|
|
|
Small for Gestational Age (SGA ) babies –why does it matter?
As you can see from the table in the smoking in pregnancy section, SGA is one of the largest consequences of smoking in pregnancy. SGA can have life-long consequences. There is increased perinatal mortality and a risk of stillbirth- 50% of stillborn babies are SGA. SGA can also increase the risk of cerebral palsy and cause developmental delay. As adults these babies are at increased risk of diabetes and cardiovascular disease such as stroke and heart attack. You will also discuss SGA in Case 7.
So how do we define what is meant by SGA? Previously SGA was defined as birth-weight <10th centile for a population of births. In NZ these population centiles were derived largely from European births and they underdiagnosed SGA in Pacific women and over-diagnosed it in Indian/Asian women. We now define SGA as an infant with birth-weight <10th customized centile. Customized centiles adjust the birth-weight for some maternal factors which influence birth-weight [height, weight, parity, ethnicity (see information below)] as well as infant sex and gestation at delivery. Customized centiles better identify small babies at risk of complications.
Here is a diagram of the pathophysiology of SGA to have a look at.
Also have a look at some SGA risk factors :
In the general population.
In addition to maternal height and weight, ethnicity itself also has an effect on baby size. NZ figures show that the mean birthweight for Pacific island women is 3.54kg, compared to 3.43kg for European, 3.32 kg for Māori and 3.24kg for Asian women. So Māori and Indian women have lighter babies than European women and Tongan and Samoan women have heavier babies.
Data suggest that only 20-40% of SGA babies are currently detected before they are born. All of the issues we have talked about have to be taken into account to enable improved antenatal detection and this has led to the development of customised growth charts - GROW. These are computer generated curves adjusted to the characteristics of each pregnancy. They help predict optimal fundal height and fetal weight at term for individual pregnancies (adjusted for maternal height, weight, ethnicity and parity) and have been shown to double the detection of SGA babies. This is important as better detection of these small babies before birth may ultimately result in fewer perinatal deaths.
When accompanied by risk identification and optimum management of SGA, pregnancy outcome is likely to improve with use of these customised charts. (J Gardosi Association between reduced stillbirth rates in England and regional uptake of accreditation training in customised fetal growth assessment. BMJ Open 2013; 3: e003942 doi: 10.1136/bmjopen-2013-003942).
The NZ edition of GROW can be accessed within most maternity units. Ask someone to show you how to create a customised growth chart for a patient. www.gestation.net/grow-nz.aspx
ACTIVITY - which baby may be SGA?
Have a look at these two GROW centile charts for two different women. Both contain some lower fundal height measurements than average, however only one of the mothers needs to have an ultrasound scan to check on the baby. Which mother is that - the Indian or the Samoan and why?
Check your answer with other students and talk to your clinicians and see if you have got it right!!!
So if a woman is at high risk of SGA, what is the plan?
Click here to see our suggestion
- Smoking cessation if smokes
- Advice re healthy diet
- Specialist consult
- Low dose aspirin from 1st trimester and before 16 weeks (reduces risk of SGA and preeclampsia) (Bujold E et al. Prevention of pre-eclampsia and intrauterine growth restriction with aspirin starting early in pregnancy: a meta-analysis. Obstet Gynecol. 2010;116(2, Part 1):402-14.)
- Generate a customised growth chart. To do this, measure maternal height and weight at booking or as early into the pregnancy as possible.
- Plan for serial growth scans 4 weekly and more frequently if deviation from expected growth trajectory is detected.
- And even if the scans are OK initially, continue these until term
- Plot fetal weight measurements on customised growth chart, as well as the standard ultrasound chart. Even if the customised chart is showing normal growth, but the abdominal circumference is slowing in growth, or on a much lesser percentile line that the fetal head and femur measurements, care needs to be escalated as this baby may also be growth restricted.
Edit page
