too. For a quick-fire check on which you might be experiencing, try our pms symptoms vs pregnancy symptoms quiz.

Mood swings: both. We can experience a change in mood, emotion, and our perceived capacity to cope with stressful situations during PMS and pregnancy. 

Pain and cramping: unfortunately, both. However, where we feel the pain might vary between PMS and pregnancy.

Spotting: both. In the first few weeks of pregnancy, you may experience what’s known as implantation bleeding, this is also known as spotting. Of course, if we’re about to get our period, we can experience this too.  

Appetite changes: both. Just before our period and during early pregnancy, the foods we crave can change. However, how these changes present is different between PMS and pregnancy. 

Breast tenderness/swelling: both. 

Increased urination: both (who knew!). 

Bowel changes: both PMS and pregnancy. 

Fatigue/disrupted sleep: yep, you guessed it, both.

If you start to feel sick or nauseous, this is typically a sign of pregnancy. This sign usually starts appearing around four to six weeks post-implantation, and it’s typically referred to as morning sickness (although it can actually happen at any time of day or night). You shouldn’t feel sick or nauseous during PMS, though, so if you do, contact a healthcare professional.

Mood: during PMS, the grouchy and irritable feelings are likely to go away once menstruation starts. In pregnancy, the mood changes can last until you give birth.

Pain: oestrogen levels are low at the end of the luteal phase, which can lead to ‘menstrual headaches’. This is because oestrogen is thought to have a pain-regulating effect, and low levels of such mean we’re more sensitive to pain. Interestingly, headaches can also occur in the first trimester but are most likely a result of high oestrogen levels and increased blood volume. When it comes to joint and lower back pain, this is most likely a sign of PMS, as these two symptoms typically won’t present in the first trimester of pregnancy. However, they may crop up during the later stages when the baby is larger and weighs more. 

Cramps: during PMS you might experience cramping in your lower abdomen a day or two before your period. We can usually feel them in the lower abdomen area and are sometimes accompanied by backache. The pain usually decreases during our period and eventually disappears by the end of our flow (~5-7 days in total). But how are early pregnancy cramps different from PMS cramps? In early pregnancy, you may experience mild or light cramping like the cramps you get before/during your period, and they’ll also be in the same area. Light pregnancy cramps usually last for weeks or months (so, longer than PMS cramps) but if they are accompanied by bleeding, see a doctor immediately as this could be a sign of miscarriage. 

Changes in appetite: just before our period, progesterone and oestrogen drop. For people with PMS/PMDD, serotonin levels can drop too. At the same time, our cortisol (the stress hormone) levels rise. This combination leads to cravings for sugary foods, such as chocolate. Changes in appetite can also be a sign of early pregnancy. This may be due to changes in hormone levels that alter your sense of smell and taste. 

Urination: 42% of women who experienced changes in their urination said this was worse before their period. This is thought to be because of elevated levels of progesterone, which has an adverse effect on the female lower urinary tract function. In the first trimester of pregnancy, you may need to urinate more, too. This is also likely due to increased levels of progesterone (and hCG) which can lead to feelings of urgency. However, in both PMS and pregnancy,  if you find you’re needing to wee more and this is accompanied by pain, peeing at nighttime, or blood in your urine, this can be a sign of a UTI and you should seek medical advice, especially in pregnancy.

Bowel changes: progesterone can cause digestive disturbances including constipation. Because levels of this hormone rise during the luteal phase of the menstrual cycle and pregnancy, constipation can occur and present in the same way in both PMS and pregnancy. However, as the levels of progesterone drop just before we get our period, these symptoms should ease a few days into our cycle. With pregnancy, they can last a little longer. 

Fatigue and tiredness: these are common in both PMS and pregnancy, as is trouble sleeping. Like many other symptoms, these symptoms subside once your period starts, but in pregnancy, the increased progesterone can make those tired feelings more pronounced, particularly during your first trimester. Exhaustingly, fatigue and tiredness can last throughout your pregnancy.

There are many treatments for PMS. These range from lifestyle changes to antidepressants. Because PMS is such a personal experience, so is the effectiveness of each solution. What works for some people won’t work for others. For a rundown of the currently recommended treatments, read our articles on medicinal treatments, alternative therapies, supplements, and lifestyle adjustments. Please note, not all PMS treatments are suitable for people who are pregnant, so speak to a healthcare professional before making any changes to your routine, diet, supplement regime, or medication.

Heat packs can help ease back and joint pain, as can a warm bath. Pregnancy support belts or slings can also help reduce pressure on your pelvis and back by supporting your bump. Some people find specially-shaped pillows help reduce pressure whilst they sleep. When it comes to our breasts changing shape, size and weight during pregnancy, it’s important to make sure you’re wearing a bra that fully supports you and is the correct size. Increasing your dietary fibre intake can help with constipation, as can regular exercise. For disrupted or lack of sleep, if possible allow yourself an afternoon or mid-morning nap, or get an early night a few times per week. Warm baths before bed and short sessions of mindfulness and meditation may also help you sleep.

Despite the symptoms of PMS and early pregnancy being very similar, people who experience PMS generally find that their symptoms improve during pregnancy. This is because, unlike in the luteal phase where progesterone levels are high and oestrogen levels are falling, during pregnancy both these hormones remain at high levels. It’s thought that this more ‘balanced’ state of hormones reduces the impact of high progesterone levels. 

However, after pregnancy, people with a history of PMS/PMDD are almost twice as likely to suffer from postpartum depression than those who don’t. This may be due to the increased sensitivity of people with PMS/PMDD to hormone fluctuations, or the abrupt decrease in hormone levels experienced after giving birth and the effect oestrogen has on serotonin (the happy hormone) production.