How many scans to expect when you're expecting

The New Zealand College of Midwives (NZCOM) and Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) both agree some pregnant women have too many ultrasound scans. They’ve teamed up to encourage women to question their need for them as part of the Choosing Wisely campaign.

Alison Eddy, chief executive of NZCOM, said maternity was an area where interventions could be applied “more liberally than they should be. We need to stop, question and re-examine the evidence”.

Dating scans

Dating scans, which are often performed around the seventh week of pregnancy, were one of those interventions she said needed questioning. As soon as a pregnancy test returns a positive result, most women are able to work out when their baby is due using one of the numerous due date calculators on the internet or with the help of their GP. All that’s needed is the date their last period started, something Ms Eddy said most women knew, but most were still sent off to get an ultrasound to determine their baby’s due date.

“They (doctors and midwives) give you a form for a blood test and form for a scan because that’s what they standardly do without stopping and thinking ‘why am I offering this’,” Ms Eddy said.

A scan can pick up issues that wouldn’t have any effect on the pregnancy but had the potential to make a woman anxious, Ms Eddy said.

“The thing with an ultrasound is it can only give you reassurance at that point in time. It doesn’t tell you what’s going to happen tomorrow or the next day,” - Alison Eddy, chief executive of NZCOM.

Dating can be done at the nuchal translucency scan (which can detect chromosomal abnormalities) at about the twelfth week of pregnancy. It’s one of two ultrasounds routinely offered to women, which Ms Eddy said were enough for most. The other is an anatomy scan, where a lot of important developmental problems can be picked up, around 20 weeks.

While a pregnant woman might be eager to see that flickering heartbeat and reassure herself all was well with her bub-to-be, Ms Eddy said they should instead be guided by the usual early pregnancy symptoms such as nausea, fatigue and having tender breasts. “The thing with an ultrasound is it can only give you reassurance at that point in time. It doesn’t tell you what’s going to happen tomorrow or the next day,” she said.

Rachael McEwing, a radiologist who is on the Maternity Ultrasound Advisory Group, said because unnecessary dating scans were being carried out, some women who really needed scans may not be able to get an appointment.

“Scanning resources are scarce in many parts of New Zealand and it should be a priority to perform scans in women who really need them rather than reassurance scans in women with a normal pregnancy,” Dr McEwing said.

“Sometimes they’re too early so we can’t say ‘yes the pregnancy is progressing normally’ or not, so they come for another scan and it’s still too early and some of these women have had six scans by the time they’re ready for their nuchal and none of them were really necessary. I don’t think it’s good for women, it creates a lot of anxiety.”

Ministry of Health statistics show a trend for pregnant women to have more ultrasound scans over the past five years. In 2017, the latest available figures, most had three to five scans. The ministry doesn’t record how many are being sent for dating scans.

Growth scans

Ms Eddy said another ultrasound women were too often being routinely sent for was a growth scan to check if the baby was bigger than normal.

“Measurements are put into a formula and an estimated weight is produced but there’s quite a bit of inaccuracy with that,” Ms Eddy said. “It can make women really anxious that their baby is really big and they’re not going to be able to give birth to it.”

"We need to try and change the culture for both women and GPs" - Lesley McCowan, head of the University of Auckland Obstetrics and Gynaecology Department.

An ultrasound diagnosis of a baby being large for its gestational age is associated with an increased risk of the baby being delivered by caesarean.

Dr McEwing said, like dating scans, unnecessary growth scans could result in a woman going on to have more scans. However, convincing women they didn’t need scans they’d come to expect was a challenge for practitioners.

“The process around having antenatal scans has become very socialised and women and their families come along for their scan excited to find out the gender of their baby. The purpose of the scan is to diagnose types of twins, to detect abnormalities and potential complications of the pregnancy such as placenta previa. Many families do not appear to be aware of this when they present for the scan.”

She said many came to scans in their third trimester expecting to leave with a 3D picture as a memento.

“We’re looking to see that baby is growing OK and the placenta is out of the way, and to exclude fetal abnormality.

“It’s become this expectation that it’s this big social event and it’s necessary you have these scans and it’s really not.”

Lesley McCowan, head of the University of Auckland Obstetrics and Gynaecology Department, said a culture change was needed.

“Women enjoy having a scan and seeing their baby is alive. I think it’s also become part of routine practice, which we’re trying hard to turn around,” Prof McCowan said.

“We need to try and change the culture for both women and GPs, who are often the first port of call when women confirm that they’re pregnant. We’ve got limited ultrasound resources in New Zealand and we need to make sure [scans are] available when we have a clinically indicated need for [them].”