Dr. Greene’s Answer:

Corina, your situation is both dangerous and precarious.

Every snowflake is different and each person is even more so! Each cell in our bloodstream carries our own genetic signature. A constellation of proteins on the surfaces of the cells allows our bodies to distinguish between our own blood and someone else’s. These protein patterns are roughly divided into groups that we call blood types.

Not only are blood types different but some types of blood are incompatible with some others. The white blood cells in some types will perceive other types as enemies, attacking and destroying the other blood. This problem is most significant in people with Rh incompatibility.

People are called Rh-negative if they do not have the rhesus (Rh) protein on the surfaces of their blood cells. If Rh-positive blood cells get into the bloodstream of someone who is Rh-negative, the body of that Rh-negative person will see this as an enemy invasion.

Unprepared, the Rh-negative person will begin to make antibodies (what you call anticorps) against the foreign Rh protein. This first exposure is often not even noticed. The next time an exposure occurs, though, the body is primed to seek and destroy all Rh-positive blood cells. All-out war can occur inside an Rh-negative person’s body.

A terrible condition called hydrops fetalis can be the result of that war. Rh incompatibility produces a wide variety of outcomes. Sometimes only mild anemia and perhaps a little jaundice are the only signs there has been a conflict.

But sometimes the results are catastrophic. The first pregnancy is rarely a problem because blood is often not exchanged until the time of birth. But with each subsequent pregnancy, the risk for hydrops increases.

Hydropic babies are bloated, swollen, and pale. Enlarged hearts, livers and spleens are unable to perform their vital duties. The swollen lungs can make breathing impossible. Many hydropic babies are stillborn. Many die shortly after birth.

In 1963 an event occurred that began to change the story. Jorg Schneider, who was at the Freiburg University Hospital in Germany at the time, became the very first investigator to give pregnant, Rh-negative women a shot of Rh antibodies to prevent their immune systems from mounting their own response to Rh-positive cells.

The exact date of this achievement was August 9, 1963. One year later, Schneider reported that nine women, following delivery of Rh-positive children, did not develop Rh antibodies during subsequent pregnancies with Rh-positive fetuses.

Since then, prevention programs have been implemented in many countries around the world. In Great Britain, the number of deaths from hydrops has dropped 96% in the years since the prevention program began in 1970¹. This experience is typical.

By giving anti-D globulin (RhoGAM) to Rh-negative moms during and shortly after each pregnancy (including after miscarriages and abortions), 99% of mothers will not develop anti-Rh antibodies.² Unfortunately, about 1% still do.

Being Rh-negative is a recessive trait. This means that a person needs to have two negative genes to be Rh-negative and will always give one negative gene to any offspring. Being Rh-positive is a dominant trait. This means that an Rh-positive person can have two positive genes or one positive and one negative gene. If your husband has a positive and a negative gene, then about half of your offspring will be Rh-negative (and there should be no trouble carrying an Rh-negative child). But about half of your offspring will be Rh-positive (and if your mate has two positive genes, all of your offspring will be Rh-positive). This is a very risky proposition.

Healthy, Rh-positive children have been born to women with high titers, especially if they have had the RhoGAM and the titers are still high. Having a blood type B mom and a blood type A baby is also somewhat protective. But the pregnancy should be monitored closely and carefully managed by an expert in this area, even before conception. For a successful outcome, the baby may need blood transfusions every 3 to 5 weeks even before being born. Delivery is induced as early as is safe.

Even if birth is successful, the infant should be cared for at a well-prepared medical center. The baby may need aggressive treatment for anemia, immunodeficiency, and jaundice shortly after birth.³

When I was born, hydrops fetalis was an almost hopeless situation. Today, preventing Rh-negative moms from being sensitized is extremely (but not completely) successful at preventing hydrops wherever the guidelines are followed. All of this with a couple of simple, but ingenious shots! Once a mom has become sensitized things are not so simple. Future pregnancies may turn out fine, but sometimes massive, complex, medical interventions are necessary — and even with these, a good outcome may not be possible.

