Oligohydramnios-Causes and diag of Pulmnary hypoplasia

What may be causes of oligohydramnios?? Ans: in addition to foetal urinary tract anomalies and in the absence of PROM, uteroplacental insufficiency should be considered. Oligohydramnios may result from poor placental transfusion with 1) maternal hypertension, 2) chronic placental abruption and 3) autoimmune states such as systemic lupus and antiphospholipid syndrome.

What about foetal AC in oligohydramnios ?? Ans.  Foetal AC  is almost always low. In cases of oligohydramnios fetal abdominal circumference growth typically lags that of the head. Also, the increased placental vascular resist­ance evident on umbilical artery Doppler studies may help corroborate the diagnosis of oligohydramnios due to placental insufficiency.

The risk of fetal asphyxia and death is high when severe oligohydramnios accom­panies intrauterine growth restriction (FGR). Intensive fetal testing and hospitalization should be considered in cases diagnosed after the point of fetal viability .  After 32 weeks, severe oligohydramnios and fetal growth restriction should generally lead to evaluation for delivery.

How to assess likelihood of pulmonary hypoplasia??

Ans:- By measureing of chest circumference, use of thoracic-head circumference ratio, calculating the lung area ratio [(chest area-cardiac area)/chest area] It appears that the risk of pulmonary hypoplasia is greatest when severe oligohydramnios is present from 16 to 24 weeks of gestation, the period of alveolar proliferation.

Longstanding oligohydramnios predisposes to pulmonary hypoplasia. Although the mechanism of this potentially lethal complication is not clear, inhibition of fetal breathing, loss of lung liquid because of reduc­tion in amniotic pressure, and simple mechanical compression of the chest have been proposed the end result is restricted lung growth leading to alveolar volume inadequate to support postnatal respiration.  Though several methods have been proposed to predict pulmonary hypoplasia, no single criterion has adequate sensitivity and specificity for clinical decision-making.(Measurement of chest circumference, use of thoracic-head circumference ratio, calculating the lung area ratio [(chest area-cardiac area)/chest area] and thin-slice three-dimensional fetal lung volume/fetal body weight ratios have been proposed to assess the pres­ence of pulmonary hypoplasia.

Recently, magnetic resonance imaging and Doppler assessment of fetal pulmonary tissues have also been utilized for prediction of pulmonary hypoplasia. Use of MRI-based abnormal lung volume/fetal weight ratio , is assed in research  settings gave a sensitivity of 88% with a false positive diagnosis of pulmonary hypoplasia of 12%. When chest development appears markedly compromised in a pre-viable fetus with severe oligohydramnios, the option of termination of pregnancy should be discussed within legal frame work of our country.