5 frequently-asked questions about growth scans

Q: When can I have a growth scan? A: Growth scans can be performed in pregnancy usually between 24 and 34 weeks to check your baby is developing at the correct rate for your dates. Q: Why has my midwife suggested a growth scan now at 28 weeks - my 20-week scan was fine? A: Don't panic! Your midwife is just doing their job and keeping a close eye on your baby's growth and development. If they've suggested a growth scan there will be sound medical reasons for doing so. Growth scans are usually recommended if there are concerns about the size of your baby, or you've had complications in a previous pregnancy, or have a medical condition such as gestational diabetes, a type of diabetes where the body can't make enough insulin to meet the demands of pregnancy and where the danger is that your baby could grow too big. Pre-eclampsia, a type of high blood pressure that can affect blood supply to the placenta, is another condition that can restrict your baby's growth. All of these conditions require close monitoring of you and your baby's health, and this may mean you are recommended to have a series of growth scans over a couple of weeks to check on your baby. In some cases, a growth problem may mean that your baby is delivered earlier than usual by caesarean section.rnThere are also other perfectly natural reasons why your baby may appear small for dates. All babies develop at slightly different rates, for instance. Others are small because their parents are small or belong to a particular ethnic group, or they may just be lying in an unusual position. If your baby is close to full-term it may just be that their head is engaged in your pelvis and can't be measured accurately.   Q: Is it safe to have so many growth scans? A: Ultrasound scanning technology has been used routinely now for many decades in pregnant women and no adverse effects have yet been identified.Ultrasound scans remain the safest way of checking the health of your unborn baby. Q: What does a growth scan measure? A: A sonographer uses ultrasound to measure your baby's head, abdomen and thighbones, and then calculates its estimated birth weight. Bear in mind though that this is only an estimate and can vary by up to 25 per cent. It also gets much more difficult to accurately measure your baby when they are bigger. Your sonographer can compare the measurements with the average for babies of the same gestation to check your baby's growth is in the normal range and identify if there may be a problem with your baby's growth. A growth scan can also check on the amount of amniotic fluid around the baby; too much amniotic fluid or polyhydramnios has several causes including gestational diabetes in the mother and gut blockages in the baby. Having too little amniotic fluid(oligohydramnios) around the baby is a symptom associated with intra-uterine growth restriction (the medical name for poor fetal growth) - a condition that affects 3 in 100 babies - the two sometimes go together.rnThe majority of cases of poor fetal growth are caused by failure of the placenta, but other causes include infection and the demands of twins or multiple pregnancy. Checking blood flow from the umbilical cord to the placenta can reveal how well the placenta is functioning, if there are any problems, and identify the position of the placenta. All of these details are a useful source of information on your baby's general wellbeing. Q: I'm worried I'll have a small baby if I've been advised to have a growth scan - is this always a given? A: No it isn't. From 16 weeks of pregnancy your midwife will have relied on measuring your bump with a tape measure as a rough guide to your baby's growth - the medical name for this is the height of the fundus (fundal height). The measurement in cm from the pubic bone to the top of your bump usually equates to how many weeks pregnant you are - but it's not always accurate, particularly if you're overweight, have a full bladder or are carrying twins. Also, as your baby gets bigger, it's less accurate as babies grow at different rates in the third trimester. It may be that your baby will catch up on their growth or that they're just lying in an unusual position. Just because a growth scan has been suggested doesn't mean there's anything wrong with your baby, your midwife is just erring on the side of caution.