If problems occur you may be advised that delivering your baby earlier is the safest option.

For advice on recognising signs that you are going into labour, or for information on some types of pain relief in labour, follow the links.

But ultrasounds can also lift the lid on a few worries you might be having. The main reason for the ultrasound is to work out how many weeks pregnant you are, and to estimate your due date.

The length of your pregnancy is calculated from the first day of your last menstrual period (LMP), even though you don't actually conceive until 14 days after your LMP, and later than this if your cycle is longer than 28 days.

Instead, you will be offered a nuchal translucency ultrasound.

This measures a collection of fluid under the skin at the back of a baby's neck. Nearly all ultrasound after 10 weeks can be done through your tummy, and most units ask you to come with a full bladder.

Please remember that the result will not necessarily be the day that your baby arrives.

The actual date may be any time from 38 to 42 weeks in most pregnancies.

It's helpful to know about twins early on, as it's easier to see whether or not they share a placenta.

Finding out about having twins early in pregnancy also gives you more time to prepare for the birth and for your doctor or midwife to plan your care.

It will tell you exactly how many weeks pregnant you are. This measurement, known as the crown rump length, is very accurate in the first trimester. National Institute for Health and Clinical Excellence, clinical guideline 62.

After 13 weeks your baby can curl up and stretch out, so measuring the length becomes less accurate. A randomized trial of prenatal ultrasonographic screening: impact on maternal management and outcome. Antenatal care: Routine care for the healthy pregnant woman.

This pregnancy due date calculator will give you a rough idea of when your baby should be born.