Pregnancy is not likely to bring on asthma if you didn’t previously have it, but its effect on women who do have asthma is unpredictable.
Around one-third of asthmatic women will see an improvement; one-third will see no change and one-third will find their symptoms get worse.
The best way to ensure a healthy pregnancy is to keep your asthma well-controlled. As soon as you find out you're pregnant, see your GP for advice on how to manage your asthma.
Find out more about asthma and pregnancy, including taking your medication.
Around 8 in 1,000 babies are born with something wrong with their heart. This can sometimes be called a cardiac abnormality, congenital heart disease or congenital heart defect.
Most of these babies survive and grow to adulthood, and may go on to have children themselves.
If you were born with a cardiac abnormality and have had a successful operation to correct it, this does not mean you're completely cured. You'll probably have some scarring of the heart, and this may make you more prone to infections or an irregular heartbeat.
Many women with congenital heart disease have a successful pregnancy, but pregnancy puts your heart under significant strain. This can lead to problems, so talk to your doctor before you get pregnant or as soon as you know you're pregnant.
Coronary heart disease (CHD) is when your arteries get narrower due to a build-up of fatty deposits inside them. This restricts the flow of blood and can lead to chest pain, called angina, or a heart attack.
Your heart needs to work harder in pregnancy so, if you've got heart disease, it's important to get the right care and support.
Some women develop heart problems for the first time in pregnancy.
During your pregnancy, you should be under the care of a consultant obstetrician and a cardiologist in a hospital maternity unit.
You can expect to have more frequent antenatal check-ups, particularly if your CHD is related to other conditions, such as diabetes or high blood pressure.
Make sure you attend all your appointments or reschedule them if you have to cancel.
If you already have type 1 or type 2 diabetes, you may be at higher risk of having a large baby (which increases the risk of a difficult birth), having your labour induced, having a caesarean section, having a baby with an abnormality, and having a miscarriage or stillbirth.
The best way to reduce the risk to your own and your baby's health is to make sure that your diabetes is well controlled before you become pregnant.
Ask your GP or diabetologist (diabetes specialist) for advice. You may be referred to a diabetic pre-conception clinic for support.
Find out more about diabetes and preganancy.
It's hard to predict how pregnancy will affect epilepsy. For some women, their epilepsy is unaffected, while others may see an improvement in their seizures. But as pregnancy can cause physical and emotional stress, seizures may become more frequent and severe.
If you're taking drugs to control your epilepsy, it's recommended that you take a high (5mg) daily dose of folic acid as soon as you start trying for a baby. Your GP can prescribe this.
If you become pregnant unexpectedly and have not been taking folic acid, start taking it straight away.
Whatever you do, don't alter or stop taking your epilepsy treatment without specialist medical advice. A severe seizure during pregnancy could be fatal for you and the baby.
Find out more about epilepsy and pregnancy.
If you have high blood pressure, or hypertension, your heart has to work harder to pump the blood around your body. This can affect the heart muscle.
While the type of treatment you are given will depend on the cause of your high blood pressure, the key to a healthy pregnancy is to ensure that your blood pressure remains under control. Having check-ups with your antenatal team is the best way to monitor your condition.
Find out more about high blood pressure and pregnancy.
Mental illness can progress more rapidly during pregnancy. If you stop taking prescribed medication without consulting your doctor when you become pregnant, this can make your illness return or become worse.
When you have your first antenatal appointment you should be asked if you have ever had problems with your mental health in the past.
You should also be asked about this again following the birth of your baby. This is to allow your care team to pick up on any warning signs more quickly and to plan appropriate care for you.
Find out more about mental health problems and pregnancy.
Obesity, which is usually defined as having a body mass index (BMI) of more than 30, is increasingly common. Around 15-20% of pregnant women are now obese.
Being obese in pregnancy increases your risk of complications, such as gestational diabetes, pre-eclampsia, miscarriage, stillbirth and needing a caesarean section.
Before you get pregnant you can use the BMI healthy weight calculator to work out your BMI. But once you're pregnant this may not be accurate, so consult your midwife or doctor instead.
Most pregnancies of obese women are successful, but possible problems for your baby can include premature birth and a higher risk of obesity in later life.
Find out more about obesity and pregnancy.