Video: How do you calculate a due date?

Playlist: Early Pregnancy Q&A

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How do you calculate a due date?

Dr Sarah Jarvis MBE, FRCGP

00:48

How do you calculate a due date?

Dr. Sarah Jarvis MBE, FRCGP

03:17

What pregnancy screening tests are available?

Dr. Shazia Malik, MRCOG

01:58

What are the different stages of pregnancy?

Dr. Sarah Jarvis MBE, FRCGP

01:43

How does a baby develop in the womb?

Dr. Sarah Jarvis MBE, FRCGP

00:58

What are the early signs of pregnancy?

Dr. Sarah Jarvis MBE, FRCGP

00:53

How long does it take to get symptoms of pregnancy?

Dr. Sarah Jarvis MBE, FRCGP

00:44

Can you have pregnancy symptoms before your missed period?

Dr. Sarah Jarvis MBE, FRCGP

01:00

What can cause the same symptoms of pregnancy?

Dr. Sarah Jarvis MBE, FRCGP

How do you calculate a due date?

Dr Sarah Jarvis

When you calculate your due date, you start with the first day of your last period - assuming you know when that was. While calculating due dates, we assume that every woman has a 28-day cycle, so when you have an ultrasound scan it may turn out that your due date is little bit different.

Your ultrasound scan is usually accurate to within about a week. But if you have a 28-day cycle and you know the first day of your last period - all you have to do is work out 40 weeks from there. Now for most months of the year, that’s simply nine months plus one week. However this cycle of months does not include February. In other words if you get pregnant in March, April, or most of May then it’s not quite so accurate because February is a shorter month.

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What pregnancy screening tests are available?

Dr Shazia Malik

When you are pregnant, your doctor or midwife will offer you tests that can check whether your baby is developing as expected, or if there are any signs your baby has a condition, such as Down's syndrome. These tests occur at different stages of pregnancy. The first test occurs when you are around 12 weeks pregnant. This involves a blood test and specialist ultrasound scan, which are then combined to give you an idea of whether you have a high or low chance of your baby having Down's syndrome or any other chromosomal anomaly.

The ultrasound and the blood test will also check for any physical anomalies in your developing baby - for example, spina bifida - and this can also be picked up at this stage. All these tests are optional and you may choose to have, none, some or all of them. Before you make a decision you - with your partner or fellow parent if they are involved - should have a detailed discussion with your health care team so that you can make the best decision.

If the test does come back as high chance, the only way to know for certain will be further detailed test, such as an amniocentesis test, which will be offered to you by your team. Amniocentesis is where a needle is put inside your womb, fluid is taken from around the baby and the cells from the skin that are in the fluid is sent to the lab to check the chromosomes. From that, we can tell for certain whether your baby has Down's syndrome or another chromosomal anomaly. There is a small risk of miscarriage with this procedure. This will be discussed with you by your doctor before you decide whether you want to have the test or not.

You will have another ultrasound scan at around 20 weeks of pregnancy. This scan is to do a detailed assessment of the internal organs of your baby. By this time, your baby is much bigger and your womb will be around the level of your tummy button. The person performing the ultrasound scan will have a detailed look into your baby’s heart, brain and internal organs. It’s a very important scan as anomalies can be picked up at this stage.

Further on in your pregnancy, you may be offered another ultrasound scan if there is any concern that the baby is not developing as expected in terms of size. This checks whether the placenta is working well, and to check the size of your baby is what is expected for you at your stage of pregnancy. The scan will also determine whether the fluid around the baby is at a normal level and that the placenta is not low lying. Of course, at any other stage of pregnancy your team will offer you further tests as required.

What are the different stages of pregnancy?

Dr Sarah Jarvis

We tend to divide pregnancy into 3 month chunks - known as trimesters - and there are three of them. In the first three months, most people around you won’t know you are pregnant but you most likely will. You often feel very tired. You may feel sick and you may experience some other symptoms, such as breast tenderness or needing to wee more often. A lot of development is going on in your baby at that time. By 3 months of age, your baby is only about the size of pea pod - but you will be able to see the baby’s heart in the ultrasound scan.

