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Treatise on Polyhydramnios

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As a homebirth midwife, all I "need" to know about polyhydramnios is how to detect it and that I then need to refer, probably for transfer of care as polyhydramnios isn't a real candidate for homebirth. (Mind you, it's probably still safer at home than in a hospital, but it won't hold up in front of a jury, so . . .) This is focused on the mechanics of birthing for a mom with polyhydramnios.

Polyhydramnios - Definition, Incidence, Causality, Prognosis

Polyhydramnios is a condition in which the pregnant uterus contains too much amniotic fluid. The definition of "too much" is generally considered to be more than 2 liters; the average amount is about 1 liter. Most cases of polyhydramnios are mild and involve less than 3 liters of amniotic fluid. So, in many cases, a diagnosis of polyhydramnios means that you're on the high side of normal for amount of amniotic fluid and presents only minor secondary concerns.

Polyhydramnios occurs in about 1 pregnancy out of 100; 95% of those are considered mild to moderate.

Some background on amniotic fluid: As with many issues in human biology, mechanisms of regulating the amount of amniotic fluid are not well understood. It is believed that amniotic fluid is manufactured by the amnion, which "weeps" to add fluid. In addition, babies urinate and sweat, also adding to the fluid. Fluid is removed from the amniotic sac when the baby swallows and the fluid is taken into the bloodstream and transferred to the mother's bloodstream via the placenta.

The cause is rarely known for certain, but a diagnosis of polyhydramnios will usually result in a search to find the cause, typically through ultrasound. The ultrasound may or may not reveal the likely cause in the form of a fetal abnormality.

In about 60% of cases of polyhydramnios, there is a mild to moderate amount of excess fluid caused by more-than-adequate generation of fluid by the amniotic sac. The mother and baby are completely normal, and the only concerns are the mechanical issues relating to the large amount of fluid at labor and delivery. This type of polyhydramnios tends to appear after about the 30th week, when there is a gradual increase in the amount of fluid. It is detected by higher-than-average growth of the uterus, difficulty in feeling the outline of the baby because of the generous amount of fluid, difficulty in hearing the baby's heart because of the amount of fluid, and the ability to create waves in the fluid. It tends to stabilize in volume or increase very gradually and is simply a variation on normal. This is generally an indication that there are no serious congenital problems, and the only remaining concerns are the mechanical issues around labor and birth related to a large amount of amniotic fluid. (This is called "chronic hydramnios.")

In another 20% of cases, there is a problem on the maternal side, either diabetes or a blood incompatibility with the fetus. These cases require close monitoring by a specialist because the cause of the polyhydramnios could represent a serious problem for the baby.

In another 20% of cases, there is a problem with the baby - either the baby is adding unusual amounts of fluid or is swallowing less than usual. A blockage of the esophagus that prevents swallowing is usually easily remedied by postpartum surgery. Excess amounts of fluid are thought to be caused by increased fluid coming from the exposed spinal cord or by excess urination caused by overstimulation of the exposed spinal cord, as in anencephaly or spina bifida.

Again, none of these mechanisms is understood thoroughly; there is simply evidence correlating some of these conditions. Severe cases of polyhydramnios tend to be associated more with fetal abnormalities and tend to have a worse outcome. In most mild to moderate cases, a cause is never identified and the outcomes are completely normal.

Severe polyhydramnios tends to appear at about the 20th week of pregnancy and tends to have a sudden onset, i.e. the uterus will have grown 8 cm in 4 weeks rather than the expected 4. This type of polyhydramnios is more likely a symptom of a serious congenital problem. In addition, the amount of amniotic fluid tends to increase, often to the point that the amniotic sac ruptures or premature labor begins. In many of these cases, premature delivery of an immature infant results in the death of the fetus.

Polyhydramnios as it Relates to Labor and Birth

Having a large amount of amniotic fluid can cause mechanical problems having to do with the baby's presentation, and the possibility of cord prolapse, placental abruption and postpartum hemorrhage. Let's look at each of these in turn, and consider why there's a risk and what can be done to minimize the risk.

THE BABY'S PRESENTATION: A baby normally settles into a nice, head down position as the growing body crowds the uterus and finds that it is best accommodated with the bulkier bottom in the roomier top of the uterus. With a lot of amniotic fluid, this will happen later in the pregnancy than usual. Occasionally, even a fullterm baby may have room to turn freely. Thus, the presentation (i.e. head down, breech or an unfavorable transverse lie) continues to change until the amount of fluid is reduced, typically when the membranes rupture. Because this can be a sudden event, the baby may be caught in an awkward transverse lie, which is impossible to birth vaginally. In addition, many practitioners are not trained in safe, vaginal delivery of breeches and consider a breech presentation an indication for a cesarean section.

Thus, the baby's presentation at the time the amniotic sac ruptures is a major factor in the subsequent course of the delivery. So, it is essential that some intelligence be brought to the situation. Ideally, the baby is encouraged to assume an ideal, head down position, and the membranes are ruptured very slowly, i.e. with a small pinprick to allow the waters to begin to leak out. Then the baby may be held in position until enough fluid has leaked out that the baby can no longer turn.

Because of the possibility of cord prolapse, this should be done by a caregiver trained in this technique. Also because of the possibility of placental abruption, it is essential that there be ready access to an emergency cesarean.

CORD PROLAPSE: Cord prolapse is a situation in which the umbilical cord comes before or alongside the presenting part. This is a problem because the cord may become compressed in the pelvis and blood may not be able to flow freely through it to the baby.

