Pre-eclampsia screening in the first trimester – preemptive action to prevent the peril
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Pre-eclampsia complicating 2–5% of pregnancies is an obstetrical syndrome associated with deleterious short-and long-term consequences to the gravid women, the fetus and the neonate. Majority of the obstetrical complications occur in early pre-eclampsia (requiring delivery <34 weeks). The risk factor based approach recommended by the professional organizations for pre-eclampsia screening has shown suboptimal clinical performance. The combined multimarker screening for pre-eclampsia encompassing documentation of maternal medical history, measurement of mean arterial pressure, estimation of the maternal serum levels of placental growth factor, pregnancy associated plasma protein-A, and recording the Uterine artery mean pulsatility index, performed in the first trimester between 11 and 13 + 6 weeks has proven to be an effective screening strategy. The a-priori risk is determined by multivariate analysis of the factors from history, while the other parameters are converted to log 10 transformed multiple of median values. Bayes’ theorem is used to calculate the final risk. The above model has shown to detect 77% of preterm pre-eclampsia (<37 weeks), 96% of early preterm pre-eclampsia (<34 weeks), 38% of term pre-eclampsia and 54% of all pre-eclampsia, at a false positive rate of 10%. Uterine artery Doppler is key to pre-eclampsia screening. Currently a risk of >1:100 for pre-eclampsia developing before 37 weeks (preterm pre-eclampsia) is regarded as screen positive. Aspirin at a dose of 150 mg at bedtime given to screen positive subjects is associated with a significant reduction of preterm pre-eclampsia and early pre-eclampsia. The intervention is now supported by a well conducted randomized trial and metanalysis data. Aspirin acts by diminishing stores of constitutive cyclooxygenase enzyme in the non-nucleated platelets without disturbing systemic prostaglandin production. Selective use of aspirin in screen positive women is associated with a very low incidence of adverse maternal, fetal and neonatal side effects. The screening protocol can be applied to twin pregnancies albeit minor differences. Hence, screening for pre-eclampsia in first trimester, which is now endorsed by the federation of international obstetrical and gynecological societies, should be offered universally to all women at 11 to 13 + 6 weeks of gestation, followed by the administration of aspirin and serial maternal-fetal surveillance in the screen positive woman.