The second trimester of pregnancy occurs from 13 to 26 or 27 weeks of pregnancy. Your sickness and nausea may become less severe and your energy levels may return to normal. The risk of miscarriage is dramatically dropped and your baby is often likely to start moving. You can usually feel your baby moving at between 17 and 18 weeks of pregnancy.

In the third three month period - the last trimester - most of your baby’s development has happened already, it’s just the question of maturing the bits that are already there. Your baby is getting bigger and this is why you really start to notice yourself slowing down. You may find that the baby is pushing on your diaphragm so that you are getting more short of breath or pushing down below so you need to wee very often. You will often find it difficult to sleep. You may find your legs and ankles getting swollen and you are likely to find yourself getting much more tired. However, your baby is developing nicely - and unaware of all the discomfort you are going through - and by nine months, should be due to be born.

How does a baby develop in the womb?

Dr Sarah Jarvis

An extraordinary amount of development goes on in the first three months of your pregnancy. For about six weeks after your last period, you’ll already be able to see your baby’s heart on an ultrasound scan. By two months, your baby is about the size of a kidney bean and has got limb buds or little webbed fingers that you can just about see. By three months, their back bone is pretty much fully developed, which is why it's so important to take folic acid in the first three months of pregnancy to reduce the risk of the back bone problem spina bifida.

By four months, their skeleton is forming well and bones have started to be visible on the scan. By six months, your baby is about one and half pounds in size. Their hair is continuing to grow. They are beginning to fill out and their eyes are developing.

By seven months, they are opening and closing their eyelids. By eight months, your baby’s lungs are about to develop so they can breathe in the outside world without problems. At 36 weeks, your baby is considered fully grown, or full term.

What are the early signs of pregnancy?

Dr Sarah Jarvis

The obvious first sign of pregnancy that most woman think of is missing a period but you can also get spotting. Implantation bleeding is thought to happen when the fertilised egg attaches to the lining of the uterus. If you get light bleeding with tummy pain, it could be an ectopic pregnancy or pregnancy outside the womb, so it's important to be aware of that. Feeling sick and being sick are very common, as is feeling really tired. It’s amazing how much change is going on in your body.

Most of the organ development happens in those first twelve weeks. Your breasts may feel swollen and tender. You may find that you need to wee more often and you often find that your sense of taste changes. This could be connected with morning sickness. There are other things that could cause the same symptoms as pregnancy so the best way to be certain is to do a pregnancy test.

How long does it take to get symptoms of pregnancy?

Dr Sarah Jarvis

When you miss the first day of your period, it’s usually about four weeks since the first day of your last period. That's when your pregnancy will be counted from by your doctors and midwives. However, that’s actually only two weeks since your egg was fertilised by that sperm.

It’s around about four weeks from the first day of your last period that you tend to get a missed period and start to get early symptoms such as feeling tired, feeling sick, feeling need to wee more often and sometimes breast swelling and tenderness. A few women get symptoms before that, and some women don’t get symptoms until later on. But you are more likely to get symptoms early - and more severe symptoms - if you have a multiple pregnancy, in other words, twins or more.

Can you have pregnancy symptoms before your missed period?

Dr Sarah Jarvis

We count your weeks of pregnancy from the first day of your last period but in fact your egg meets that sperm which is going to fertilise it about two weeks after the first day of your last period. So, by the time you miss your first period, your sperm and egg have been together for just two weeks.

That’s quite early to be having symptoms, although, some women can get symptoms like feeling sick or being sick, breast swelling, tenderness, needing to wee more and feeling tired. Those symptoms are more likely if you hormones levels are very high.

What can cause the same symptoms of pregnancy?

Dr Sarah Jarvis

The early symptoms of pregnancy are often quite vague. Missed periods, stress, excess exercise, all the years running up to the menopause can all cause your periods to become irregular or to stop happening. The condition of polycystic ovaries could also be to blame.

Feeling sick could just be due to a stomach bug. Feeling tired could be due to either a bug or something like anaemia - where your iron levels are too low. There are lots of causes of tiredness.

Coming up to the menopause, you may find that your periods become less regular and then stop completely. So, please don’t assume that it is the menopause before you’ve checked if you’re pregnant. And if your breasts are swollen and tender, that could indicate pregnancy. But it could be pre-menstrual fluid retention or possibly an infection in your breast. Therefore, it is best to do a pregnancy test and if you are concerned about any symptoms, see your doctor.