Ultrasound exam A look at what your ultrasounds will involve. Having an ultrasound in the first trimester of pregnancy can be a thrilling experience. It's wonderful to see a little blob with a heartbeat that will become your baby. But ultrasounds can also lift the lid on a few worries you might be having. What if they can't see the heartbeat? What if it's smaller than it should be? Is there a problem? Bear in mind that you may need a second ultrasound before you know for certain if all is well.
When will I have my first ultrasound? If you are unsure of the first day of your last period you will be offered a dating ultrasound when you are between 10 and 14 weeks pregnant SOGC Can the dating ultrasound tell exactly how many weeks pregnant I am? 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.
The LMP is used because most women know when their last period was, but may not know when they actually conceived. If you do know the conception date, this is classed as day 14 and not day one.
If you have an irregular cycle, or if you've recently been taking the contraceptive pill, working out the date from your LMP isn't a very accurate method. Ultrasounds are more accurate than using the LMP Bottomley et al and, if the ultrasound date differs from your period dates, the ultrasound date will be used.
The ultrasound date is usually later than the period date, so accurate dating has been found to reduce the number of women having labour induced because their babies are overdue LeFevre et al , NICE What else will the dating ultrasound reveal?
The ultrasound can check that your baby has a heartbeat and is developing normally. Your baby's head, limbs, hands and feet, and some organs can be seen, and - though looking for abnormalities isn't the purpose of the ultrasound - some major problems can be seen at this early stage. You should still have a ultrasound between 18 and 22 weeks because more detail can be seen as your baby grows bigger.
The dating ultrasound will also show if you're expecting twins, triplets or more. 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. Knowing about twins early is also useful if you want to have screening for Down's syndrome.
This is because blood tests for Down's syndrome are not very accurate if you are having more than one baby. 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. What happens during the ultrasound? The ultrasound will take about five to 10 minutes. Nearly all ultrasound after 10 weeks can be done through your tummy, and most units ask you to come with a full bladder.
The sonographer will put some gel on your tummy and will move a small hand-held device, called a transducer, over your skin to get views of your baby. If your uterus is very deep in the pelvis or if you're overweight, you may be offered a vaginal ultrasound , which can get nearer to your baby.
It shouldn't be uncomfortable, and a big advantage is that you don't need a full bladder. The report from the ultrasound will be sent to your caregiver. It will tell you exactly how many weeks pregnant you are.
How big will my baby be at the dating ultrasound? Your baby is measured from head to bottom. This measurement, known as the crown rump length, is very accurate in the first trimester. After 13 weeks your baby can curl up and stretch out, so measuring the length becomes less accurate. Then the circumference of the head becomes the best way to measure your baby NICE At 10 weeks, your baby measures 3cm At 12 weeks, he measures 5cm to 6cm At 13 weeks, he measures 7cm Can I have a nuchal ultrasound at the same time as the dating ultrasound?
Nuchal translucency can be measured from 11 to 14 weeks to estimate the risk of Down's syndrome and other chromosomal abnormalities. Read more about screening for Down's syndrome. Some hospitals offer a nuchal translucency ultrasound to all women at 11 to 14 weeks, but this isn't available everywhere. Are there any disadvantages to having an ultrasound?
Sometimes having an ultrasound can cause unnecessary worry. It may show a very minor problem, or something which may get better on its own. As with all screening tests, there can be false positive and false negative results. For example, about one in 20 women will appear to be at high risk from the nuchal translucency ultrasound to assess the risk of Down's syndrome, but most of these babies will turn out not to have Down's syndrome. It's up to you whether you have an ultrasound - you don't have to if you don't want to.
If you're not sure, talk to your midwife. Read more about ultrasounds and safety. Take our quiz Now that you know all about ultrasounds scans, test your new-found knowledge by taking our quiz! Dating and growth in the first trimester.
National Down's Syndrome Screening Programme. A randomized trial of prenatal ultrasonographic screening: Am J Obstet Gynecol 3: National Institute for Health and Clinical Excellence, clinical guideline Routine care for the healthy pregnant woman. Royal College of Obstetricians and Gynaecologists. Antenatal Screening for Down's syndrome, setting standards to improve women's health. UK National Screening Committee. The rhetoric of "natural" in natural childbirth: Soc Sci Med 59 7: