Within 2 years of its release it became very obvious to most sonographers, sonologists and obstetricians that the 11-13.6 week scan gave much more information than the calculation of the Down Syndrome risk. The later the scan, the more foetal structure can be seen. 13-13.6 weeks gives the best information.
It is now apparent that we all failed to communicate this clearly. The public system and some private doctors still tell their patients that this 13-week scan is “optional” without explanation of its place in the management of a pregnancy. Some opt out because “they wouldn’t terminate a Down baby”. There seems to be no explanation that a termination cannot and will not be forced on anyone.
If they do intend to attempt to carry a Down baby to term, it must be kept in mind that Down babies have a much higher risk of stillbirth than their normal siblings. Counselling needs to be in place for the siblings and parents.
The parents and their precious baby’s welcome will be much better managed if everyone knows that the coming baby has Down Syndrome. This will allow emotional support to be more readily available for the parents. The early intervention for Down babies starts on day.
However, Nicolaides own statistics show that the ultrasound examination combined with blood tests miss about 13% of foetuses with Down Syndrome. Leading international researchers are now recommending using a risk of between 1:1,000 and 1:3,000 above which further invasive testing is offered. I now use 1:2,700.
Then the introduction of the NIPT, with great fanfare by Harmony, added a layer of confusion to the management of an early pregnancy. It needs to be remembered that the NIPT is a screening test with false positives for predicting deletion or translocation syndromes such as DiGeorge syndrome. It also has false negatives. It is not recommended to be used after a 13-week scan has predicted a high risk for a trisomy. Invasive foetal cell sampling is then needed.
Frequently the Non Invasive Prenatal Test (NIPT) such as Harmony and Generation is offered by medical practitioners as a replacement for the “old” 11-14 week Down scan. It is very reassuring that the foetus is found to be chromosomally normal. The parents can fairly reliably be told the sex if they wish to know.
The NIPT is not covered by Medicare for a reason, whereas the 13-week scan is.
Foetuses with enormous structural defects are very frequently genetically normal.
The pitfall of not realizing that the 13 week scan should be an early morphology scan and omitting it from the testing regime of an early pregnancy, removes the patient’s right to know that they are carrying a baby with a severe abnormality. These include an anencephalic or a severe spina bifida foetus, a foetus with a body limb stalk defect, a heart which is external to the chest wall, or a diaphragmatic hernia which has a zero chance of survival at birth, all of which are foetuses who are genetically normal.
These abnormalities and others will be found at the mid- trimester scan, that is at 20 weeks gestation leaving the difficult decisions to be made in a short timeframe and in the full glare of their friends and family’s opinions. It may lead to a traumatic induced labour and vaginal birth. It is creating, in effect, a situation of enormous trauma for the parents.
The other thing to keep in mind is that a “normal” 13 week scan does not and cannot exclude all structural defects as some have not yet developed.
With not having a 13 week scan there are missed opportunities of finding some structural defects and some significant pregnancy complications flagged by the first trimester trisomy blood screen. This is also frequently not understood, even by some obstetricians and radiologists.
A low PAPP-A is associated with an increased chance of preterm delivery before 34 weeks, an increased chance of foetal growth restriction (FGR) and an increased chance of intrauterine foetal death (IUFD).
Various studies use different significant levels. The lower the level, the greater the risk. Using a level of less that 0.42MoM, the odds ratios (OR) are approximately
Delivery < 34 weeks, OR 2.3
FGR, OR 3.0
IUFD, OR 2.3
With PAPP-A < 0.2 the risks are approximately doubled.
The actual numbers of patients having one of these conditions occurring is still quite low, however if detected prophylactic treatment and increased monitoring reduces the risks. There are some cases where a very low PAPP-A has manifested in a hypoplastic left heart at 20 weeks gestation the heart was normal at 13 weeks.
Uterine Artery doppler examination is quite easy at 13 weeks and should be done during the 13 week scan. It gives a good indication of whether there is a normal flow of blood to the uterus and the developing placenta or whether there is increased resistance to the blood flow as indicated by the doppler waveform. This particularly demonstrated by finding a notch in the diastolic flow on both sides.
A metadata analysis has shown the resistance pattern seen on doppler waveforms in both arteries has a positive predictive value of 95% with a false negative of 5% and a false positive of 2% for the prediction of severe early onset pre-eclampsia.
There have been many research publications with a variety of results. The final answer may be refined from the data above.
By promoting better placentation, aspiring improves the outcome in all of the above conditions.
The treatment, which has been proven to work by the use of double-blind studies in the UK’s NHS over a period of 5 years, is low dose Aspirin, taken at night. This must be commenced prior to 16 weeks gestation. The effect is dose dependant but is limited by increasing adverse events with higher doses.
The commonest dose used is 100mg a day but 150mg is more effective. A cheap soluble aspirin 300mg tablet broken in half with the unused have being discarded is a very good option.
I hope this clarifies the picture for you.
The 13 week scan with blood tests can offer much more than the risk of Down Syndrome and should be offered to all patients. It offers the chance to reduce the risk of some serious pregnancy complications. The NIPT is a complementary screening test which can be offered to all or selected patients.
Dr John. Howland Obstetrician Gynaecologist | QLD Australia
Web Design by MyWork
Dr John. Howland Obstetrician Gynaecologist | QLD Australia
Web Design by MyWork
