Women with neuromuscular disorders are receiving better treatment, surviving longer and feeling better, and some women want to start families. Many may consider the possibility of passing on a genetic disease to their babies and may assess their own strength for carrying through a pregnancy and taking on the demands of motherhood. But relatively few women fully understand the potential medical complications they and their babies may encounter.

The doctors we talked to thought the following were the most important complications for women to consider. Those marked with a yellow traffic light are those doctors consider serious, but manageable with planning and monitoring. A red light indicates pregnancy is not advised. Some problems can be red or yellow, depending on the specific neuromuscular disease involved and the severity of the complicating problem.

WEAKNESS OF VOLUNTARY MUSCLES (yellow)

Weakness of the voluntary muscles is an important part of almost all neuromuscular disorders, regardless of their precise cause.

In pregnancy, weakness of these muscles, especially those in the back, abdomen, pelvic girdle and hips, can lead to back pain, nerve compression injuries and loss of walking ability. Strength is not always regained.

During labor, the mother's weak muscles may prevent her from pushing the baby out during the expulsive, or second, stage of labor. A surgical delivery (Caesarean), or obstetrical instruments, such as forceps or mechanical suction, may be needed. Any of these adds to the risk of complications for both mother and child.

After delivery, the mother's weakness may, of course, impair her ability to care for the infant.

WEAKNESS OF INVOLUNTARY MUSCLES (yellow)

In some neuromuscular disorders, not only is there weakness of the voluntary muscles, but also of the involuntary, or smooth, muscles. The uterus is one of these, and weakness of uterine contractions poses some obvious problems for the pregnant woman. Labor may be prolonged, leading to maternal exhaustion and fetal distress; or, a prolonged labor may end in a Caesarean delivery, with its accompanying risks.

Of equal or greater importance, lack of uterine contractions after the delivery can lead to hemorrhage in the mother. After the baby is born and the placenta (spongy structure through which the fetus gets its nourishment) is delivered, the uterus has to clamp down on itself quickly to avoid prolonged bleeding from the uterine wall where the placenta was attached.

Weakness of involuntary muscles is common in myotonic muscular dystrophy.

PREGNANCY HORMONES AND AUTOIMMUNE DISORDERS (yellow)

During pregnancy, blood levels of the hormones estrogen and progesterone increase markedly. "We know for a fact that sex hormones influence the immune system through multiple mechanisms," says Dr. Yadollah Harati, a neurologist at Baylor College of Medicine and the Veterans Affairs Medical Center in Houston, where he has overseen the care of many pregnant women with neuromuscular disorders. "Estrogens in particular tend to bind to a special form of lymphocytes [immune-system cells] called CD8 cells." As estrogen levels increase in pregnancy, says Harati, there is a shift in the woman's immune system away from what's known as "cellular" immunity and toward what's known as "humoral" immunity, the kind that works through proteins called antibodies. The change may be part of the body's way of keeping a woman from rejecting her baby as she would a donated organ, but it can wreak havoc if she already has an immunologic abnormality.

In autoimmune disorders, such as myasthenia gravis, Lambert-Eaton myasthenic syndrome, polymyositis and dermatomyositis, the immune system seems to make a mistake; it turns against its own tissues -- muscle tissue or muscle blood vessels in myositis, and the neuromuscular junction (place where nerve meets muscle) in the myasthenias.

"If somebody has an underlying autoimmune disease, then the pregnancy will have an effect on the autoimmune disease," says Harati. "Sometimes in a positive manner, sometimes in a negative manner." In myasthenia gravis, it's hard to predict what pregnancy hormones will do. A third of pregnant patients with it get better; a third get worse; and another third stay the same. In myositis, Harati says, people tend to get worse during a pregnancy.

Autoimmune diseases often start in young women or during pregnancy, perhaps because of hormonal changes.

HEART PROBLEMS (red/yellow)

Women with cardiac disorders or congenital heart malformations have always had a hard time with pregnancy and delivery. Until very recently, many were advised not to attempt pregnancy at all.

The heart is a muscle, although a slightly different kind of muscle from both the voluntary and involuntary muscles. Unfortunately, it isn't spared in most muscular dystrophies, nor in many other neuromuscular disorders.

