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All pregnant women in England are offered an ultrasound scan at around 8 to 14 weeks of pregnancy. This is called the dating scan. It's used to see how far along in your pregnancy you are and check your baby's development, how does a dating scan work. Your midwife or doctor will book you a dating scan appointment. It will usually take place at your local hospital ultrasound department. The person performing the scan is called a sonographer. You may need to have a full bladder for this scan, as this makes the ultrasound image clearer.

You can ask your midwife or doctor before the scan if this is the case. Find out more about what happens during a pregnancy ultrasound scan. Some abnormalities may also be detected at this scan, such as neural tube defects spina bifida is a type of neural tube defect. Screening for Down's syndrome will happen at the dating scan if:. The screening test for Down's syndrome used at this stage of pregnancy is called the "combined test". It involves a blood test and measuring the fluid at the back of the baby's neck nuchal translucency with an ultrasound scan.

This is sometimes called a nuchal translucency scan. The nuchal translucency measurement can be taken during the dating scan. Find out more about the combined screening test for Down's syndrome. You won't be offered the combined screening test if your dating scan happens after 14 weeks. Instead, you will be offered another blood test between 14 and 20 weeks of pregnancy to screen for the risk of Down's syndrome.

This test is not quite as accurate as the combined test. Check here for alerts. Your pregnancy and baby guide. Main navigation Getting pregnant Secrets to success Healthy diet Planning: When you can get pregnant Signs and symptoms When you can take a test Finding out Problems Help if you're not getting pregnant Fertility tests Fertility treatments Work out your due date When pregnancy goes wrong Sign up for weekly pregnancy emails. I'm pregnant Signs and symptoms of pregnancy Due date calculator The early days Week by week 4 to 8 weeks 9 to 12 weeks 13 to 16 weeks 17 to 20 weeks 21 to 24 how does a dating scan work 25 to 28 weeks 29 to 32 weeks 33 to 36 weeks 37 to 40 weeks 40 weeks plus Pregnancy week by week Twins Antenatal care with twins Pregnant with twins Healthy multiple pregnancy Getting ready for twins Preparing british dating culture the birth Where to give birth: Your health and wellbeing Healthy eating Foods to avoid Drinking alcohol while pregnant Exercise Vitamins and supplements Stop smoking Sex in pregnancy Pharmacy and prescription medicines Reduce your risk of stillbirth Illegal drugs in pregnancy Your health at work Pregnancy infections Travel If you're a teenager Existing health dating confidence Overweight and pregnant Mental health problems Diabetes in pregnancy Asthma and pregnancy Epilepsy and pregnancy Coronary heart disease and pregnancy Congenital heart disease and pregnancy Common pregnancy ailments Backache Bleeding gums Headaches Heartburn Itching Morning sickness Severe vomiting Pelvic pain Piles Stretch marks Stomach pain or cramps Swollen ankles Tiredness and sleep Vaginal bleeding Vaginal discharge More common problems Pregnancy-induced conditions Hyperemesis gravidarum Real story: The start of labour Signs of labour What happens when you arrive at hospital Premature labour Induction The birth What happens during labour and birth Forceps and ventouse delivery Pain relief Episiotomy What your birth partner can do Breech and transverse birth Caesarean Giving birth to twins What happens straight after the baby is born You after the birth Getting to know your newborn Emotions and worries Feelings and relationships Dads and partners If you have a chronic condition When pregnancy goes wrong Premature babies Premature or ill babies Premature baby: How to breastfeed Breastfeeding: Help for sore nipples Breast pain while breastfeeding Lifestyle and breastfeeding Breastfeeding and diet Breastfeeding and medicines Breastfeeding and smoking Breastfeeding and alcohol Going back to work Bottle feeding Bottle feeding advice Sterilising bottles Combining breast and bottle Making up infant formula Types of infant formula Infant formula: Weaning and solid foods Your baby's first solid foods Babies: What is the purpose of the dating scan?

The pregnancy dating scan All pregnant women in England are offered an ultrasound scan at around 8 to 14 weeks of pregnancy.

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Rachel Wood does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment. Republish our articles for free, online or in print, under Creative Commons licence. Radiocarbon dating has transformed our understanding of the past 50, years.

Professor Willard Libby produced the first radiocarbon dates in and was later awarded the Nobel Prize for his efforts. Radiocarbon dating works by comparing the three different isotopes of carbon. Isotopes of a particular element have the same number of protons in their nucleus, but different numbers of neutrons. This means that although they are very similar chemically, they have different masses.

The total mass of the isotope is indicated by the numerical superscript. While the lighter isotopes 12 C and 13 C are stable, the heaviest isotope 14 C radiocarbon is radioactive.

This means its nucleus is so large that it is unstable. Over time 14 C decays to nitrogen 14 N. Most 14 C is produced in the upper atmosphere where neutrons, which are produced by cosmic rays , react with 14 N atoms. This CO 2 is used in photosynthesis by plants, and from here is passed through the food chain see figure 1, below. Every plant and animal in this chain including us!

When living things die, tissue is no longer being replaced and the radioactive decay of 14 C becomes apparent. Around 55, years later, so much 14 C has decayed that what remains can no longer be measured.

In 5, years half of the 14 C in a sample will decay see figure 1, below. Therefore, if we know the 14 C: Unfortunately, neither are straightforward to determine.

The amount of 14 C in the atmosphere, and therefore in plants and animals, has not always been constant.

For instance, the amount varies according to how many cosmic rays reach Earth. Luckily, we can measure these fluctuations in samples that are dated by other methods.

Tree rings can be counted and their radiocarbon content measured. A huge amount of work is currently underway to extend and improve the calibration curve. In we could only calibrate radiocarbon dates until 26, years. Now the curve extends tentatively to 50, years. Radiocarbon dates are presented in two ways because of this complication.

The uncalibrated date is given with the unit BP radiocarbon years before The calibrated date is also presented, either in BC or AD or with the unit calBP calibrated before present - before The second difficulty arises from the extremely low abundance of 14 C. Many labs now use an Accelerator Mass Spectrometer AMS , a machine that can detect and measure the presence of different isotopes, to count the individual 14 C atoms in a sample.

Australia has two machines dedicated to radiocarbon analysis, and they are out of reach for much of the developing world. In addition, samples need to be thoroughly cleaned to remove carbon contamination from glues and soil before dating.

This is particularly important for very old samples. Because of this, radiocarbon chemists are continually developing new methods to more effectively clean materials.

These new techniques can have a dramatic effect on chronologies. With the development of a new method of cleaning charcoal called ABOx-SC , Michael Bird helped to push back the date of arrival of the first humans in Australia by more than 10, years.

Moving away from techniques, the most exciting thing about radiocarbon is what it reveals about our past and the world we live in. Radiocarbon dating was the first method that allowed archaeologists to place what they found in chronological order without the need for written records or coins. In the 19th and early 20th century incredibly patient and careful archaeologists would link pottery and stone tools in different geographical areas by similarities in shape and patterning.

Then, by using the idea that the styles of objects evolve, becoming increasing elaborate over time, they could place them in order relative to each other - a technique called seriation. In this way large domed tombs known as tholos or beehive tombs in Greece were thought to predate similar structures in the Scottish Island of Maeshowe. This supported the idea that the classical worlds of Greece and Rome were at the centre of all innovations.

Some of the first radiocarbon dates produced showed that the Scottish tombs were thousands of years older than those in Greece. The barbarians of the north were capable of designing complex structures similar to those in the classical world. Other high profile projects include the dating of the Turin Shroud to the medieval period, the dating of the Dead Sea Scrolls to around the time of Christ, and the somewhat controversial dating of the spectacular rock art at Chauvet Cave to c.

Radiocarbon dating has also been used to date the extinction of the woolly mammoth and contributed to the debate over whether modern humans and Neanderthals met. But 14 C is not just used in dating. Using the same techniques to measure 14 C content, we can examine ocean circulation and trace the movement of drugs around the body.

But these are topics for separate articles. See more Explainer articles on The Conversation. The rise of a university: Academy Workforce colloquium to explore the workforce pressures facing the health and social care system, involving education commissioners, the next generation of health and social care workers, representative bodies and politici — SWANSEA, Aberdeenshire.

The Paranoid Style Revisited: Available editions United Kingdom. Make no bones about it, radiocarbon dating has transformed our understanding of the past.

Dating history When living things die, tissue is no longer being replaced and the radioactive decay of 14 C becomes apparent. Carbon dioxide is used in photosynthesis by plants, and from here is passed through the food chain. Dating advances Radiocarbon dates are presented in two ways because of this complication.

Establishing dates Moving away from techniques, the most exciting thing about radiocarbon is what it reveals about our past and the world we live in. Your donation helps deliver fact-based journalism. You might also like Almost half of all people will experience haemorrhoids at some point. Morning smog in New Delhi, India. Expert Database Find experts with knowledge in: Community Community standards Republishing guidelines Friends of The Conversation Research and Expert Database Analytics Events Our feeds Donate Company Who we are Our charter Our team Our blog Partners and funders Contributing institutions Resource for media Contact us Stay informed and subscribe to our free daily newsletter and get the latest analysis and commentary directly in your inbox.

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Does anyone know how it is possible to date a pregnancy just by measuring the foetus during the ultrasound scan? It is the foetus size that they go by, isn't it? I am assuming that there is a range of healthy size at any given age, just like with newborns or any child, really, so how is the measurement more accurate than going by ovulation day? Welcome to Medical News Today. CT Scan or CAT Scan: How Does It Work? Computed tomography (CT), otherwise known as . Flaxseed and Prostate Cancer: Does It Work? Is there a link? Flax has roots dating back to ancient Egypt and China, making it one of the oldest fiber crops to be recorded.

Marshman Radiocarbon dating has transformed our understanding of the past Explainer: what is radiocarbon dating and how does it Rachel Wood does not work for. Flaxseed and Prostate Cancer: Does It Work? Is there a link? Flax has roots dating back to ancient Egypt and China, making it one of the oldest fiber crops to be recorded.