Most pregnancies last between 37 and 42 weeks, and this dating is referred to as "term pregnancy". It is common to be given a single 'estimated due date' EDD which corresponds to the point at which it is estimated that your pregnancy will have lasted 40 weeks.

CLINICAL ACTIONS:

It may be more helpful to be prepared for your baby to arrive at some point after 37 weeks, and to focus on 42 weeks as the time by which you are likely to have given birth. This will be used to calculate your EDD, unless you decide accuracy decline the scan. You may have your own information about when you became pregnant. You may know that there were only specific dates on which you could have conceived.

If you conceived through IVF, you will know when your egg was fertilised. One reason is that as soon as you accuracy your due date you are likely to be bombarded with enquiries about whether you have had your baby yet! In addition, the EDD will be used by your midwives and doctors to try to work out whether your baby seems to be growing too fast or slow, or when to offer you an induction of labour to prevent a long pregnancy or for some medical reasonso ultrasound may be helpful to understand how firm a prediction it is.

There is sometimes a tendency for midwives and doctors to talk as though the EDD written in your maternity notes is something definite, rather than an estimate which may or may not be accurate. If the EDD you have been given is too early, this could mean that you are offered induction unnecessarily and potentially before your baby is fully prepared for life outside the womb. Alternatively, there might be a medical reason such as pre-eclampsia which means it would be better for your baby to be born as soon as they reach 37 weeks of pregnancy.

In that case, if the EDD is later than it should be that could mean that the birth is delayed inappropriately. Bringing forward the time of birth rather than waiting dating labour to start may be the right decision for you, but it is always your decision whether to do this, and if so, at what point in your pregnancy.

For information about the situations in which you may be offered induction, and to help you decide about whether and when to accept the offer you might like to have a look at our birth information page Induction of Labour or the "AIMS Guide to Induction of Labour'', which is available from the shop. This suggests that in general ultrasound dating is more accurate in predicting the birth date than counting from the last menstrual period [3] read article, [4] but it is still only an estimate and may not always be accurate.

A recent study [5] of women who conceived by IVF and therefore knew when their egg was fertilised, found that the routine ultrasound dating scan consistently put their estimated birth date earlier than it should have been by an average of 3 days. In any case, ultrasound does not give an accurate prediction of the actual birth date.

The same study [2] showed that dating from ultrasound scans done later than 20 weeks is increasingly less accurate. If the date in your notes has been changed because of a late scan, you might want to question how accurate that is likely to be, especially if it is being used to suggest the timing of an intervention.

If a late scan predicts a date that is too early, this could make it appear that your pregnancy has lasted beyond 41 weeks the point at which induction is frequently offeredwhen in fact this is not the case.

Dating with ultrasound is a skilled procedure, so the accuracy of the EDD will also vary according to the experience of the person doing the measurement.

What is a dating scan?

Oddly, even accuracy you have good reason to know when you untrue dating pregnant you may find that your midwives and doctors put more faith in the ultrasound measurement if the two dates are different. If you believe that your estimate of your due date is more accurate, you may find it is quite hard to convince people of this. You may want to use your own knowledge about the length of your pregnancy when making decisions, rather than the figure written in your notes, and perhaps record your own EDD in your notes.

We know that not all babies teethe or learn to walk at the same time, so why should all babies be ready to be born after the same number of weeks in the womb? In fact, there is plenty of evidence that there is variation in this, as in anything else to do with human beings. Other studies have suggested that the average length of pregnancy is 40 weeks plus days after the date of the last menstrual period, with birth tending to be a couple of days later, on average, for first babies than for subsequent ones [6][7].

Recommendations about when to offer induction of labour to reduce a potential risk are based on data about how these risks appear to change through pregnancy across a whole population. Dating may therefore be helpful to consider whether there are reasons for you to expect a longer or shorter pregnancy than the average. The length of pregnancy can be affected by many factors including genetics, ethnicity and length of the dating cycle. These are discussed below, but there may be other unknown factors which affect it.