Pregnancy increases the demands on the heart considerably, especially in the later months. The normal heart can adapt, but the less effective heart often cannot.

When the heart can't pump enough blood around the body, tissues, including the placenta, which supplies the baby with nutrients, are deprived of oxygen. The oxygen-starved fetus may be damaged or even die. The woman with hypoxia may go into labor early and may give birth to a premature baby.

During labor, the heart has to work even harder than during the rest of the pregnancy; each uterine contraction increases its workload, making close monitoring and adjustment of medications and oxygen by skilled medical personnel essential to the safety of mother and child.

Heart problems are common in muscular dystrophies (especially myotonic dystrophy), Friedreich's ataxia and mitochondrial myopathies. They can also occur in nemaline myopathy, metabolic myopathies and polymyositis and dermatomyositis. They can occur in periodic paralysis during an attack of this disorder accompanied by abnormal potassium levels.

Ideally, the severity of the heart problem should be assessed fully prior to the pregnancy. Close cooperation among the pregnant woman and her obstetrician, neurologist and cardiologist must be part of the pregnancy and delivery.

DIABETES (yellow)

Diabetes isn't relevant in most neuromuscular disorders, but it's fairly common in myotonic muscular dystrophy and Friedreich's ataxia. The woman with diabetes and her baby are at increased risk for many complications.

Pregnancy tends to aggravate a diabetic or borderline diabetic condition, especially in the later months; in fact, many women develop diabetes (an inability to utilize sugars) only when pregnant. They have a disorder called "gestational diabetes." High blood pressure, anemia and infections are among the problems a pregnant woman with diabetes is more likely to experience than is the average pregnant woman.

If the mother's blood sugar remains high during pregnancy, her baby will absorb too much sugar and grow overly large. A large baby poses an obvious complication for labor and delivery, but the most serious problems are likely to occur after the birth. The baby's body has been making enough insulin to take care of the high blood sugar level it was exposed to in the womb; now, separated from the mother's circulation, it quickly has to adjust to life with a much lower blood sugar level. Unfortunately, it's not easy for the baby to adjust its insulin supplies quickly, and it may experience very low blood sugar in the meantime. Low blood calcium levels and respiratory distress may also occur, as well as any problems left over from a difficult delivery. The baby's heart and other organs may be enlarged because of the excess blood sugar.

The best way to prevent complications is for the mother's diabetes to be under optimum control during the pregnancy, with help from her obstetrician and perhaps internist or family practitioner.

EFFECTS OF MEDICATIONS FOR NEUROMUSCULAR DISORDERS (red & yellow)

Many medications taken by a pregnant woman can cross the placenta and enter the baby's circulation. Not all drugs are harmful to the baby, but many are, and others have simply not been tested.

Among the drugs used by women with neuromuscular disorders are those used to suppress the immune system and dampen the autoimmune reaction in such disorders as myasthenia gravis, Lambert-Eaton syndrome, polymyositis and dermatomyositis.

Corticosteroids -- drugs in the prednisone family (Deltasone, others) -- seem to be fairly safe during pregnancy, although their effects on the baby aren't fully understood. The so-called cytotoxic ("cell-poisoning") drugs, on the other hand, can cause severe birth defects or fetal death. These more potent immunosuppressants are sometimes necessary in autoimmune disease but are to be avoided during pregnancy if at all possible. Common examples are azathioprine (Imuran), cyclophosphamide (Cytoxan) and methotrexate (Folex, Mexate).

"You want to avoid drugs that have direct effects on the fetus, such as immunosuppressants like Cytoxan and azathioprine," Dr. Harati says. "But corticosteroids can be safely used and continued." If the woman is already on these potent immunosuppressants, he says, "we usually don't recommend pregnancy. We try to get them off those drugs and then allow them to wait for about six months to a year, and then they can get pregnant."

If the woman is already pregnant and on toxic drugs, the situation can be complex, Harati notes. "In any autoimmune disease associated with pregnancy, one has to weigh the risk and benefit of treating a patient and leaving the patient with autoimmune disease, which can itself affect the health of the mother and baby," he says. "You can [choose to] not treat the mother, in order to protect the baby, and then have a mother who's not healthy and is not able to deliver the child. So a balance needs to be struck between the risks and benefits to the mother and baby. It's a delicate balance and requires a thoughtful deliberation by all parties involved."

