The low­down on ev­ery­thing you need to know about your an­te­na­tal scans

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What you need to know about all your an­te­na­tal tests

The ap­point­ments may only last 30 min­utes or so, but ul­tra­sound scans are defin­ing mo­ments in any preg­nancy. Ul­tra­sounds check your baby is grow­ing and as­sess the risk of ab­nor­mal­i­ties, such as Down syn­drome and spina bi­fida. Ad­di­tion­ally, many mums-to-be don’t re­lax un­til they see that first im­age of their ba­bies. Here’s what you can ex­pect from your an­te­na­tal scans.

How they work

An ul­tra­sound ma­chine emits high fre­quency sound­waves through a hand­held de­vice called a trans­ducer. They bounce off solid ob­jects, such as bone and or­gans, but pass through flu­ids, and are con­verted into an im­age of your baby.

Usu­ally, the first trimester screen­ing (of­ten re­ferred to as the 12-week scan) takes place be­tween weeks 11 and 14. At about 18 to 20 weeks, most women have a more de­tailed screen­ing, the foetal mor­phol­ogy (or anom­aly) scan.

Your scans will be 2D, but it may be pos­si­ble to opt for a 3D scan – for more de­tailed pic­tures – or even a 4D scan for pic­tures in real time, rather than stills. Since these are elec­tive ser­vices, they won’t be avail­able ev­ery­where, and the ex­tra costs in­volved won’t be cov­ered by Medi­care or pri­vate health in­sur­ance.

Name the date

Al­though you may have pin­pointed the night you con­ceived and have a date from your GP based on your last pe­riod, the 12-week scan pro­vides the most ac­cu­rate cal­cu­la­tion of your due date.

Your sono­g­ra­pher will mea­sure your baby from the top of her head to the bot­tom of her spine to con­firm the due date. Ba­bies grow at a set rate over the first 12 weeks, so the re­sults are very ac­cu­rate.

Remember to drink plenty of wa­ter be­fore the scan, as this will give the sono­g­ra­pher a clearer view of your uterus.

The big­ger pic­ture

As well as giv­ing you a time­frame for your preg­nancy, the 12-week scan will check for mul­ti­ple ges­ta­tions, so this might be the first time you find out you’re car­ry­ing twins or triplets. The 12-week scan also in­volves a nuchal translu­cency

(NT) scan to check for chro­mo­so­mal ab­nor­mal­i­ties, such as Down syn­drome.

The NT scan takes an im­age of the baby to mea­sure her length and the thick­ness of the pocket of fluid at the back of her neck.The re­sult is com­bined with a blood test (which ex­am­ines the lev­els of two spe­cific pro­teins: preg­nancy-as­so­ci­ated plasma and free beta hu­man chori­onic go­nadotropin) and the mother’s age to as­sess the baby’s risk level for Down syn­drome. While this method has an ac­cu­racy rate of about 85 per cent, it can only in­di­cate whether the baby has a high or low risk of ab­nor­mal­ity; it can­not pro­vide a de­fin­i­tive re­sult.

Mea­sur­ing up

The anom­aly scan is an anal­y­sis of the struc­ture of the baby to en­sure she’s grow­ing at the cor­rect rate. It in­volves tak­ing mea­sure­ments of her head, ab­domen and thigh bones. Your sono­g­ra­pher looks at her face (to rule out cleft lip) and spine (for de­fects such as spina bi­fida). The heart’s size and shape is also ex­am­ined to en­sure blood is flow­ing through it cor­rectly, and makes sure her stom­ach, kid­neys and blad­der are work­ing.

It’s ok to feel ner­vous

Go­ing to have a scan can be both ex­cit­ing and nerve-rack­ing. It’s nor­mal to feel scared, but your sono­g­ra­pher will al­ways ex­plain what or she is look­ing at. Your doc­tor will go through your re­sults and an­swer ques­tions about your op­tions. It’s im­por­tant to be pre­pared for any re­sult, even dur­ing rou­tine scans, but it’s equally im­por­tant not to worry un­nec­es­sar­ily.

Un­der the mi­cro­scope

As well as look­ing at the foe­tus, the ul­tra­sounds check your uterus. At the sec­ond scan, your sono­g­ra­pher will look at the po­si­tion of your pla­centa. If it’s near the top of your womb, it’s de­scribed as an­te­rior, which is good. If it’s at the bot­tom, you’ll need fur­ther scans in your last trimester. If it doesn’t move away as your baby grows, you may have pla­centa prae­via (where the pla­centa sits near or over the open­ing of your womb). You’ll be checked again at 32 weeks and, if it’s still in the way, you may be booked in for a cae­sarean. There will also be checks to en­sure blood is flow­ing nor­mally through the um­bil­i­cal cord and that there is enough am­ni­otic fluid.

Find­ing out the sex

This is usu­ally pos­si­ble at an anom­aly scan, but if bub is in an awk­ward po­si­tion, the gen­der may be tricky to con­firm. Not all ul­tra­sound cen­tres or hos­pi­tals will tell you the sex; check their policy. And if you don’t want to know, make this clear early on.

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