Back to Your pregnancy and baby guide. 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. 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.
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.How accurate is ultrasound in dating a pregnancy?-Dr. Nupur Sood
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. Skip to main content. 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. Early days Your NHS pregnancy journey Signs and symptoms of pregnancy Health things you should know Due date calculator Week by week 4 to 8 weeks 9 to 12 weeks 13 to 16 weeks 17 to 20 weeks 21 to 24 weeks 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 for 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 Your baby's movements 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 problems 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: The best available data support adjusting the EDD of a pregnancy if the first ultrasonography in the pregnancy is performed in the third trimester and suggests a discrepancy in gestational dating of more than 21 days.
As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. For the purposes of research and surveillance, the best obstetric estimate, rather than estimates based on the LMP alone, should be used as the measure for gestational age.
how accurate is a dating scan?
The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine recognize the advantages of a single dating paradigm being used within and between institutions that provide obstetric care.
Table 1 provides guidelines for estimating the due date based on ultrasonography and the LMP in pregnancy, and provides single-point cutoffs and ranges based on available evidence and expert opinion.
No part of this publication may be reproduced, stored in a retrieval system, posted on the Internet, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Methods for estimating the due date. American College of Obstetricians and Gynecologists. Women's Health Care Physicians.
Recommendations The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine make the following recommendations regarding the method for estimating gestational age and due date: As soon as data from the last menstrual period LMP , the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record.
Introduction An accurately assigned EDD early in prenatal care is among the most important results of evaluation and history taking.
Women's Health Care Physicians
Clinical Considerations in the Second Trimester Using a single ultrasound examination in the second trimester to assist in determining the gestational age enables simultaneous fetal anatomic evaluation.
Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as the biparietal diameter and head circumference measured in transverse section of the head at the level of the thalami and cavum septi pellucidi; the cerebellar hemispheres should not be visible in this scanning plane the femur length measured with full length of the bone perpendicular to the ultrasound beam, excluding the distal femoral epiphysis the abdominal circumference measured in symmetrical, transverse round section at the skin line, with visualization of the vertebrae and in a plane with visualization of the stomach, umbilical vein, and portal sinus 8 Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role.
Conclusion Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. Fetal Imaging Workshop Invited Participants. A comparison of recalled date of last menstrual period with prospectively recorded dates. J Womens Health Larchmt ; Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol ; Last menstrual period versus ultrasound for pregnancy dating.
Int J Gynaecol Obstet ; First trimester ultrasound screening is effective in reducing postterm labor induction rates: Ultrasound for fetal assessment in early pregnancy.
Dating scan accuracy 13 weeks
Cochrane Database of Systematic Reviews , Issue 7. Predicting delivery date by ultrasound and last menstrual period in early gestation.
New charts for ultrasound dating of pregnancy and assessment of fetal growth: Ultrasound Obstet Gynecol ; First- and second-trimester ultrasound assessment of gestational age. First- vs second-trimester ultrasound: Br J Obstet Gynaecol ; Gestational age in pregnancies conceived after in vitro fertilization: Ultrasound dating at 12—14 weeks of gestation.
A prospective cross-validation of established dating formulae in in-vitro fertilized pregnancies. Accuracy of gestational age estimation by means of fetal crown—rump length measurement.
Estimation of gestational age by transvaginal sonographic measurement of greatest embryonic length in dated human embryos. Ultrasound Obstet Gynecol ;4: Underestimation of gestational age by conventional crown—rump length dating curves. New crown—rump length curve based on over pregnancies. Standardization of sonar cephalometry and gestational age.