Pregnancy and the menstrual cycle

What happens to your menstrual cycle during pregnancy?

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29 January 2022

An introduction to pregnancy and the menstrual cycle

You might be wondering what happens to your menstrual cycle when you fall pregnant. For most women their periods stop, but for some, they continue to bleed throughout the pregnancy. I discuss why this can happen and what’s going on with your hormones during this time.

Some women can have irregular or missed periods and then wonder if they are pregnant. Although missing a period is often an indication that you are indeed pregnant, this isn’t always the case and it can mean something else is going on.

I talk about some of the symptoms of pregnancy compared to those of normal menstrual periods, I describe what goes on with your menstrual cycle during pregnancy and how you can influence your chances of falling pregnant.

What are the signs of being pregnant vs. symptoms of menstrual periods?

So, how do you know if you are pregnant or it’s just another regular month? You might assume it’s obvious, but actually it can be confusing! Many of the symptoms of pregnancy are so similar to those of your monthly period, for women who have symptoms of PMS, it can be especially hard to tell!

Some common symptoms of both include:

  • Stomach cramps – Many women have painful periods and cramp is one of the most common symptoms of menstrual periods.  It has been reported that some women can experience very light cramping early on in pregnancy. This is thought to be due to changes in the womb and fluctuating hormones
  • Tender breastsTender breasts are common in the luteal phase of the menstrual cycle as progesterone levels are at their highest. If you fall pregnant, the levels of this hormone stay high in order to support the womb and sore breasts are therefore common in pregnancy
  • Having low levels of energy – Women can feel low in energy in the lead up to their period, this is partly due to high levels of progesterone relative to oestrogen. In the first few weeks of pregnancy progesterone levels stay fairly high in order to support the womb for carrying your baby. During the first trimester your body undergoes massive changes throughout many different systems and this can contribute to you feeling very tired too
  • Sweating – Increasing levels of hormones such as progesterone can make you feel warmer and sweatier. For example, when you ovulate, your body temperature increases very slightly as a result of a progesterone spike. After conception progesterone continues to rise and this can make you feel warmer and more uncomfortable
  • Feeling nauseousNausea shouldn’t be a regular monthly symptom, perhaps more likely if you suffer from PMS. However, this is a common sign of early pregnancy. ‘Morning sickness’ (although the nausea or vomiting can happen at any time) occurs in up to 80% of women during the first three months of pregnancy and is thought to be due to rising levels of the hormone Human chorionic gonadotropin (hCH).

Although many of these symptoms can be very similar, look out for sudden changes in symptoms from what you are used to month to month. Also, having missed a period is often the symptom that differentiates your normal monthly symptoms and being pregnant.

However, despite this, missing a period still isn’t a sure sign you are pregnant, plus many women have irregular periods so knowing when you’ve actually missed one can also be hard to pin point! It’s best to take a pregnancy test if you suspect you are pregnant.

What happens to your menstrual cycle when you are pregnant?

A commonly asked question is if you can still have your period when you’re pregnant. Technically the answer is no... But, you can experience some bleeding which can be easily mistaken for your period, but technically you aren’t menstruating.

When you become pregnant, your hormones no longer follow the same pattern as they previously did each month. Instead your hormones are in whole new cycle: a one-off, 9 month cycle, that is!

From when you fall pregnant levels of hCH dramatically increase, they peak at around 12 weeks and then drop to lower level for the remainder of the pregnancy. From the time of conception, oestrogen and progesterone levels continue to rise. They get higher and higher, and only decrease after the birth of your baby.

Although you don’t have your period, there may be others reasons for losing blood during your pregnancy. Generally you should always get this checked out but there are some possible explanations:

  • Implantation bleed – In anticipation of your egg become fertilized and implanting in the wall of your womb, the lining of your uterus thickens and becomes a spongy mass of tissue and blood vessels. You may have a small bleed as the egg implants as it disturbs some of this tissue. If you have regular periods this will normally happen approximately a week before your menstrual period would be due
  • Hormone related bleeds – Early pregnancy especially sees big fluctuations in hormones and this can sometimes give rise to bleeding. If the implantation of your egg occurs very close to the time your period would be due, you might still lose a small amount of blood. If your progesterone levels are quite low you may also experience ‘breakthrough’ bleeding where small, looser sections of the lining of your womb are shed
  • A problem with your placenta – Sometimes the growing placenta can incur bleeding, this often resolves itself over time and is more common in the first few months of the pregnancy
  • Cervical bleeding – Your cervix can become more sensitive, after having sex for example. If this becomes apparent, it should be avoided in future as much as possible.

It is advised that you contact your doctor or midwife immediately if you start bleeding and suspect you are pregnant.

Can you become pregnant during your period?

Another common question is if you can still fall pregnant while you are on your period. The answer is yes. This is more common if you have, shorter cycles (more frequent periods) or irregular periods.

Shorter cycles mean everything happens closer together. Since sperm can survive for up to five days inside the vagina, having sex at the end of your period and ovulating quite soon after, could result in you falling pregnant.

How can you increase your chances of becoming pregnant?

If you want to become pregnant tuning into your menstrual cycle and understanding what’s going on in your body can really help you. Here are my top tips:

  • Get to know your cycle and when ovulation is likely to occur – Keeping track of your menstrual cycle is always a good thing. It not only prepares you for your period appearing (or not!) but it also means you can figure out when you are likely to ovulate. You generally ovulate in the middle of your cycle, so, if you have a 28 day cycle you’ll ovulate around day 14. Day 1 of your cycle is the first day of you period. Try keeping a diary for a few months so you can calculate the length of your cycle. You can also buy an ovulation test which can be more accurate. Take note of any symptoms you experience around the time of your period too as this could signal a hormone imbalance. A hormone imbalance could affect ovulation and your chances of falling pregnant
  • Have sex – OK so this might seem obvious, but actually, having sex at the right time and the right amount can help too. Sperm can survive in the vagina for 3-5 days on average, but the female egg can only last for one after being released. Also, taking into consideration how far the sperm have to travel is important. It’s quite a distance from the vagina to the end of the fallopian tubes where the egg starts its journey, therefore it’s actually thought to be better to give the sperm a head start and have sex 1-2 days before ovulation. Also, having sex too often may be detrimental as it could affect the quality of the sperm. Have sex every second to third day rather than every day around your most fertile time could be more beneficial
  • Diet and lifestyle – Diet and lifestyle is really important and has a big influence on your chances of falling pregnant. Ensuring you have a diet rich in essential vitamins and minerals is important – did you know that zinc, for example, is important for healthy sperm in males? The easiest way to achieve a nutrient-rich diet is to eat fresh. It is also important to take a folic acid supplement if you are trying for a baby and continue to eat fresh ingredients if you do fall pregnant. Lifestyle factors are important too; smoking, consuming alcohol and being too stressed can all affect your chances of falling pregnant too. Good luck!


First published in 2016, updated in January 2022.

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