Preeclampsia is a condition characterized by high blood pressure in the pregnant woman, often exceeding the range of 140/90mm of Hg Systolic over Diastolic measured on two separate occasions 4 hours apart. (Note: It is important to take this measurement in a seated position) Preeclampsia is essentially when a normotensive woman with no prior history of hypertension conceives and due to placental pathology, her blood pressure escalates above the normal range within 20 weeks of conception. Since this condition is due to placental pathology, the blood pressure comes back to the normal within 12 weeks of delivery.
Placental Pathology of Preeclampsia
Normally, the cytotrophoblast replaces the lining of maternal arterioles and convert them from high resistance vessels to low resistance vessels. This process is called trophoblastic invasion. When this process is absent or incomplete, resistance in maternal arteries remains high which can predispose pregnancy induced hypertension. Apart from this, spiral arterioles normally undergo angiogenesis that increases the diameter and reduces pressure. This is due to the release of vasodilatory factors including Nitric Oxide and placental growth factors. In eclampsia, angiogenesis does not occur due to the absence of placental growth factor. Due to vasoconstriction and increased resistance in spiral arterioles, volume of blood coming to the placenta decreases, causing it to appear pale and ischaemic.
Symptoms of Preeclampsia
- Excretion of urinary protein ≥300mg in 24hours.
- Serum Creatinine ≥1.1
- Platelet count ≤1 lac
- Cerebral symptoms due to reduced blood flow to the brain.
- Edema due to release of inflammatory mediators that cause the blood vessels to be leaky leading to fluid accumulation.
- Maternal oliguria due to reduced blood flow to the kidneys, results in decrease of GFR.
- Epigastric pain due to stretching of liver capsule
- Scotoma, reversible blindness, blurring of vision and diplopia. Visual symptoms are due to hypertensive retinopathy and retinal detachment.
- If a female is exposed to chorionic villi for the first time, (primigravida)
- Excessive chorionic villi as in the case of Twin pregnancy/molar pregnancy.
- Placentomegaly as seen in gestational diabetes.
- Maternal age ≥35.
- Rh negative pregnancy.
- New paternity.
- Abruptio placenta.
- Antiphospholipid Antibody Syndrome (APLA).
- Metabolic X Syndrome/Obesity.
Therefore, placenta is the prerequisite for pregnancy induced hypertension and Preeclampsia and not the foetus as thought earlier. Chorionic villi can develop in extra uterine sites as well, therefore, preeclampsia has also been reported in females with ectopic pregnancies.
- Uterine artery Doppler. This is the most commonly used method which shows the presence of a diastolic notch on a graphical curve which should normally disappear by 22-24 weeks of gestation.
- Recent predictors use VEGF (Vascular Endothelial Growth Factors) and PGF (Placental Growth Factor) which are decreased in concentration along with reduced excretion of urinary calcium ≤12mg/dL in 24 hours.
- Free foetal DNA in maternal plasma.
- Reduction in Uric acid excretion reduces.
- Increase in Fibronectin
- Markers like Endoglin, Thromboxane A2 (TXA2) and PGI2 are increased.
Drugs to reduce the risk factors of Preeclampsia
- Best Drug Of Choice- Aspirin 50-150mg OD given between 12 weeks to 28 weeks. Continue throughout the pregnancy if patient develops Hypertension.
- Heparin and Aspirin.
- Calcium supplementation to calcium deficient females.
Why is Preeclampsia a cause for concern?
This condition is often accompanied by proteinuria or signs of end organ damage due to hypertension. It can be further divided into the mild form, where blood pressure is ≥140/90mm Hg with no signs of end organ damage and the severe form, where blood pressure is in excess of 160/110mm Hg with signs of end organ damage. Pre-eclampsia is dreaded is because it can lead to a life threatening condition called Eclampsia where the patient has generalized tonic clonic seizures. If this is not controlled, the patient can pass into refractory eclampsia or status eclampticus and ultimately coma.
Management of Pregnancy Induced Hypertension
- Definitive and preferred management is the immediate termination of Pregnancy, at 37 weeks of gestation for mild Preeclampsia and at 34 weeks of gestation for severe Preeclampsia. Vaginal delivery
- For impending eclampsia, administer Magnesium Sulphate to prevent convulsions. Magnesium sulphate is also a neuroprotective agent. It acts on the NMDA receptors in the brain, causes cerebral vasodilation and blocks Calcium channels which increases the seizure threshold. However, Magnesium Sulphate has a narrow therapeutic range and certain parameters need to be checked before repeating another dose. Give a second dose of Magnesium Sulphate only if there is knee jerk/patellar reflex, urine output ≥30mL/hour, Respiratory rate ≥12breaths per minute, SpO2 ≥ 96%.
- Look out for signs of Magnesium toxicity which include slurring of speech, diaphoresis, respiratory depression and cardiac arrest.
- Antihypertensive medications should be administered with the target blood pressure of 120/90mm Hg. Drug of choice is IV Labetalol. However, IV Labetalol is contraindicated in asthmatic patients.