What is oligohydramnios?
Oligohydramnios means low fluid inside the amniotic sac.
(oligo = little, hydr = water, amnios = membrane around the fetus, or amniotic sac).
It is standard of care in the to induce women with isolated oligohydramnios at term.
What is amniotic fluid, and what does it do?
During pregnancy, the baby is surrounded by a liquid called amniotic fluid. Amniotic fluid helps protect the baby from trauma to the mother’s abdomen. Amniotic fluid cushions the umbilical cord, protects the baby from infection, and provides fluid, space, nutrients, and hormones to help the baby grow (Brace 1997).
During the second half of pregnancy, amniotic fluid is made up of the baby’s urine and lung secretions. This liquid originally came from the mother, and then flowed through the placenta, to the baby, and out through the baby’s bladder and lungs (Brace 1997).
This same amniotic fluid is then swallowed by the baby and re-absorbed by the lining of the placenta. Because the mother’s fluid levels are the original source of amniotic fluid, changes in the mother’s fluid status can result in changes in the amount of amniotic fluid. Amniotic fluid levels increase until the mother reaches about 34-36 weeks, and then levels gradually decline until birth (Brace 1997).
What can cause low amniotic fluid at term?
Both mother and baby factors can contribute to low amniotic fluid at term.
If the mother is dehydrated, this may lower the amniotic fluid levels. (Patrelli, Gizzo et al. 2012)
Women are more likely to be diagnosed with low amniotic fluid levels during the summer, possibly because of dehydration. (Feldman, Friger et al. 2009)
If a woman with low amniotic fluid levels at term drinks at least 2.5L of fluid per day, she increases the likelihood that her amniotic fluid levels will be back up to normal by the time of the birth. (Patrelli, Gizzo et al. 2012)
If the mother rests on her left side before or during the fluid measurement, this can increase amniotic fluid levels. (Ulker, Temur et al. 2012)
If the mother’s water has broken (membranes ruptured), this will lead to a decrease in amniotic fluid. (Brace 1997)
If the mother’s placenta is not acting sufficiently anymore, this may lead to a decrease in amniotic fluid. When this happens, it may be because the mother has a serious condition such as pre-eclampsia or intrauterine growth restriction. (Beloosesky and Ross 2012)
If the baby has a problem with the urinary tract or kidneys, this may decrease the flow of urine. (Brace 1997)
In the 14 days before the start of spontaneous labour, the baby’s urine output starts to decrease. (Stigter, Mulder et al. 2011)
As the baby gets closer to term, the baby swallows more amniotic fluid, thus leading to a decline in fluid levels. (Brace 1997)
If the baby is post-term (after 42 weeks), he or she begins to swallow significantly more fluid, contributing to a decline in amniotic fluid. (Brace 1997)
If the baby has a birth defect, he or she may swallow significantly more fluid, leading to low amniotic fluid levels. (Beloosesky and Ross 2012)
Reference: Science and Sensibility - August 2012
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