Can we scientifically identify Low-risk subjects of Preeclampsia?

 

Not being high-risk does not necessarily mean one is low-risk. It is well known that amongst many parameters to identify potential subjects for developing preeclampsia, nearly all are for identifying high-risk subjects. However there is hardly any research work published that can guide us to low-risk subjects. These are the days of not stopping at identifying high-risk but actually identifying low-risk subjects of preeclampsia.

Why do we need to identify the low-risk subjects also?

It has been found in clinical practice long since that not being high-risk does not necessarily mean one is low-risk. There are majority of subjects who are not high-risk but are also not necessarily low-risk. As a result we all are over using prophylactic measures. Also we are scared to stop prophylaxis once a subject is labelled high-risk and is never tested again. While pregnancy is a dynamic state, it surely happens that some subjects who may be high risk initially may cease to be so as pregnancy advances due to multiple reasons. Why then to continue prescribing them prophylactic measures. Some of them can be very costly and nearly all can have side effects. This blog shares scientific research data with you by which you can identify low-risk pregnant subjects for preeclampsia. 

How does it help in preeclampsia and OVs?

More than three decades ago our group started working to decode the mysteries of preeclampsia. In this aspirin emerged as a front-runner for prevention. I first spoke on this sharing results of my work at AMOGS conference in Meeraj in 1992. Since then much water has flown under the bridge. I was once asked by the chairman at the session where I was giving my lecture in Sri Lanka as to whether it will be all right to start giving Aspirin to all pregnant subjects. This made me respond “Why to give it to low-risk” subjects. Around this time I was also working on low-dose heparin in prevention of major OVs. If one is able to identify low-risk subjects clearly then these preventive medications need not be given. This makes the management more scientific and focused.

Tools to identify low-risk subjects

Currently the nearly universal tool used is the tool of default. This means if a subject is not high-risk, she is low-risk for these conditions. Such a thinking is wrought with error and fallacy. All of us are familiar with the fact that there always are subjects who may not be high-risk when prediction methods are used. This is usually around 12 weeks of pregnancy. But they can still develop preeclampsia as pregnancy rolls on. No wonder we have a recommendation of using more than one set of tools for prediction. The most recommended are Colour Doppler and biochemical markers along with the clinical obstetric history of the subject.

In set-ups like those where we are working there are many practical and logistical disadvantage of the combination. The biochemical methods are costly and need an extra time-consuming visit to the laboratory. We have been able to provide a solution to this. We use more than one colour Doppler parameters to identify “low-risk” subjects for preeclampsia and other late OVs.

The reason for using more than one parameter is to increase the accuracy of the results. This is precisely the reason why biochemical markers were studied and used in combination with colour Doppler. Using the same basis, we are using more than one colour Doppler parameters to identify low-risk subjects with very good results.

Our Results:

This prospective longitudinal study was conducted to identify subjects who are at a low-risk for developing preeclampsia remote from term. Most of the currently popular studies identify high-risk subjects. Also, they usually use a biochemical parameter. The present study identifies low-risk subjects only on the basis of two parameters of uterine artery color Doppler in first-trimester of pregnancy and did not use any biochemical parameter.

Materials and Methods

           All singleton pregnancies that registered in the first trimester were included for this study. Uterine artery color Doppler was performed between 11-13⁺⁶ weeks. Subjects who showed a Pulsatility Index (PI) PI≤1.0 and absent Diastolic Notch (DN) in both uterine arteries were prospectively followed up for development or otherwise of preeclampsia before 32 weeks of pregnancy. Their outcome was compared with that of subjects with other groups. Two tools of statistical analysis were used. Chi-square test for calculating the P-value and sensitivity, specificity, positive and negative predictive value calculations were done for drawing accurate conclusions from the results. 

Results:

          510 pregnant subjects were prospectively followed-up in this study.

TABLE: Statistical Groups with Distribution of Cases

 

Uterine Artery Doppler at 11-13+6 weeks	Developed Preeclampsia?	Number
PI≤1 and DN Absent	Did not develop  Preeclampsia	47
PI≤1 and DN Present	Did not develop  Preeclampsia	157
P>1 and DN Absent	Did not develop  Preeclampsia	13
P>1 and DN Present	Did not develop  Preeclampsia	211
PI≤1 and DN Absent	Developed Preeclampsia	7
PI≤1 and DN Present	Developed Preeclampsia	24
PI>1 and DN Absent	Developed Preeclampsia	3
PI>1 and DN Present	Developed Preeclampsia	48
TOTAL		510

(Key: PI = Pulsatility Index, DN = Diastolic Notch)

On statistical analysis, it was found that subjects with a combination of PI≤1 and absent DN had a very significantly less likelihood of developing preeclampsia making them low-risk subjects. On applying one more tool of statistical analysis these results were found to have a very high sensitivity and negative predictive value.

Comment:

          The combination of uterine artery PI≤1.0 and an absent diastolic notch at 11-13⁺⁶ weeks USG scan is effective to identify subjects at low-risk of developing preeclampsia remote from term. This is essentially a one-step method not relying on any separate biochemical markers for its efficacy. While the presence of these findings on color Doppler identified low-risk subjects effectively, the absence of these findings does not automatically indicate a high-risk subject. This is a statistical limitation of this study. Additional research can help in confidently using these tools in clinical settings.

Conclusion:

The combination of uterine artery PI≤1.0 and an absent diastolic notch at 11-13⁺⁶ weeks USG scan is effective to identify subjects at low-risk of developing preeclampsia remote from term.

Note:

For accessing the full text of this paper please click on: https://www.drpankajdesai.com/MRP/1.htm