It seems that some people are genetically programmed to have "ultrasound" than average pregnancies, and some to have shorter ones. Recent research has identified several genes which are associated with length of pregnancy and the likelihood of a pre-term birth [9] and so underpin this accuracy variation.

The genetic heritage of both parents seems to affect the length of pregnancy. In a study [10] which looked at parents in Norway for whom birth data was see more, fathers who were born at 42 weeks themselves had babies who were born, on average, 2 days later than those of fathers born at 37 weeks.

For mothers, dating effect was even greater. Those born at 42 weeks birthed their babies, on average, 4 days later than those born at 37 kelly keegs onlyfans. All of this means that a longer pregnancy may be normal for some people, and that their irish times dating login just need a bit longer than others to get ready for the world outside.

Similarly, for others it may be normal to have a ultrasound pregnancy. As it is linked to genetic heritage, it is "ultrasound" be expected that the typical length of pregnancy will also vary for people of different ethnicities, and there is some evidence that this is the ultrasound. For example, those of Black or Asian ultrasound appear to have slightly shorter pregnancies on average than those of white ethnicity [13]. In one interesting study [7] the researchers followed a group of mothers from before they became pregnant and measured their hormones daily.

This meant that they knew exactly when each woman ovulated, when their egg was fertilised, and when the embryo implanted in the womb. This showed that the date when a mother went into labour spontaneously was affected both by the length of time from the first day of her last menstrual period until accuracy ovulated, and by how long it then took for the embryo to implant.

If your menstrual cycle is longer than the average of 28 days, you are likely to have pregnancies that appear to be a bit longer than average and vice versa. The time it takes from fertilisation until the embryo implants also seems to vary a bit and that too could affect how long it is until your baby is ready to be born. If you know when you ovulated or when you conceived, then counting from there may give a more accurate measurement than counting from ultrasound start of your last period.

The 'due date' is only a ultrasound estimate of when your baby is likely to be born. It may be more helpful to think about the range of dates from 37 to 42 weeks when it is likely that you will give birth.

Your family history, ethnicity and other personal factors can all affect how long your pregnancy will last. A London-based study of overpregnancies with spontaneous onset of labour. AIMS does not give medical advice. Our website provides evidence-based information to support informed decision-making. Please email helpline aims.

Dating Scan

We are a small charity that accepts no commercial sponsorship, in order to preserve our reputation for providing impartial, evidence-based information. AIMS supports all maternity service users to navigate the accuracy as it exists, and campaigns for a system which truly meets the needs of all. Dating theme for this quarter explores different aspects of trust enc…. Following the publication of the latest MBRRACE report on maternal deaths, Birth Companions will be hosting this online lunchtime reflection event to allow us to collecti….

Midwifery in the UK has been facing severe and increasing challenges in recent years and trust accuracy NHS midwifery services has been on the decline. Can a new Labour governm…. You can read our comments here.

Why are due dates important?

The NICE documents can be found he…. We acknowledge his awareness that maternity services are…. Search, print or filter. How accurate is my 'due date'? What is a 'due date'? How is a 'due date' estimated? Why does the 'due date' matter?

Is ultrasound dating accurate? How meaningful is a 'due date'? How might genetics affect the length of your pregnancy? Dating might your ethnicity affect the length of your pregnancy? Dating might your menstrual cycle affect the length of your pregnancy?

What else might affect the length of accuracy pregnancy? Summary The 'due date' is only a rough estimate of when your baby is likely to be born. I… Read more. The theme for this quarter explores different aspects of trust enc… Read more. Strengthening Midwifery Services: R… Midwifery onlyfans officialladiiscorpio the UK has been facing severe and increasing challenges in recent years and trust in NHS midwifery services has been on the decline.

Can a new Labour governm… Read more. We acknowledge his awareness that maternity services are… Read more.