So, Corina, you have a very difficult decision to make. I’m afraid I cannot tell you whether you can safely have another child or not. But I do encourage you to weigh the odds, speak with your doctors, and to appreciate the beautiful, healthy child you already have.
Footnote References:
^{1 British Journal of Obstetrics and Gynaecology 1986 Sep;93(9):960-966
2 Williams Obstetrics, Appleton & Lange.1997
3 Pediatric Hematology Oncology 1998;15:193–197}

Dr. Greene’s Answer:

Having a baby is a lifelong responsibility and hopefully an even greater reward — for somebody! As a mother’s belly swells, she knows with deep certainty that the child is hers. Each time the baby moves or kicks, the bond between her and her child grows.

Depending on the situation, the father may be pretty sure that the child is his. For most of history, though, dads have had to rely on circumstantial evidence as the foundation on which to build this crucial relationship. After the baby was born, he could feel more sure he was the dad if the baby looked like him (“He has your feet, Honey!”), but often these early resemblances are at least partially creative imaginations.

In 1901 biologist Karl Landsteiner distinguished between three types of blood — groups A, B, and O. A fourth group — AB — was discovered a year later by another research team. As the inheritance patterns of these blood groups were worked out over the next decades, it became possible to use blood tests to exclude some men from being the fathers of some children. For instance, if the parents both have blood type O, then the children must all have blood type O. If a child were to have blood type A, B, or AB, then the presumed father must not be the real father. If the child’s blood type were O, then the presumed father might be the real father — but so might millions of other men. Here is a list of possible and impossible situations:

These are general rules, though, and exceptions apply. Very rarely, gene mutations may change the rules such that “impossible children” become possible. The geneticists at Stanford wrote a great explanation to this on the website for The Tech Museum of Innovation, at www.thetech.org/genetics/ask.php?id=181.

Today there are over 600 blood types known (as well as other tissue types called HLA types), which can make paternity testing far more accurate — but still not perfect.

It is also now possible to determine the father before a baby is born. This is done by comparing DNA molecules — our genetic blueprints. To do this you need a blood sample from both the mother and the potential father (testing without the mother’s blood is possible, but more difficult — and more expensive). You also need a small sample of amniotic fluid (the water that the baby is floating in). Less than 1/4 teaspoon is sufficient for the test. The amniotic fluid may be obtained by a process called amniocentesis. This procedure is performed no earlier than 13 weeks into the pregnancy.

A court order or informed consent of all adults involved is required to proceed with paternity testing.

You will need to wait 3 to 4 long weeks for the results. Waiting for these test results can be a very anxious time. Rush orders take 10 to 15 business days, but cost about $500 extra.

Either way, if the test says that a man is not the father, then legally and truly he is not (it can absolutely exclude some men as the father of a certain child). If the test says that he is the father, then he probably is — there is about a 99.8% chance that he is. DNA testing is now legally accepted as able to determine paternity.

There are about one million two hundred eighteen thousand five hundred males in Jamaica (as of 1992). A positive DNA paternity test could limit the potential fathers to only about 2,437 of them (plus 0.2% of the tourists). Only 2 out of 1000 men could possibly be the father. As you can see, a positive paternity test is good evidence, but not an ironclad guarantee.

Prenatal paternity testing can be arranged through a company called Genelex, located in Seattle, Washington. They are very helpful, and can be reached at 1.800.523.6487 or www.healthanddna.com/. The test costs $700.

If you wait until after the baby is born, DNA testing can be arranged through most local blood banks (many of which use Genelex). The blood sample can be obtained at birth. Otherwise, the baby should be at least 2 months old, since a fair amount of blood is needed for the test. In my area, this option costs about $600.

I realize that the circumstances that prompt a person to undergo paternity testing are often difficult. I hope that whatever you want turns out to be true. Even more, I hope that whatever turns out to be true becomes something that you learn to want.

Human blood genetics are quite complex because at each point there are a number of possible characteristics. Nevertheless, the genetics of human blood is far better understood than that of any other human tissue. To make things a little easier to understand, here are some guidelines for understanding how both the ABO blood types and the Rh system work.

The ABO Blood Types

• Each person receives an A, a B, or an O gene from each parent.
• The A and B genes are co-dominant, and the O gene is recessive.
• A person whose genetic type is either AA or AO will have blood type A, those with genetic type BB or BO will have blood type B, and only those with genetic type OO will have blood type O.
• A child with type O blood can have parents with type A, type B, or type O blood, but not type AB. Conversely, if two parents both have type O blood, all their children will have type O blood.

The Rh System

The Rh system is actually far more complex than the ABO system in that there are 35 different possibilities that one could inherit from each parent. These, however, are roughly grouped into positive and negative types. In this system the positive are dominant over the negative.

• If your genetic type is ++ or +-, your blood type will be Rh positive.
• Only if your genetic type is — will you be Rh negative.
• If both parents have Rh+ blood with the +- genes, they could have children who are ++, +-, or –. In other words, their children could be either Rh positive or Rh negative.
• Most children who are O negative have parents who are positive, since the +- combination is so much more common than the — combination.

Dr. Greene’s Answer:

Genetics can be so confusing! I can see how the issue may appear murky.

The modern science of genetics had its start in 1866 when an Austrian monk named Gregor Mendel provided a simple yet powerful description of how traits are passed on from one generation to another. Mendel’s work was unappreciated until 1900, more than fifteen years after his death. In his initial formulation, he described how sexual beings get two genes for each trait, one from each parent. The trait expressed, or visible, is a result of the interplay between these two genes. Specifically, he recognized that some genes are dominant and some are recessive. If you have one copy of a dominant gene you will express that trait, regardless of the other gene. In order to express a recessive trait you must have two recessive genes.

Mendel’s first experiments, though simple, were quite profound. He worked with peas, which had easily distinguishable traits, such as green versus yellow seeds. Each pea has two seed-color genes, one from each parent. The peas with two yellow genes were yellow. Those with a yellow and a green gene were also yellow; only those with two green genes turned out to be to green. Thus yellow was dominant over the recessive green gene.

The situation with human blood genetics is far more complex because at each point there are multiple possible characteristics. Nevertheless, the genetics of human blood is far better understood than that of any other human tissue.

First let’s look at the ABO blood types. Each person receives an A, a B, or an O gene from each parent. In this system, the A and B genes are co-dominant, and the O gene is recessive. Thus a person whose genetic type is either AA or AO will have blood type A, those with genetic type BB or BO will have blood type B, and only those with genetic type OO will have blood type O. This means that a child with type O blood could have parents with type A, type B, or type O blood (but not with type AB). Conversely, if two parents both have type O blood, all their children will have type O blood.

Another medically important blood type is described in the Rh system. These genes were first discovered in the rhesus monkey, hence the designation Rh. The Rh system is actually far more complex than the ABO system in that there are 35 different possibilities that one could inherit from each parent. These, however, are roughly grouped into positive and negative types. In this system the positive are dominant over the negative. Thus if your genetic type is ++ or +-, your blood type will be Rh positive. Only if your genetic type is — will you be Rh negative. This means that if both parents have Rh+ blood with the +- genes, they could have children who are ++, +-, or –. In other words, their children could be either Rh positive or Rh negative. Children who are Rh negative can have parents who are either Rh positive or Rh negative.

This is why two parents who have O positive blood could easily have a child who is O negative. In fact, most children who are O negative have parents who are positive, since the +- combination is so much more common than the — combination.

As it turns out, there are more than a dozen complete blood group systems other than the ABO system and the Rh system. This enables us to look at inheritance and family trees with greater precision.

Specific tests are available (through blood banks) to determine whether someone is a child’s parent.

Unless such testing indicates otherwise, there is no reason, based on your blood type, to be concerned that your parents might not really be your parents.