The best solution, he says, is for the woman's condition to be "under optimum, ideal control before she gets pregnant. That always is best."

EFFECTS OF MEDICATIONS USED DURING LABOR AND DELIVERY (yellow)

General anesthesia isn't as common in labor and delivery as it once was, but it still has its place, especially when emergency conditions require a Caesarean. (Local anesthesia, such as the popular "epidural," needs a longer time to take effect than general anesthesia.)

Anesthetic drugs are usually given at the same time as muscle relaxants. Medications in either of these categories can spell trouble for the woman with a neuromuscular disorder.

The most serious trouble is a condition called "malignant hyperthermia," a dangerous rise in body temperature with severe muscle spasms. (It has nothing to do with cancer.) People with various kinds of muscle abnormalities are more likely to have this untoward anesthesia reaction, which results from excess calcium being released from inside muscle fibers. Both inhalation anesthetics and muscle relaxants of the type known as depolarizing neuromuscular blocking agents can cause this condition. It can be rapidly reversed with a drug called dantrolene, but the anesthesiologist has to be prepared.

People with the myopathy known as central core disease are particularly prone to malignant hyperthermia. The condition can also occur with myotonias, periodic paralysis, metabolic myopathies and muscular dystrophies. These disorders seem to make people more susceptible to malignant hyperthermia than the average person, probably because their muscles don't react normally to the chemical changes brought about by the drugs.

Even without the threat of malignant hyperthermia, anesthetics and muscle relaxants can cause problems for the woman with a neuromuscular disorder. Women with myasthenias, for example, already have a defect in the way chemical signals go from nerve to muscle. Since neuromuscular blocking agents used with anesthetics further interfere with this process, normal doses of these drugs may work too well in myasthenia, causing dangerous paralysis of respiratory muscles.

Local anesthetics are generally considered safe in neuromuscular disorders, but even these have their risks. Epidural anesthesia is injected into a space just below the spinal cord, and that's the area where the anesthetic is supposed to stay. But sometimes the drug is absorbed into the bloodstream and reaches the heart, posing a significant danger to the woman who already has a cardiac problem.

If there's any significant spinal curvature, it may be impossible to use epidural or spinal anesthesia.

Sometimes, it's necessary to stop labor -- for example, if labor begins too early and threatens to result in the birth of a premature baby. A drug that's often used to stop labor (and also to treat seizures, a rare complication of pregnancy) is magnesium sulfate. Because it interferes with nerve-to-muscle signal transmission, it's not safe in women with myasthenia, who already have a defect in this system.

As with all potential complications, the key is knowledge and preparedness. The woman's obstetrician, neurologist and anesthesiologist have to understand the woman's condition and what they may encounter.

TRANSFER OF GENETIC DISORDER TO BABY (red & yellow)

Most women who carry genes for neuromuscular disorders, such as muscular dystrophy, are aware of the risk of passing on a disease or at least a carrier status to a child. Because each genetic neuromuscular disorder has its own inheritance pattern and all have reached different stages regarding genetic testing, it's best to consult a university-associated genetic counselor before beginning a pregnancy. But sometimes pregnancies happen when you least expect them; and sometimes, women and their partners decide to go ahead with a pregnancy despite the risks (as did many women we interviewed).

The most serious consequences of passing on a genetic disease are usually not known to the parents-to-be; those are the chances of a child developing the disorder while still in the womb. Such a situation is usually a disaster and can even be fatal to the child.

Myotonic dystrophy is a disorder in which this happens with a certain regularity. If the mother has the disease, she has about a 10 percent chance of passing it on to her child while the baby is still in the womb, a serious condition known as congenital myotonic dystrophy (CMMD). If she's already had a child with this condition, the chances rise to 40 percent for her next baby.

