Since there is no uniform criteria for diagnosis, the reported incidence is variable from 1/3000 to 1/6000 deliveries. Catanzarite (2001) in his study reported an incidence of 1/6227.

It is associated with a mortality of 45–90 %. If ARDS develops in antepartum, there is corresponding increase in perinatal mortality too.

ARDS in pregnant women can occur from obstetric or non-obstetric complications (Table 2.2).

The reduced albumin level and resultant reduced plasma oncotic pressure occurring in pregnancy lower the critical pulmonary capillary pressure at which pulmonary oedema develops (Pisani et al. 1989).

Chorioamnionitis is an important cause of pregnancy-specific infectious complication leading to ARDS. They present with fever, fetal tachycardia, uterine tenderness and foul-smelling amniotic fluid. In pregnant patients with ARDS without any clear cause, and without obvious symptoms of chorioamnionitis, diagnostic amniocentesis may be required [4].

Up to 7 % of pregnant women with pyelonephritis develop ARDS. Pregnancy-associated dilatation of the ureters, stasis and untreated bacteriuria in pregnancy increase the risk of acute pyelonephritis [2].

Viral/bacterial pneumonia, fungal infection and malaria are other infections linked with ARDS.

In about 3 % of patients with severe pre-eclampsia, ARDS is reported. Mostly 70 % occurs in immediate postpartum period. Elderly, multiparity and pre-existing chronic hypertension are the risk factors. Reduced pulmonary oncotic pressure, altered permeability of pulmonary capillary membranes and increased pulmonary vascular hydrostatic pressure all together contribute to the development of ARDS in pre-eclampsia. Placing pulmonary artery catheter must be individualised. It may help to distinguish fluid overload and cardiogenic pulmonary oedema from ARDS. But its use has not been shown to improve the outcome.

Supplemental oxygenation, mechanical ventilation and judicious use of diuretics are the mainstay in the management.

β-adrenoreceptor agonists like terbutaline and ritodrine were used previously for tocolysis. When used, in about 10 % of cases, ARDS developed, either during infusion or up to 12 h after discontinuation of the drug. In addition to pregnancy-related cardiovascular changes, factors like medicine-induced increase in heart rate and cardiac output, increased capillary permeability due to infection, myocardial dysfunction as a result of continuous exposure to catecholamines and aggressive volume resuscitation contribute to the development of ARDS.

Multiple gestations, maternal infection and the use of corticosteroids further worsen the condition. Because of such problems, magnesium sulphate is used for tocolysis in place of β-adrenoreceptor agonists.

Management include immediate stopping of the drug, supportive care and diuresis. Most of the time, it resolves within 12 h.

In pregnancy, aspiration of gastric contents is an important cause for ARDS, because of the physiologic and anatomic changes occurring in pregnancy and immediate postpartum. Enlarged pregnant uterus causing increased intra-gastric pressure, decreased tone of the gastro-oesophageal sphincter, reduced gastric motility and emptying, all predispose to aspiration. The well-known Mendelson’s syndrome of aspiration of gastric acid during obstetric anaesthesia was published in 1946 [5]. Once witnessed, the diagnosis of aspiration is easy. Otherwise visualisation of gastric contents in the pharynx during laryngoscopy at the time of intubation helps. The higher the volume, the lower the pH of the aspirated material and the more particulate the aspirated material, the worse will be the degree of lung injury. Perioperative aspiration pneumonitis is noticed in 0.11 % of CS and 0.01 % of vaginal deliveries.

Amniotic fluid embolism is another important pregnancy-specific cause of ARDS. It carries very high mortality. The entry of elements from the amniotic fluid into the maternal circulation could trigger the release of pro-inflammatory cytokines. AFE presents classically as acute hypoxic respiratory distress, haemodynamic collapse and DIC. The mortality rate is very high up to 80 %.

ARDS is characterised by three distinct stages: