2.1.1 An abnormally low volume of amniotic fluid surrounding the fetus is termed oligohydramnios.
2.1.2 Oligohydramnios may be the result of decreased fetal urine production or excretion, or excessive loss of amniotic fluid. Causes of oligohydramnios include premature preterm rupture of amniotic membranes, congenital abnormalities of the fetus's urinary tract, placental insufficiency, twin-to-twin transfusion syndrome, post-maturity (more than 42 weeks' gestation), problems with maternal health, such as high blood pressure, and some medications. Severe oligohydramnios in early pregnancy may lead to the underdevelopment of fetal lung tissue (pulmonary hypoplasia) and limb defects and is associated with poor fetal growth. There is also an increased risk of miscarriage, premature birth and stillbirth.
2.1.3 Oligohydramnios is not routinely treated during pregnancy. There is some evidence that maternal hydration can increase the volume of amniotic fluid.
2.2.1 Under ultrasound guidance, isotonic fluid, such as normal saline or Ringer's lactate, is infused into the amniotic cavity via a needle inserted through the uterine wall, to restore the volume of amniotic fluid to normal. The procedure may be repeated on a regular basis if oligohydramnios recurs (serial amnioinfusion).
2.3.1 A randomised controlled trial of 34 pregnant women reported a significantly lower incidence of pulmonary hypoplasia among fetuses of pregnancies treated with amnioinfusion compared with the controls – (12% (2/17) versus 53%(9/17); relative risk 0.22; 95% confidence interval 0.05 to 0.87, p < 0.05). A non-randomised comparative study reported a rate of pulmonary hypoplasia among neonates of 23% (6/26) in the treated group compared with 31% (4/13) in the control group (not significantly different).
2.3.2 In a randomised controlled trial comparing amnioinfusion with expectant management, neonatal mortality was 6% (1/17) in both the treated group and the control group 6% (1/17). A non-randomised controlled study reported neonatal mortality (excluding stillbirths) of 18% (2/11) in the treated group compared with 71% (5/7) in the expectant-management group (p = 0.05). In another non-randomised comparative study, mortality within the first week after birth was 23% (6/26) in the treated group compared with 38% (5/13) in the expectant-management group (not significantly different). A third non-randomised comparative study reported a survival rate of 73% (8/11) for neonates treated with amnioinfusion and 21% (6/29) for those managed expectantly (p < 0.05). For more details, refer to the 'Sources of evidence' section.
2.3.3 The Specialist Advisers stated that key efficacy outcomes include prolongation of gestation, reduced incidence of pulmonary hypoplasia and improved neonatal survival.
2.4.1 A non-randomised comparative study including 45 women treated with serial amnioinfusion reported onset of labour shortly after the procedure in one case (2%).
2.4.2 One non-randomised comparative study reported miscarriage in 11% (3/28) of women with unruptured membranes and 21% (5/24) of women with ruptured membranes treated with amnioinfusion. A second non-randomised, retrospective case series reported miscarriage in 12% (2/17) of pregnancies. Four studies reported intrauterine fetal death rates ranging from 0% (0/15) to 14% (4/28) in pregnancies treated with amnioinfusion, and from 0% (0/14) to 38% (11/29) in pregnancies managed expectantly.
2.4.3 Other complications included placental abruption in 0% (0/11) to 25% (3/12) of cases and chorioamnionitis in 0% (0/11) to 32% (8/25) of cases. A study including 12 women treated with amnioinfusion reported that one neonate had a laceration on the leg that required sutures, which was attributed to the procedure. For more details, refer to the 'Sources of evidence' section.
2.4.4 The Specialist Advisers listed potential adverse events as including premature labour and delivery, fetal death, fetal trauma, infection, uterine perforation and premature rupture of membranes.