Congenital myotonic dystrophy involves joint contractures (fixed joints), mental retardation, weak muscles, feeding difficulties and respiratory distress. It's a much more severe condition than the later-onset form of the disease the baby's mother has. (A father with myotonic dystrophy can pass on the later-onset form but almost never the congenital form of the disorder. The reason for this is not known.)

Most genetic disorders that show up later in life don't seem to occur very often in the womb, but, if the disorder is among those that tend to get worse with each generation, this is certainly a possibility.

Of course, it's also important to consider the impact on both child and parents (especially if the mother is disabled) of a child being born with a later-onset disabling condition.

Good genetic counseling, consultation with the neurologist and some soul searching are advisable.

TRANSFER OF AUTOIMMUNE DISORDER TO BABY (yellow)

Genetic diseases aren't the only disorders that can be passed from mother to child during pregnancy. In autoimmune disorders, the mother makes antibodies (proteins produced by the cells of the immune system) against some of her own tissues; these can cross the placenta and sometimes attack the baby's tissues as well. The phenomenon has been best studied in myasthenia gravis, where about 15 percent of babies born to mothers with the disorder develop it themselves before birth and for several days to weeks after delivery. In some babies, the disorder is very serious, mostly because of the respiratory problems associated with it.

Good control of the mother's disease and careful monitoring during pregnancy are important. Reduced fetal movements during the pregnancy may suggest the fetus is affected by myasthenia. New tests to detect what's going on with the mother's antibodies and predict the baby's likely condition are in development. Meanwhile, a pediatrician or neonatologist should attend the delivery.

LACK OF SUPPORT AND PREPAREDNESS (yellow)

Dr. James Gilchrist, a neurologist at Rhode Island Hospital and Brown University School of Medicine, says he worries when he sees a patient who "can barely care for herself" who expects to care for a child without help. He says he recently saw a patient with muscular dystrophy and with "no spouse, no job. Now she's pregnant, and the baby will weigh more than she does by the time he's 4." Gilchrist, who has four children of his own, worries a lot about such patients because, he says, raising a child "is hard enough when you're physically well." It may not be politically correct, but he thinks a woman should consider whether she has a husband and whether the husband is completely committed to having the child.

LACK OF COMMUNICATION AMONG PROFESSIONALS (red)

The doctors we talked to emphasized above all else that lack of communication among the various professionals and between the pregnant woman and her doctors was a very serious risk. "Any pregnancy associated with neuromuscular disease has to be considered a high-risk pregnancy," Harati notes. "And these patients have to be seen frequently by an obstetrician who specializes in high-risk pregnancies. There has to be ample and close communication between the treating neurologist, the obstetrician and the patient. That is a must. In some conditions, such as myasthenia gravis or myotonic dystrophy, where we know that there is some effect on the fetus, there should be a neonatologist or pediatrician with a good knowledge of neonatal neuromuscular disease available. That person should be consulted from the beginning."

Harati says treating the pregnant woman with a neuromuscular disorder is sometimes a tough call. "One of the most difficult things in my practice is that, on the one hand, I'm very happy to see that my patient is going to have a child. I know that it is going to change her life in a very positive way forever; but on the other hand, I become very nervous and concerned about these women, about the baby, about the extra work it requires for everybody -- including myself!"

Gilchrist concurs. "Pregnancy is a worthwhile endeavor as long as it is discussed with the physician first," he says. "There is the potential for complications from conception to child. If it's not planned and discussed, it can be disastrous to both mother and fetus," he notes, telling a chilling story about a patient of his who lost two babies to neonatal myasthenia gravis. (Her third baby, under the care of Gilchrist and others, survived.)

At his institutions, he says, good communication is likely. "In the rest of the world, one hopes the obstetrician would get someone involved quickly. Obstetrician and neurologist have to get together. And as the woman approaches delivery, the pediatrician or neonatologist has to be involved."

Editor's Note: "What Worries Doctors Most" was prepared with the help of Dr. James Gilchrist, a professor in the Department of Clinical Neurosciences at Brown University School of Medicine in Providence, R.I.; and Dr. Yadollah Harati, a professor of neurology at Baylor College of Medicine in Houston. Gilchrist is an MDA clinic co-director at Rhode Island Hospital, and Harati sees patients at the MDA clinic at Baylor.