Reduced amniotic fluid volume
Is reduced amniotic fluid volume a matter for concern?
Yes. Even though, in a good number of cases, no cause for the reduction of the volume is ever established, reduced fluid volume may signal such problems as fetal abnormality, suboptimal placental function, unrecognized rupture of membranes or even wrong dates. Reduced amniotic fluid volume always calls for closer monitoring of the pregnancy.
What sort of -fetal abnormalities would one worry about in the presence of reduced fluid volume?
The main concern is kidney or other urinary tract abnormalities.
If the baby has one of the few serious kidney abnormalities that makes them unable to produce urine, then there will be very little - almost undetectable - amniotic fluid. This is usually apparent very early, probably around twenty weeks of gestation. An ultrasound scan will go a long way in establishing the diagnosis but this is not always possible.
If there is a condition that obstructs the flow of the urine, again there will be reduced fluid volume.
As a rule, the defects have to be bilateral (affecting both kidneys) to produce this effect.
Is there anything that can be done in the presence of such abnormalities?
It depends on the diagnosis or potential diagnosis. Some kidney abnormalities are incompatible with life outside the womb. Most obstructive conditions can be relieved before delivery, if this is found to be necessary. This is usually a stop-gap measure.
The attending obstetrician will explain in detail what the suspected or confirmed diagnosis is and the proposed course of action.
What about sub-optimal placental function?
If the placenta, for whatever reason, is not functioning efficiently, this may be reflected in reduced amniotic fluid volume. There will also be restricted growth of the fetus.
If these features are apparent, the progress of the pregnancy will be monitored closely and there is a high possibility of induction of labour even before reaching term. Each case is obviously assessed on its own merit, and there is no hard and fast rule.
Can genetic or chromosomal abnormalities cause reduction of fluid volume?
Yes. Some chromosomal abnormalities are characterised by a chronically reduced fluid volume, almost always accompanied by fetal growth restriction. Because many of these abnormalities occur with other physical abnormalities, the diagnosis is likely to be suspected before delivery.
If this is the case, fluid could be taken from around the baby (by a procedure called amniocentesis) for analysis, to establish the diagnosis.
Does reduced fluid volume have any adverse effect on the growing fetus?
Yes. The most feared effect is poor lung development. Normal lung development depends on the presence of sufficient amniotic fluid. If the reduced volume starts very early and does not improve, lung development could be very poor and this is an extremely difficult problem to overcome.
The severity of this problem also depends on the degree of reduction in the fluid volume.
What are the other complications of low fluid volume?
The baby may be born with limb deformities, which are normally correctable. It is usually the feet that are affected (known as talipes or "club foot"). There is also an increased risk of fetal distress and delivery by caesarean section. As mentioned before, premature delivery - either spontaneous or induced - may be unavoidable.
What about rupture of the membranes?
Yes, this is also a cause of reduced amniotic fluid volume. In virtually all cases, this is immediately apparent. A complication unique to this is the risk of infection affecting the pregnancy. This significantly increases the risk of losing the baby. Labour tends to occur soon after rupture of the membranes, that is, within days.
However, it is not unknown for the pregnancy to continue for several weeks after rupture of the membranes.