Polyhydramnios increases the risk of cord prolapse for several reasons. First, because the baby's presentation is unpredictable, the baby may be in an unfavorable position when the membranes rupture, and the presenting part may not fit into the pelvis well enough to keep the cord from falling out below. Second, because there is so much fluid, there is more pressure on the movable umbilical cord to move it out past the presenting part.

This risk can be minimized by managing the rupture of membranes, paying close attention to the baby's presentation. If the membranes are ruptured with a pinprick while the baby's head is held low in the pelvis, the risk of cord prolapse can be minimized.

PLACENTAL ABRUPTION: A placental abruption is a premature separation of the placenta from the uterine wall. This is a problem because it interferes with the free flow of blood between the maternal blood supply and the fetal circulatory system. A partial abruption may not be a serious problem, but if a significant portion of the placenta separates, the baby's oxygen supply is compromised so that the baby may begin to suffer severely from oxygen deprivation and may die. A significant placental abruption is a situation that warrants an immediate cesarean section to save the baby.

Polyhydramnios increases the risk of placental abruption because of the mechanical forces at work in separating the placenta from the uterus. If you can imagine a filet of tofu (this is a vegetarian explanation) glued to the top of an inflated balloon, this is sort of what a placenta looks like inside the uterus. When the balloon starts to deflate, the amount of inside surface to which the tofu is attached starts to decrease. The tofu will start to buckle and separate in places and then may shear off partially or completely. This is less likely to happen if there is a small amount of deflation, and more likely to happen if there is more deflation. (By the way, this is also the way the placenta normally separates after birth, after the baby has been born. It is only a problem if it happens before the baby's birth.)

When there is an unusually generous amount of amniotic fluid, the difference before and after rupture of membranes may be significant, especially if the presenting part does not fit well into the pelvis and seal the remaining fluid in the uterus. This sudden change in uterine size may cause a placental abruption. If there is only a mild to moderate amount of extra amniotic fluid, this may not be a problem. In any case, it is important that the presenting part be fit as snugly into the pelvis as possible so that the continuing production of amniotic fluid may fill the upper part of the uterus and guard against a placental abruption. (And, in a situation of polyhydramnios, this should happen even more readily than otherwise.)

However, given the dire consequences of a placental abruption, it is essential that there be ready access to a cesarean section until membranes have ruptured and the amount of amniotic fluid has stabilized.

POSTPARTUM HEMORRHAGE: Polyhydramnios increases the risk of postpartum hemorrhage simply because the uterus has been distended more than is usual for a singleton pregnancy. Thus, it can be more difficult for the uterus to contract completely, and it is essential that a diligent watch be kept to ensure that clots do not accumulate, thus making it even harder for the uterus to contract, thus causing more bleeding, more clots, etc. Diligent attention to uterine size and hardness should provide ample warning of impending postpartum hemorrhage. Massaging the uterus or nursing the baby (or otherwise stimulating the nipples) will help to keep the uterus contracted. It may be necessary to augment this with pitocin.

Herbals for postpartum hemorrhage: Red raspberry leaf tea can be used during pregnancy to tone the uterus, so that it contracts more effectively to prevent postpartum hemorrhage. Motherwort herb can be used after the delivery of the placenta to prevent postpartum hemorrhage, and shepherd's purse can be used to stop a postpartum hemorrhage.


_Williams Obstetrics_ recommends amniocentesis to relieve maternal distress and hints that it will also lessen risks of cord prolapse and placental abruption. However, there are no other guidelines for standard obstetric management of the delivery. There is a specific guideline *not* to rupture membranes artificially because of the risks involved, but there is no discussion of how to manage the inevitable rupture of membranes intelligently.

Since I am a homebirth midwife, I am required to transfer or co-manage care of polyhydramnios. So I don't have a protocol for management of delivery in the presence of polyhydramnios. However, as someone who lives in Earthquake Country, I like to learn as much as possible, just in case. If, in an emergency, I were attending a homebirth delivery of a woman with polyhydramnios, I would probably do the following: Assuming the membranes were not yet ruptured, my first thoughts would be to encourage the baby to get in a head down position through slantboard exercises, homeopathics, visualization, headstands in pool if possible. If a complete version is not possible, I would help the baby at least to get into a longitudinal lie, rather than transverse. (So either head down or breech would be OK.) Once labor is well established and the presenting part engaged, I would have the woman get in a knees-chest position, have an assistant hold the presenting part low in the pelvis and put a pinprick hole in the bag of waters. Then, very slowly, while listening to the baby's heart rate, I would help the woman to assume an upright position as the waters slowly leaked out. Assuming all is well and the presenting part well engaged in the pelvis, we are then past the problems of presentation, cord prolapse and greatest danger of placental abruption. All that remains is to keep a watchful eye on things and be prepared to prevent and/or treat a postpartum hemorrhage.


Polyhydramnios simply means that there is more amniotic fluid than is usual. In most cases, it is just a variation on normal, appearing gradually late in the pregnancy and posing some minor additional challenges for the labor and delivery. In about 5% of cases, the condition is severe and usually correlated with a severe fetal abnormality; these cases tend to develop suddenly at about 4 or 5 months. In severe cases, a continuing increase in the amount of amniotic fluid threatens the pregnancy, which may end in premature delivery.

In most cases, no cause is identified; the only reason it is of any significance is that the increased amount of fluid must be dealt with intelligently in order to avoid problems in labor and delivery. Particular attention must be paid to assisting the baby in getting into a favorable position for the birth. The amniotic sac must not be allowed to rupture so that there is a sudden loss of amniotic fluid; this could cause a cold prolapse or a placental abruption. The birth attendants must be alert to prevent and treat possible postpartum hemorrhage.

This Web page is referenced from another page containing related information about Miscellaneous Prenatal Information


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