Fertility and pregnancy during perimenopause 

Menopause is a natural stage of ageing where menstruation (having periods) has stopped for 12 months. Perimenopause refers to the transition between having regular periods and menopause. During perimenopause, periods become irregular and ovulation doesn’t always occur every month. It is possible to become pregnant during perimenopause; however, your fertility is reduced. 

Here we will look at how perimenopause reduces fertility, how fertility is tested, how to increase your chances of pregnancy during perimenopause and the risks of pregnancy during perimenopause. 

Why perimenopause reduces fertility

Female babies are born with a fixed number of immature eggs in their ovaries. Each egg is found inside a fluid-filled sac called a follicle. When a female baby grows up and reaches puberty, they will start to have monthly periods. At this point, there are usually 300,000–400,000 eggs.

Every month, a group of follicles, usually around 15–20, start to prepare to release an egg. Eventually, one of these follicles releases an egg and the rest of the follicles in the group die. Up to around 1,000 other follicles are additionally lost each month due to natural cell death. 

Consequently, over time, the number of eggs in the ovaries reduces. The remaining eggs also reduce in quality over time. Although there are repair mechanisms to keep the eggs healthy, these mechanisms start to fail as you age.

During perimenopause, it, therefore, becomes less and less likely that an egg will be released every month, which reduces the chances of fertilisation during sexual intercourse or intrauterine insemination (a type of fertility treatment where sperm is inserted into the womb). 

Poor egg quality also makes it less likely that a released egg will be successfully fertilised or implanted into the womb, which both prevent pregnancy. 

Chances of pregnancy during perimenopause

Perimenopause usually starts in those aged 40–44; however, it can begin earlier. Once perimenopause starts, your chances of becoming pregnant decrease significantly. 

In general, fertility rates decline from around age 35 onwards. Relative fertility rate is a measure of your chances of becoming pregnant at a given age. From age 20–30, the average relative fertility rate is around one, indicating high fertility and a good chance of pregnancy. This drops to 0.6% at age 35 and drops further to 0.1% at age 40. 

Although your fertility decreases with age, if you are going through perimenopause and do not want to become pregnant, you still need to use contraception. Hormone replacement therapy (HRT) is not a form of contraception. 

How to test your fertility

There are many different fertility tests; however, the two most common tests are a blood test for anti-Müllerian hormone (AMH) and an ultrasound scan of the ovaries to count the number of follicles (antral follicle count). 

These measure your ovarian reserve which indicates the amount of eggs you have remaining in your ovaries. If your ovarian reserve is low, your doctor may recommend fertility treatment in the form of in vitro fertilisation (IVF) using your own eggs or using an egg donor. 

How to improve your fertility 

There is no way to increase your ovarian reserve ie the number of healthy eggs you have. However, you can take steps to improve your chances of a pregnancy by following a healthy lifestyle. 

This includes quitting smoking, reducing the amount of alcohol you drink, sticking to a healthy, balanced diet, exercising regularly and managing your stress levels. 

Whatever your age, if you are trying to become pregnant, you should also take folic acid to reduce the risk of certain birth defects. You can also take pre-pregnancy vitamins, including vitamin D. 

Risks of pregnancy during perimenopause

Risks to the baby

The older you are when you become pregnant, the higher the risk of your baby having a genetic condition caused by abnormalities in genetic material called chromosomes. 

You may be offered non-invasive prenatal testing (NIPT) to screen for Down syndrome, Edwards syndrome and Patau syndrome. Further testing, including amniocentesis, may be recommended. 

Amniocentesis is an invasive test to check for genetic abnormalities in the baby during pregnancy. It involves collecting a sample of fluid from the amniotic sac in which your baby is growing. As with any procedure, there are risks; amniocentesis comes with a small risk of miscarriage. 

Pregnancy at an older age also comes with a higher risk of miscarriage, ectopic pregnancy and stillbirth. Stillbirth refers to the death of a baby after completing 24 weeks of pregnancy, while miscarriage refers to the death of a baby prior to 24 weeks of pregnancy. Ectopic pregnancy refers to the implantation of a fertilised egg outside of the womb, such as in a fallopian tube.

Risks to the mother

Pregnancy at an older age increases your risk of worsening pre-existing medical conditions, including diabetes and high blood pressure (hypertension). 

There is a higher likelihood of developing hypertension in pregnancy (preeclampsia). This consequently increases the risk of placental abruption, where your placenta separates early from your womb, and placenta previa, where your placenta sits in the lower part of your womb and fully or partly covers the entrance to your womb (cervix). 

Furthermore, there is a higher chance of having a larger baby, which can be linked to gestational diabetes, but also a higher chance of having a low-weight baby due to restricted growth. 

Due to these higher risks, greater monitoring of pregnancy is needed including serial scans to monitor the baby’s growth. If you are older than 35 you are more likely to have twins or multiple pregnancies, which come with greater risks. 

Interventions for the delivery of your baby are also more likely eg induction labour or a C-section.